Good afternoon, dear guests of the Electrician's Notes website.
After publishing my articles about devices protective shutdown(UZO), I often began to receive the following question by email from website visitors: why do you need to install an RCD at all?
Let's figure out why you need to install an RCD in your apartments or houses?
It all depends on what goals you are pursuing.
The main purposes of using RCD:
- protecting people from electric shock
- prevention of fire due to electrical leakage current
Appearance of a single-phase (two-pole) RCD.
The use of RCDs to protect people from electric shock
When using electrical appliances such as a microwave oven, water heater, computer and others for personal purposes, there is a risk of electric shock, because the listed household appliances primarily have a metal body (conducts electric current) and complex internal circuitry.
Due to various influences (mechanical, thermal, etc.), as well as due to long term service, the insulation of the wires of these household appliances may become unusable.
By the way, this applies not only to electrical appliances, but also to electrical cable lines.
If the insulation of a conductor is broken, there is a possibility of a short circuit of this wire to the metal casing electrical appliance. In this case, a phase or, in other words, a potential equal to the mains voltage appears on the housing. But this will occur if the case is not grounded.
What happens if you touch the body of the device in such a situation?
To more clearly study and present the material on the use of RCDs, I will give you an example with a microwave oven.
Example 1. Without using an RCD in the circuit
If you simultaneously touch an electrical appliance, and in our example this is a microwave oven with damaged insulation, and any other object connected to ground, for example, a sink or battery, you will get an electric shock.
The consequences of such a “touch” can be very different. In one case it is a “mild fright”, in another there are serious consequences, up to cardiac arrest from the passage of current through the human body. Read, here are some real life examples:
Example 2. Application of an RCD in a circuit with a protective conductor
To prevent such consequences when the insulation of devices or cables is broken, it is necessary to use a residual current device (RCD).
But here such a situation will not happen at all, because... When a phase conductor is short-circuited to the metal body of an electrical device, a current will appear at which or the circuit breaker.
Again, I want to make a reservation, this will happen if you use electrical wiring with a protective conductor PE (phase, neutral, ground), i.e. system or .
Read about how to switch from the TN-C to TN-C-S grounding system.
Example 3. Application of an RCD in a circuit without a protective conductor
Let's consider the same example with a microwave oven using an RCD, but without the use of a PE protective conductor, i.e. With .
In this case, you have a chance to stay alive, because... the passage of current through the human body will be short-lived.
P.S. This is where I would like to end the article. The choice is yours!?
157 comments to the post “Why do you need an RCD?”
I am far from these questions)))
Everyone needs to know about the use of residual current devices. Thanks for the useful information.
If we are talking about electrical wiring in apartments, then many do not know what an RCD is. We don’t either, because the housing is old, even the traffic jams are old. And, if we talk about ASUs in buildings and residential buildings, then without an RCD it is generally impossible to submit the work. Of course, the answer is clear, you need to install an RCD, or better yet a differential automatic device.
As always, useful article on your site!
The information is very useful. Even I, a woman, know about this, although not in such detail. Now my knowledge has increased, thank you!
You have an excellent specialized site. Everything is written clearly and intelligibly
How many things have been invented on earth..) This is the first time I’ve heard about RCDs, but I’ve heard about grounding.. How to ground a washing machine?
How long ago was the RCD invented? And why didn’t they put it in before? residential buildings?
The use of RCDs is determined by the recently published new sections in the 7th edition of the PUE.
The device is undoubtedly useful, but who will install it?
Use the service of an electrical laboratory or electrician at your place of residence.
Georgy, I haven’t gotten around to writing the promised detailed article on this issue yet. But I explained the basic principles for using RCDs in a two-wire network in this article.
Everything was clear with the RCD, except for differences in connection. Thank you very much, great site!
You wrote “There is a controversial opinion that it is not permissible to use RCDs in old electrical wiring diagrams (two-wire). I will write my opinion on this matter in my own separate article.”
and “I take this opportunity to remind you that the use of RCDs in the TN-C grounding system is prohibited by the PUE.”
Where in Sverdlovsk region Is it possible to buy a socket with a built-in RCD?
I will also install an RCD at my place, the article will come in handy.
Andrey, regarding the ban on the use of RCDs in the TN-C system. In the PUE, clause 1.7.80 allows the use of RCDs, it says the following:
1.7.80. It is not allowed to use RCDs that respond to differential current in four-wire three-phase circuits(TN-C system). If it is necessary to use an RCD to protect individual electrical receivers receiving power from the TN-C system, the protective PE conductor of the electrical receiver must be connected to the PEN conductor of the circuit supplying the electrical receiver to the protective switching device.
You can read about the use of RCDs and much more in the book “UZO. Theory and practice." The author is an employee of the Moscow Energy Institute (MPEI). On page 227 of the book, the issue of using RCDs in the TN-C system is discussed.
In the article I tried to explain in detail that it is possible and even necessary to use RCDs without a protective conductor. This is an additional electrical safety measure when operating old electrical wiring with the TN-C system.
But here such a situation will not happen at all, because... when a phase conductor touches the metal body of an electrical device, a leakage current will appear, at which the RCD will trip and disconnect the damaged area.
THE QUESTION HERE IS NOT EVEN ABOUT THE UZO. LET'S IMAGINE THAT THERE ARE NO RCDs, ONLY AUTOMATIC MACHINES, WHAT THEN? IF THE PHASE APPEARS ON THE CASE AND THE CASE IS GROUNDED, BUT WE UNDERSTAND THAT SOMEWHERE THE PE CONDUCTOR MEETS THE N-CONDUCTOR, EITHER AT THE PLACE OF SEPARATION OF THE PEN CONDUCTOR IN THE TN-C-S SYSTEM, OR AT THE SUBSTATION ITSELF,.. THEN THERE WILL BE A SHORT BETWEEN PHASE AND ZERO, THE MACHINE WILL JUST CUT OUT!
Victor, if you have a two-wire network, then if there is a short circuit to the housing, there will not be a single-phase short circuit, but a leakage current will occur through the human body. The RCD will sense this leakage current and disconnect the damaged line.
Please tell me where it is better to install an RCD and which one for fire protection.
The input cable (25mm2 aluminum) from the overhead line is brought to the box on the facade of the house in which there is a VA 47 and a transfer from TN-C to TN-C-S is made, then a cable in a metal hose (6mm2 copper) along the facade of the house to the panel (in the house) with counter and automatic devices. By the way, I also want to install an RCD in the panel to protect against damage (after your articles). Single-phase power supply.
I would also like to control the cable on the facade.
Alexey, install a 300-500 (mA) fire protection RCD in the box immediately after the introductory VA47.
In the panel (in the house), install the input RCD at 100 (mA), provided that the RCD at 30 (mA) is installed on the socket groups. If they are not there, then it is better to set the introductory RCD in the panel to 30 (mA).
Do I place a 100mA RCD after the meter? What role does it play? But in the house, the groups are divided not by sockets and lighting, but by room, i.e. 1st VA for the kitchen, 2nd VA for the bathroom, + three more for each room, is this not against the rules? And how to install an RCD here? There are no small children - no one climbs into sockets with their hands. Maybe install a 30mA RCD in the kitchen and bathroom, and the rooms will be protected by a 100mA RCD??? Or is it better to install a diffautomatic machine in the kitchen?
Dmitry, which RCD will turn off faster: 63 (A) 300 (mA) type AC or 63 (A) 30 (mA) type S??? And is it possible to protect both of these RCDs with one 50(A) circuit breaker if they are connected in series?
Would you approve of this scheme?
In the box, immediately after VA47 50(A), we install a 63(A)300(mA) type AC RCD, then in the panel, after the meter:
1.VA47 32(A)+ RCD 40(A)30(mA) type A + consumers (including washing machine)
2. in parallel, another BA47 32 (A) + RCD 40 (A) 30 (mA) type AC + three BA47 10 (A) connected in parallel, from which the rooms are powered.
And here’s the question: can I put a 63(A) 30(mA) type S RCD right after the meter to protect these two 40(A) RCDs.. or is it better to put a 63(A) 100(mA) type AS RCD??? If the answer is yes, yes, can we protect sequentially installed RCDs (in the box and after the meter) with a BA47 50(A) machine, which is located in the box?
Have I confused you?
Introductory RCD at 100 (mA) - we decided on it. The RCD protects not only from small children (read the article), so it is advisable to install a 30 (mA) RCD for each group - this will be the ideal and correct option. If the budget is limited, then a 30 (mA) RCD is required for the bathroom (more on this) and for the kitchen also 30 (mA). There is a detailed article about the selectivity of RCD operation -. The rest is in the mail, send me a diagram (by hand if possible), I will check it and correct it.
please tell me, is it possible to just install one machine for the whole house?
+uzo (for all consumers at once), and not for each room with an automatic + uzo (total rated load on consumers up to 25A)
And I also want to make the following wiring diagram: electric meter-automatic + UZO-guard (against voltage surges)-consumers. Is this installation diagram correct? Question: how can I check the functionality of the machines and ouzo machines myself (they can also be defective)?
The functionality of the machines is checked by loading them with current. If you have an LATR, an ammeter, a current transformer and a little desire, then you can assemble this device yourself. I have a special stand for this - read more in the article about. The RCD is checked with the “Test” button.
In principle, you can leave one input RCD, then it needs to be set to 30 (mA), and if there is a leak in any circuit, the whole house will turn off.
I still don't understand how it works.
The resource is excellent, the presentation is clear and understandable.
Please help me in the following situation:
I want to install an outlet in the bathroom under washing machine.
I decided on the location of the socket (zone three), as well as the location of the cable. The house (socket) uses the TN-C system because I did not find different PE and N busbars in the floor panel, although in the kitchen there is a standard socket with “grounding”, in fact it was established that the outlet ground goes under a separate screw of the N bus of the floor panel, t .e. in fact, we have a zero. It is not possible to drag the soil into the shield separately. What do you recommend in this situation? I am inclined to use an RCD with the protective conductor of the socket connected to the N bus before the RCD. But what about the potential equalization system? Normally, the bathtub and pipes are connected to each other by a wire that is not connected anywhere else...
Dmitry, good afternoon!
I read the article you recommended, everything seems clear, but I still want to clarify your opinion once again - dividing the PEN conductor on the floor panel is incorrect, and the only option- this is to remake the ASU with the described division of PEN into N and PE with re-grounding of PE at the input and laying a separate PE line in the panel.
So do I understand?
(I’m just confused by the presence of a standard outlet in the kitchen, in which the “ground” goes through a separate screw zero bus on the board... And this has been the case since the building was commissioned in 1991)
Dmitry good afternoon! Give me some advice. I'm changing old electrical wiring in a 4-room apartment multi-storey building, equipped with electric stoves for a new copper wires. The house is powered using the TN-S system; there is no REN division until reconstruction.
I plan to install it in my apartment, according to design load and taking into account the demand coefficient, a 40A input circuit breaker, then an electric meter, then the entire load on separate lines:
1. For the electric furnace difavtomat AD-32 2R S16-30ma
2. For the electric heater in the bathroom difavtomat AD-12 S-16A-10ma
3. For the washing machine, differential automatic DM-60 S16-10ma
4 For quarter-common sockets on two lines AD-32 2R S16-30ma and 2 single-plug buses AAV S-16A
5. For lighting the apartment, a common difavtomat AD-32 2R S-16-30ma and 2 single-pipe automats AAV S-10A
Wiring wire VVGng copper cross-section 6.0 mm2; 4.0 mm2 and 2.5 mm2
What are the best automatic machines to use by manufacturer?
Dmitry good afternoon! In addition to the letter dated January 8, 2014. Please tell me that the grounding of the electric furnace must be dismantled when reconstructing the wiring, right?
A protective conductors from each email appliances, electric stove, washing machine, water heater for shower, sockets, etc. must be insulated in the electrical panel before
division of REN into PE and N and after that protected conductors from the electrical. connect the equipment to the PE grounding bus.
Good evening! I have a question: when I simultaneously touch the metal screw in the keyboard (connected via USB) and the battery, I start to receive an electric shock (unpleasant sensations at the point of contact with the battery), why does this happen, and is there a way to get rid of it?
Thank you, very useful site
Cool site! I learned a lot of new things, somehow I began to look at electricity in general differently), thank you very much for that! But still there is one question, I would be grateful: when changing the input cable (3x4) to the apartment (the house is 84 years old, most likely the TN-s system), the electrician took the phase from the packet in the floor panel, and connected the N and PE wires together under one the bolt on the body of the shield, as I understand it, I made a CHANGE (I could be wrong), please tell me if it’s worth leaving it like that? since I want to install an ouzo or differential in the apartment panel according to groups of cables (3x2.5)? It seems to me that ouzo and differential will not work like that when zeroed! thanks a lot in advance!
Evgeniy, you can’t do this during reconstruction, because... separation of N and PE must be carried out in the ASU at home. I wrote about this. The fact is that often there is no other way out and many electricians carry out the separation in floor panels, but this is still not correct. But RCDs and automatic circuit breakers work correctly with this connection.
Dmitry, thank you very much, that’s how I felt (although it’s not safe to feel in an electrician)), you need to know), then the last question, the most important for me: will I do the right thing in this situation by disconnecting the PE conductor in the floor panel (that is, will I remain without grounding) and hiding it there until better times of reconstruction in our house, but at the same time I will install protective equipment in the apartment panel (ouzo or differential, voltage control relay)?
That’s right, I wrote about this in the link provided in the previous post.
Dear Admin, how can I send you one diagram by email so that you can look at it and say whether it is NORM or not NORM)
My address email listed in the "Contacts" section. Send it and I’ll take a look.
IN country house During a thunderstorm, sockets spark, sometimes knocking out the general stabilizer for the house (Volter). How to protect?
PUE-7 prohibits the installation of RCDs in two-wire lines. The reason is that the RCD does not provide safety when exposed to voltage. A feature of any RCD is that it has a non-sensitivity zone, unlike circuit breakers, lies below the nominal setting. So for an RCD with a setting of 10 milliamps, from 0 to approximately 7.5 milliamps, the RCD is guaranteed not to trip, from 7.5 milliamps to 10 milliamps the RCD may or may not work, the response time is completely arbitrary. More than 10 milliamps - The RCD will work, but it is impossible to guarantee either the response time or the magnitude of the response current - it all depends on the type of RCD, operating conditions and service life, quality maintenance.No one wants to play with death. Therefore, a single clear standard for the performance of the RCD has been established - at three times the setting current (30 milliamps for a setting of 10 milliamps), the response time of the RCD is no more than 0.3 seconds. And this data is included in all calculations. The RCD will work earlier - the better.According to the international electrical safety standard for household electrical installations a current flow time of 0.3 seconds corresponds to a touch voltage of 70 volts and a current of 70 milliamps. If there is an RCD and 220 volts appear on the body of the electrical installation, then when you touch the “ground” a current of 220 milliamps appears, flowing for 0.3 seconds. And this does not meet safety requirements - a current of 220 milliamps, according to the standard, is allowed only for a time of 0.02-0.08 seconds. Therefore, the PUE prohibits the installation of an RCD in two-wire lines. But you can use an RCD, just not consider it a real protection. To do this, you need to determine possible ways leakage current and the resistance value of the leakage current path. So for a washing machine, water can serve as this leakage current path; no one does laundry without water. But you can’t protect a computer in this way. It’s better to cover the heating devices in the room where the computer is located with an insulated screen there will be no increased danger. And one more thing - a washing machine, a computer and many other things have a surge filter at the input, the middle point of which is connected to the case, so 110 volts are always “on duty” on their cases through the filter capacitors. If there is a path for leakage current , then the RCD without disconnecting the filter wire from the housing or the ground in the socket (third wire) will trigger falsely. Of course, with a sudden output of 220 volts to the body of the same washing machine and a leakage current path of 2-5 kilo-ohms through water within 0.3 seconds it will be 220 volts, which does not meet safety requirements, but you have to be especially lucky to be between the housing and the “ground” at this moment, and after 0.3 seconds the RCD will trip and prevent voltage from being on duty on the housing. So, if you are careful, its use is completely justified. And the third wire in the socket is not so good from the point of view of protection. If the protection is faulty in only one apartment and there is a short circuit to the 220 volt housing in all apartments and on all electrical installations connected to this wire generates a voltage of about 110 volts, while in an emergency apartment the wiring and the apartment itself burn until the higher protection works. In such systems you need highest level maintenance, which we don’t have. But we must remember - Soviet refrigerators with protection class 0 were used for decades in kitchens with increased danger and nothing. So you need to carefully check and measure everything in each specific case and the RCD will help.
VOLF 07/17/2014 at 12:20
Your comment is kind of long and scary, it’s difficult to highlight the main ideas, the descriptions of the situations are not completely clear, you have to figure it out yourself.
1. The RCD is considered an additional means of ensuring safety, the main one is grounding, but this cannot be the reason for the prohibition of the RCD.
2.According to the dead zone. For both circuit breakers and RCDs, the dead zone is always below the rated setting. As far as I remember, the RCD should be guaranteed to operate at a differential current of 2/3 of the rating, and not 3 of the rating.
3. Regarding the ban on the use of RCDs in the TN-C system. The PUE clause 1.7.80 says the following:
"1.7.80. It is not allowed to use RCDs that respond to differential current in four-wire three-phase circuits (TN-C system).”
I’ve read discussions on this issue before, I didn’t understand the reason for this ban (if possible, please explain to the Administrator), but I realized that this ban applies to the 3-phase part of the TN-C system, and in the 1-phase part of the TN-C system the RCD is quite can and should be installed.
4. On the topic “is the third wire in the socket good or not?” How can it be that if the protection is faulty (what kind of protection - from overload, from short circuit, differential?) in only one apartment and there is a short circuit to the 220 volt housing in all apartments and on all electrical installations connected to this wire (PE?PEN?) a voltage of about 110 volts arises, while in the emergency apartment the wiring and the apartment itself are on fire until the higher-level protection works? How can an accident in one apartment also affect the residents of other apartments? If you would like to continue the discussion, describe your situation more precisely, then we will continue.
5. There is no need to raise a hysteria, in such systems the highest level of maintenance is not required; for direct performers, 3 electrical safety groups and 3 qualification categories are sufficient.
Quote: “When insulation is broken electrical conductor, there is a possibility of this wire touching (contacting) the metal body of an electrical device. In this case, a voltage (phase) equal to the mains voltage appears on the housing. But this will occur if there is no chassis grounding.”
Only a phase will appear on the housing; there will be no voltage if you stand on an insulated floor (in apartments it is insulated) and do not grab grounded objects with your other hand, such as batteries, water supply pipes, etc. (the current will have nowhere to go).
Tolyan 09/17/2014 at 09:16
In fact, the voltage (phase) is measured not by the body, but by a voltmeter, one terminal of which is connected to ground, and it is this voltage that is discussed everywhere. But whether or not there will be an electric shock from it is a different question.
elalex, the concepts of “voltage” and “phase” should not be confused, because phase is a certain potential (one point), which in itself is not dangerous, and voltage is the potential difference between two points. If a person gets between these two points and a danger is created - the flow of electric current.
Alexey, that’s the whole point of my previous comment, that the phase on the body itself is not dangerous if there are no additional factors - water, pipes, etc. The point of that comment was not the lack of benefit of RCD in relation to electrical damage. electric shock, but the fact that many electricians still think that if they touch one bare wire, be it phase or neutral, they will be shocked (again, we exclude additional factors - water, conductive floors...). The author simply did not disclose this point.
Tolyan 02.10.2014 at 13:07
1. It is clear that for current to flow, it is not potential that is needed, but a potential difference.
2. The concept of “phase” can be defined in different ways. You can, for example, as in Wikipedia - “Phase in electrical engineering (colloquial) is a wire carrying voltage, that is, connected to the ungrounded contacts of a generator/transformer.” In general, the subject. But period?
3. There would be a phase on the body, and there will always be additional factors.
4. For those electricians who are very afraid of the phase, you can personally show the phase in your hands; I occasionally work like this. You can tell how electricians work on existing 750 kV power lines.
1. What I said.
2. They ride on carts.
Dmitry, hello.
You write that if you simultaneously touch an electrical appliance with faulty insulation internal wiring and floors with grounding will lead to electric shock to a person (without the use of an RCD in the circuit). I’ll ask a question, maybe a stupid one, but is the floor in our apartment also grounded? Please explain, thanks in advance.
Ivan 11/20/2014 at 11:04
The question is normal.
Only metal things can be grounded.
Electricians divide floors (and materials in general) into conductive and non-conductive. Stone, brick, concrete, wet walls and floors are considered conductive and connected to the ground, and the current through a person standing on such a floor is dangerous to life.
elalex thanks for the explanation, but tell me, standing on a wet floor and holding onto the body of electrical equipment on which there is a dangerous potential, the current flow path will be: body->person->floor->body?
Ivan 11/20/2014 at 16:48
1. In order for current to flow in a circuit, there must be a current source in it. There is no such source in the circuit you described, so the current will not flow along this path.
2. To better understand the problem, they usually draw the entire circuit, including the secondary winding of the transformer grounded at one end (usually 10 kV/0.4 kV), wires to the device with damaged insulation, and a person touching this device and standing on a naturally grounded conductive surface. Then the path of the damage current is better understood. The author, unfortunately, drew only part of this outline.
elalax November 21, 2014
Thank you very much for the competent explanation
I supplied the person with a two-pole ouzo from hager CD 264J, 30mA, 63A on an electric stove ( total power 8.5 kW i.e. approx. 38A) because they combined N and PE in the old socket of the stove and walled it up with expensive tiles - they refused to disassemble it - they did the repairs... They connected this PEN and L to the meter.
RCD Protects AB C40. Those. Input (PEN+L)-meter-AV-RCD-consumer.
I don’t see any point in splitting this PEN at the meter, but at the socket it’s a waste.
The RCD is triggered by the battery, the button works. I wanted to check for a leak - (please don’t hit me - I understand everything myself) with a finger through a moistened glove onto the radiator). By pressing the wire (L) from the output of the RCD (2) to the glove, I achieved a clearly noticeable breakdown through the finger, but the animal did not work. I tried it with salt water (output 2 and input N) - it worked, with tea - the same thing... Is this how it should be? It’s just amazing how crazy it has to be for it to work... Yes, I checked the phase through the same pipe - the bang was not weak, luminous at 6 mm.kv. even splashed. The AV and RCD switched off - they survived.
If you don't mind, please comment. (- read, as well as many other things on this and not only this site.)
Dmitry 12/10/2014 at 04:27
I had all this too. I installed it for a friend back in 1998. diff. 30mA, and my friend doubts that it will work when touching the phase. I had to manually convince that it would work. We went down into it damp basement, phase to the right little finger, little finger to the ground, hit - it didn’t work. I reassure you that the resistance of the little finger is high. I wet my little finger with water, hit again and again it didn’t work. My friend started accusing me. I had to reduce the resistance further - I poured a puddle of water on the floor, and it finally worked. Of course, I don’t do this for customers, but I set the supply resistance to 30mA (it should also work from 20mA).
Painters sometimes get into the phase under the protection of the diff, and it doesn’t work either, and they also blame me and my diff. I answer - it should not just hit, but grab it well.
In general, 30mA feels like quite a serious current to the touch, and you can’t measure it with your hands, only with the standard “Test” button, an external resistance of 10 kOhm or a lamp, but certainly not a short circuit to the battery,
Dear elalex and Dmitry, why are you subjecting yourself to such tests? From the point of view of electrical safety, this is extremely dangerous, and for a qualified electrician I consider this generally unacceptable. You don't test the operation of a circuit breaker by actually closing the circuit using a jumper, do you? Why does the customer have no doubts about the performance of the machines, but there are doubts about the RCD? And if such a model of behavior is transferred to 10 (kV) electrical installations, then I’m actually afraid to even imagine...
To check the RCD there is a “Test” button, and there are also special devices. As a last resort, the RCD can be checked with an additional resistance (), calculated for the required leakage current. But I think that pouring water under your feet and showing the functionality of the RCD is unnecessary.
Answer:Admin
12/10/2014 at 15:11
Well, if you apply a similar practice to testing 10 kV lines, then it will roughly look like this in the video: vk.com/video-52632047_165514430?hash=f5365d266a78e41a
I remember you wrote that links cannot be inserted into comments, but before you decide what to do with these comments, watch the video. Real example what will happen. Yes, and the question is, is there an RCD for a line of 10 kV and above? I have never met for high voltage networks similar protection devices.
The video is terrible!
There are no RCDs in 10 (kV) networks. There are protections whose operating principle is somewhat similar to the operating principle of an RCD, but they have their own names.
Networks with a voltage of 10 (kV) are always performed with an insulated neutral. Ground fault currents in such networks are relatively small, but nevertheless, to monitor ground faults, an insulation monitoring relay, or IZ for short, is installed in the additional winding of voltage transformers. In the event of a 10 (kV) phase short circuit to ground, the relay is triggered and sends a signal to the control panel. To troubleshoot a ground fault in a 10 (kV) network, according to our in-plant instructions, no more than 2 hours are given. I plan to write a detailed article about this, because questions on this topic are often asked.
The outgoing feeders have earth protection, which is triggered when a ground fault occurs in the cable lines and turns off the feeder. For more responsible consumers, ground protection is performed not for shutdown, but for signal. To the shell power cable install a zero-sequence current transformer (ZCT), among themselves they call it ferrantium, and students without hesitation call it “donut”. A photograph of the TTNP and a connection diagram for the earth protection relay is shown in.
There is also differential protection of lines and transformers. But in a nutshell I cannot explain the principle of their operation.
Thank you for your promptness. Installed everything. Testing RCD with tea produces an effect! I will take your comments into account. Apparently, you will have to get yourself a 10 kOhm (.022 A) resistor.
Please help me figure it out! I have this question, but first a little outline of the situation - There is a power switchboard with a rated current of 79A; in the head of the switchboard, for fire-fighting purposes, it is necessary to install differential protection. leakage current, usually in these cases I used IM, but IM is produced by brands known to me, up to 63A, in this case I decided to use VD and in the IEC catalog I found a table according to which it is necessary to set the VD with a rated current one step higher than the protective one automatic, we choose a 100A automatic, there is a 125A VD, Schneider, Siemens, Abb, but these are very expensive devices for budgetary institution. The question is the following: what, in your opinion, is the reason for the need to install a high pressure motor coming after the machine, one step higher? rated current automatic? (I am considering the possibility of installing both a machine and a high-voltage generator of the same rated current)
Oleg 12/19/2014 at 23:45
1. Your question about the relationship between the ratings of the machine and the difrel has already been answered several times on this site: the machine allows long-term (up to an hour) overload, up to 1.45nm, for which the difrel should be designed.
2. If you also accepted the idea of a fire protection circuit breaker and did not look closely at my comments, I will ask you a question: why is this fire protection device needed? If you have the same arguments as others, I can argue with you in the same way.
Oleg 12/19/2014 at 23:45
By the way, if you want to analyze other aspects of the situation with the electricity supply of your budget institution, describe it in more detail. There are clearly still ways to cut costs.
Hello.
Will the ouzo turn off if a short circuit occurs? It is clear that it is intended for other purposes, but still?
Sergey, the RCD will not work during a short circuit, but there are exceptions.
Sergey 12/23/2014 at 15:56
It is almost impossible to wind the primary winding of a differential transformer with phase and neutral wires in exactly the same way; there will always be some difference in the number of turns, even if only a fraction of one turn. But at high short-circuit currents, this fraction of one turn provides a magnetizing force sufficient to trigger the RCD, which is what happens in practice.
Good afternoon. I heard that there are sockets and adapters with a built-in RCD. Question: is it possible to use them in a two-wire network?
And another question: is there a replacement planned? gas stove with oven on gas panel And electric oven. How to properly connect an electric oven in a two-wire network?
Denis, any RCD, whether built-in or external, can be used in two-wire TN-C networks. They will work correctly, with only a slight difference. For example, in a three-wire network (TN-C-S), if a phase fails on the body, the RCD will immediately trip, and in a two-wire network (TN-C) - only when touching the human body - the article shows visual illustrations of such situations.
Read about connecting electric stoves
Good afternoon I wanted to know if a 100mA RCD will help save you from a fire? How less value, the less thermal power, just a wooden house)
Ilshat, RCDs with this cut-off rating are exactly what they call fire protection
Ilshatu 03/09/2015 at 11:39
1.100mA is 220x0.1=22W of allocated power. Take a 25W incandescent lamp and make a couple simple experiments- pour dry tyres on it, turn it on, see the result. Do the same with sheets of paper. Tell us.
2. Maybe you know, I personally am against a 100mA RCD if there is a 30mA RCD next to it.
Ilshat, if the house is wooden, then first of all you need to comply with the requirements for laying electrical wiring in it (here), and then choose the ratings of protection devices and RCDs.
elalex, and what is the connection with, why don’t you install a 30 mA RCD after the 100mA RCD? After the 30mA RCD, they put it on a 10mA RCD.
Thanks everyone for the answers
Ilshatu 03/10/2015 at 01:51
You misunderstood me. I always place a 30mA RCD, and a 100mA RCD in front of it - only if there is a significant distance between them. But there is no point in installing 100mA and 30mA RCDs in the same cabinet. There was a discussion about this somewhere before.
TO VOLF:
07/17/2014 at 12:20
GOST R 51326.1-99. Automatic switches controlled by differential current for household and similar purposes without built-in overcurrent protection
5.3.4 The standard value of the rated non-breaking differential current IΔn0 is 0.5IΔn.
5.3.12 Standard values for the shutdown time (see 3.3.9) and non-shutdown time (see 3.3.10) for AC RCCBs are given in Table 1.
maximum shutdown time of RCCB general type with differential current:
IΔn - 0.3 s
2IΔn - 0.15 s
3IΔn - 0.04 s
maximum tripping time of type S RCCB with differential current:
IΔn - 0.5 s
2IΔn - 0.2 s
3IΔn - 0.15 s
minimum non-tripping time of type S RCCB at differential current:
IΔn - 0.13 s
2IΔn - 0.006 s
3IΔn - 0.05 s
(It seems to me that there is a typo in the table. For the non-tripping time of type S RCCBs at a differential current of 2IΔn, one zero after the decimal point is superfluous).
Mikhalych 03/27/2015 at 22:55
Maybe VOLF is no longer alive, and there is no one to argue with?
Hello. Tell me to connect neutral wire or not on the housing of electrical receivers in the TN-C system (for example, a stove, washing machine, lamps). I think it’s impossible, because if the neutral wire breaks (in the switchboard, or in some other place before the power receiver), the housing will be energized. Correct me if I'm wrong.
I understand what the RCD is needed. I would like to make sure that without an RCD in the TNC system it is impossible to set a zero on the housing
Dmitry, you are right - NIZZZZZZZZZYY!!!
Dmitry:
04/25/2015 at 07:22
In the TN system, the letter N denotes the connection of metal cases and other conductive parts with the neutral of the supply transformer using a neutral conductor. According to the PUE of the seventh edition, when the cross-section of the copper neutral working conductor is less than 10 sq. mm for protective zeroing A separate neutral protective conductor with a cross-section of at least the phase conductor must be used. In a TN system, the use of an RCD is not necessary, because when a phase is short-circuited to the housing, short-circuit protection is triggered.
If the housing of the electrical receiver is not connected to the neutral wire, you will get a TI system not provided for by the PUE. In this case, the use of an RCD for protection against indirect touch Necessarily.
Mikhalych 04/26/2015 at 15:12
1. In the TN system, the use of an RCD is not necessary; let those who touch the exposed wire die?
2.What is the TI system? Maybe TT or IT?
elalex:
04/26/2015 at 22:39
1. There should be no possibility of touching the bare wire. All live parts must be insulated, fenced or placed out of reach. To protect against electric shock in the event of insulation failure in the TN system, it is used automatic shutdown nutrition. To do this, all exposed conductive parts are connected to the neutral of the power source. A short to frame becomes a short circuit. The circuit breaker trips and cuts off the power. If the instantaneous release setting is correctly matched with the phase-zero loop resistance, the use of a protection device that responds to differential current is not necessary.
2. There is no such option in the PUE, but in residential buildings old building often exists.
The first letter is the state of the neutral of the power source relative to ground:
T - grounded neutral;
I - isolated neutral
The second letter is the state of open conductive parts relative to the ground:
T - open conductive parts are grounded, regardless of the relation to the ground of the neutral of the power source or any point of the supply network;
N - open conductive parts are connected to the solidly grounded neutral of the power source.
When the apartment is wired with a two-wire cable, the sockets do not have a contact for connecting the protective conductor, the TN system ends in switchboard at the entrance. Open conductive parts of electrical receivers in the apartment are isolated from the ground. If the insulation is damaged, phase voltage will appear on the housing relative to ground. If you simultaneously touch the body and metal structures connected to the ground, a current of about 200 mA will flow through the human body, which is not sufficient to trip the circuit breaker. The use of an RCD with a differential breaking current of 30 mA in this case will give a chance of salvation.
By the way, according to clause 1.7.51. The PUE as the only protection against electric shock due to indirect contact allows “insulating (non-conducting) rooms, zones, areas.” That is, automatic power off to protect against indirect contact can not be used if the room has plastic pipes, non-conductive floors and walls, metal radiators heating units have non-conductive barriers or are placed out of reach.
Mikhalych 05/05/2015 at 22:58
1. There is no need to quote and explain the PUE too much, I am an electrical engineer, a former chief power engineer and am quite familiar with them.
2. Naturally, there should be no possibility of touching a bare wire, etc. But for some reason it happens. Is it necessary to save people in these cases with the help of an RCD? PUE and you think it’s not necessary. I think it is necessary. What do you think, which of us is a man and which is a beast?
Mikhalych:
04/26/2015 at 15:12
If you carefully read the PUE ch. 1.7, 7.1, then the installation of an RCD is mandatory in most cases.
There should not be most cases, there should always be an RCD.
And yet it is not clear about fire-fighting RCDs for 300-500 mA. Why such a high leakage current?
I didn’t know that 10 kV overhead lines are always made with an insulated neutral. As I understand it, all sorts of pumping units on a floating barge in a river and floating houses on the water, also with an insulated neutral, an isolation transformer?
These are different - overhead lines on the ground and electricity. food on boats. On the ground, it’s easy to look up, count the wires and figure out the circuit, but on the substation everything should be isolated from the housing, both three-phase three- and four-wire networks, incl. and DC networks, if according to the rules, and ultrasonic insulation monitoring devices, however, as in mines, have been around for a long time and have been around for a long time.
And large RCD currents so that there are no false alarms from everything, only from something serious. However, an RCD with 300 mA can be easily triggered in the event of a breakdown of the gas arrester and varistor due to overvoltage from the same lightning.
Valery 07/22/2015 at 12:27
1. Firefighters believe that the minimum emitted power sufficient for a fire is 60 W, this is a current of 60/220 = approximately 300 mA. All RCDs with a current up to 300 mA inclusive are fire protection. Such large leaks (300mA) can only be the sum of the leaks of a branched network, but not any single cable. There are standards for cable insulation. I don’t know how it is now, but before it was at least 500 kOhm, what kind of leaks there are!
2. An isolation transformer is a theoretical invention of the PUE developers. Of course, if desired, it can be made, but has anyone ever seen it in real life? Why is it needed at all if there is an RCD?
3. An isolated supply neutral is available in the army, mines, and among consumers - in 3-phase 380/220V motors (I once argued that it would be better if the motors had a neutral connected).
for surfactants 07/22/2015 at 13:40
To eliminate false alarms from lightning, there are lightning-resistant RCDs.
If there is, then it will be difficult to change it, because... You won’t be able to change it yourself - everything is pre-registered - the RCD and the machine are sealed together with the RES meter and I don’t see the point in paying a lot of money for calling, unsealing, replacing, new seals. So far, my arresters have been vigilant and working on their work - there have been no false ones, but there have been real overvoltages along power lines-10.
Is it possible to install a 30 mA ouzo immediately after the input circuit breaker so that it controls the entire wiring of the apartment/house as a whole, or will it always trigger falsely due to natural leaks?
Leo
1. Some kind of failure occurred - I received a letter, but your message is not here.
2. You can install a 30 mA RCD immediately after the input circuit breaker, but it depends on where, what and how you have it:
— Personally, I am categorically against introductory machines in apartments. I can explain if you want;
- in private houses, an introductory machine is needed, but it is better to install an RCD after the meter;
- depending on what natural leaks you have. If they are large enough, you need to divide them into 2-3 30mA RCDs.
Hello, I need help. The school, in a fit of parental zeal, is asking for help in installing electrical wiring. computer class. They say there is no money for the project, the essence is 20 workstations plus 2 scanners, 2 printers, 2 MFPs and a poektor, power the piglets' sockets through an RCD or RCBO. From operating experience, I know that RCDs conflict with office equipment when large quantities this one. The question is how many workstations can be placed on one device and what type is optimal to choose. You will have to shake money from your parents, and sometimes this is hopeless; in our class three people never fail, although I can only classify one family as low-income. I wouldn’t want to miss the calculations, otherwise, in addition to work, I would have to buy equipment at my own expense.
Paul:
08/19/2015 at 18:07
The computer lab must have grounding or separate wire potential equalization nickname and connected to the nearest switchboard or ASU. Because on the body system unit there is potential, it is related to work pulse block nutrition. With grounding to one RCD, you can connect an infinite number of workstations, naturally, according to calculations.
Nikolay
08/19/2015 at 18.07
If I understand correctly, installation of a potential equalization bus is required, regardless of the fact that the wiring diagram is three-wire
For: Pavel 08/19/2015 at 18:07
As far as I understand, you need to stretch the legs over the clothes. How can it be that there is money for computers, but not for classroom equipment? As far as I understand, a desktop computer is more expensive than a netbook? Why do you need 2 scanners, 2 printers, 2 MFPs for training? Who controls the money? What is there, corruption? An electrician should not be interested in this, but for parents to cover up the theft of money is not the case.
For
Lion:
08/09/2015 at 01:39
Paul:
08/19/2015 at 18:07
The protection zone of the RCD is limited by leakage currents. There is a capacitance between the cable conductors. Almost no current flows through the capacitance of the N-PE circuit, because the voltage between them is negligible. And a phase voltage is applied to the L-PE circuit and the capacitive current L-PE leads to inequality of currents L and N in the RCD measuring circuit. At the input of electrical receivers having pulsed sources power supply, install noise suppression filters with capacitors between L-PE and N-PE. Here the leakage current of the L-PE circuit will be significantly greater.
According to PUE clause 7.1.83. “The total leakage current of the network, taking into account the connected stationary and portable electrical receivers in normal operation, should not exceed 1/3 of the rated current of the RCD. In the absence of data, the leakage current of electrical receivers should be taken at the rate of 0.4 mA per 1 A of load current, and the network leakage current at the rate of 10 μA per 1 m of phase conductor length.”
For an apartment, most likely, one RCD will be enough. But for a computer lab with 20 workstations it may not be enough. You need to measure the leakage current.
If there is current clamp, allowing you to measure a current of 10 mA with sufficient accuracy, then pass conductors L and N through the magnetic circuit of the clamps. Pass the PE conductor past the clamps. Connect workstations according to a temporary scheme. When the unbalance current reaches 10 mA, the protection zone of one RCD is complete.
If there are no clamps, then by connecting calibrated resistors of the appropriate resistance and power, you can create a leak between L and PE at the output of the RCD. The load from the RCD output must be turned off. When the current is less than 15 mA, the RCD should not operate. By decreasing the resistance, increase the leakage current until the RCD trips, but not more than 30 mA. If the RCD response current is less than 15 mA or more than 30 mA, the RCD is faulty. Increase the resistance so that the leakage current is 10 mA less than the actual tripping current of the RCD. Connect the loads before the RCD trips.
Mikhalych 08/31/2015 at 23:14
1.Which complex procedure RCD checks!
2. I cannot believe that within a class there would be a leakage approaching 15-30mA through the cable insulation. And that the RCD protection zone cannot cover the entire class.
3. The inequality of currents L and N in the measuring circuit of the RCD under class conditions will not have any effect on the RCD.
4. Let’s not forget that the current in a class network is pulsating, an RCD requires type A. Plus, there is a theoretical problem with the third harmonic in the neutral wire of a 3-phase network.
5. Instructions from the PUE on the estimated current leakage from the phase wire - a filkina letter.
6. Do you think there are current clamp meters that can measure a current of 10 mA with sufficient accuracy? I think their scale starts at no less than 0.5A.
What is the best RCD to buy for a house with old wiring; in one room there is no grounding in the sockets. There is an automatic stopper installed near the meter.
Valentin 09/20/2015 at 05:49
1. I hope you are not poor, do you have an automatic washing machine, TV, computer, maybe light dimmers? Then the electromechanical RCD of type A is suitable for the cross-section of the wires (one step larger than the automatic one). These are rare items on sale. The cheapest ones are from Hager, say CD263J. And it’s better not just one, but 2-3 (there should be more machines than one).
2.Is there grounding in the other room? Or do you have a grammatical error?
3. Due to old wiring, the RCD may knock out, and may not even allow switching on. I get nervous in such cases.
4.Ruthlessly throw out the automatic plug and place a normal automatic machine under the cross-section of the wires.
Good afternoon
Probably, some of my questions have already been answered in different posts, but since I am not an electrician myself, I ask, if possible, to give an answer to my specific situation.
The object is a wooden bath house made of timber. The wiring will be all open, partly retro, partly cable duct, sleeves, etc. Three-wire circuit. Ground loop. Power supply comes from an old house where there is a panel with a meter (there is no ground there and the circuit is two-wire).
The question is about the shield of the new house, or more precisely, about its contents.
After reading many articles on this site, I drew for myself the following wiring diagram at home. We install DA-300mA 32A in the panel of an old house. From it we pull a protected (corrugated sleeve) wire VVG-Ng (approx. 10m) to the terrace of the new house, then approx. 8m -on the terrace before entering the house itself to the panel.
In the panel at the entrance there is a regular 32A circuit breaker (general shutdown), then there are groups of lights (2G), sockets (4G), a water heater - for each corresponding YES 10 and 16A.
The electricians who will perform the installation convince me that this is not entirely true. Their option: in the old house - a simple 32A automatic machine (no land - no need YES), in the new home-at the entrance(general off) - regular circuit breaker 25A, light - two groups of regular circuit breakers 6A each, socket groups - YES 16A each.
It’s difficult for me to argue with them - they are professionals (that’s for sure). But I would really like the house to have the maximum possible fire safety (most importantly!) and other safety measures via email. current
I will accept with great gratitude your well-reasoned (for me and for them) comments and recommendations. Your answer is very important to me! And if this is possible, your specific option for my situation.
Andrey 09.24.2015 at 07:40
I answer in the same order of presentation as yours.
1. The grounding circuit in a new house is using the TT grounding system (1 pin is enough, there is an article by the Administrator), pass it along the third wire of the incoming power line to old house, where, if possible, spread throughout the house.
2. Nowhere in the houses are there any automatic machines or simple machines with protective characteristic C, only electromagnetic RCDs 30mA without protection against overloads and short circuits, and automatic circuit breakers har.V.
3. Decide on the loads in the new house.
4.Measure the resistance of the phase-zero loop in an old house in any way - either with special electrical laboratory devices (tedious, time-consuming, expensive), or using the kettle and voltmeter method yourself (cheap and cheerful). Only then select the machine and the cable cross-section for new home. If you protect the cable with corrugation outdoors, it will not last long.
5. In the panel of a new house there is no input circuit breaker, 1-2 RCD 30mA + line circuit breakers. In terms of differential protection, the power supply circuit will be non-selective - when the RCD in the panel of the new house is triggered, the RCD on the line in the old house will also be triggered.
6.The type of RCD 30mA (A or AC) and the ratings of the circuit breakers of the socket lines depend on what will be turned on in the sockets of the new house.
7. The fact that electricians are professionals is not an argument - they can do things wrong all their lives. Every time you doubt that they are right, demand an explanation of the logic and motives for making their decisions. If rules are mentioned, let them show those rules. If they can’t explain, justify and show, shoot them in the neck. You can try submitting the content of your disputes here to the site. But their reasoning “no land - no need for defensive protection” is alarming - defensive protection is needed always and everywhere, regardless of the availability of land. Bad electricians are afraid of differential protection - it immediately shows all their mistakes.
8. Don’t forget that in the bath high temperatures and heat-resistant light and cables (wires) are required. There seems to be an article on the site about the bathhouse.
Thanks for the detailed answer. If possible, clarification. Is it necessary to drag earth into an old house (it will just be a utility block)? If we consider the option without land in an old house: what needs to be changed in the power supply scheme? In an old house, do we leave the machine for entry into a new house or set it to YES (without land!?)? In the panel of a new house (already a three-wire circuit) there is a 30mA input RCD? I really don’t understand why not 100 or 300mA?
Then there are several groups of lighting (one RCD 16A 30mA), sockets (for each - YES 30mA), a separate water heater (YES 30mA)? What's wrong here?
Thanks in advance for your answer. I'm looking forward to it. You need to decide today!
Andrey 09/25/2015 at 09:01
1. Even though the old house will be a utility block, will there still be sockets and lamps that require grounding? Maybe at some point you will distribute it to consumers there? If not now, then let one core of the power cable of the new house wait for this moment. I think the third core is not a problem for you?
And in general, if the power supply to your site occurs through an old house, then the grounding needs to be plugged there.
2. I already wrote:
“3. Decide on the loads in the new house.
4.Measure the resistance of the phase-zero loop in an old house in any way - either with special electrical laboratory devices (tedious, time-consuming, expensive), or using the kettle and voltmeter method yourself (cheap and cheerful).”
The difavtomat rigidly binds 3 in one device different types protection, and that's bad. Such a device that you personally need may not exist in nature.
In an old house, on the line of a new house there should be a simple circuit breaker + RCD (without short-circuit and overload protection). Which ones will be determined after completing the old points 3 and 4, and now the new point 7.
Stop mentioning the land next to the RCD. The earth is on its own, the RCD is on its own, they are not connected in any way.
5.In the panel of a new house there are 2-3 30mA RCDs, which simultaneously protect both people and the house from fire. Any 100-300mA RCDs are simply superfluous, although they are mentioned by all and sundry, and in different places schemes.
If you have extra money, you can increase the number of introductory RCDs to three, I don’t see any point anymore.
6. Based on the meaning of the previous message, I understood that in the new house there will only be a bathhouse, and nothing else. If you live there, then this is a completely different and big conversation. This is called the power supply scheme for an individual residential building.
After the introductory RCD there should be 2-3 lighting lines and a bunch of lines of sockets, as long as you can stand it. Personally, I make 2 lines of sockets in each room, and even more in the kitchen. Everyone has their own simple machine gun. I repeat, there are no automatic machines anywhere, stop mentioning them.
All the resulting lines are distributed in some reasonable way between the input RCDs.
7.Until the old points 3 and 4 are completed, there is no point in talking further.
Obviously, measure the resistance of the phase-zero loop (before the street transformer substation) in an old house you will have to use the kettle and voltmeter method yourself.
I think so, the voltage input to your area comes from overhead line. Determine the material and cross-section of the outlet from the overhead line to the old house. Tell us what the counter looks like and what's around it.
8.If your new home and home appliances there will be quite a lot of roads in it, you will have to think about a voltage relay and internal lightning protection.
Andrey 09/25/2015 at 09:01
The first thought is not always the best. According to a sensible second thought, installing a 30mA output RCD in the old house and the same RCD in the new house at the same time does not make much sense.
It makes special sense to transfer the power supply line of a new house from the air to the ground, to plastic pipe. Then in an old house there should be an RCD not 30mA, but 100mA, and even better it would be selective or lightning protection. And there will be selectivity between the RCD in the old house and the RCD in the new house.
I live in a two-family house (two identical halves with their own entrances).
The neighbors have input via SIP, our half is connected in parallel (cable in a pipe in the attic). Double wiring, reinforced concrete house. There is a basement with an earthen floor.
I want to add to three 16 A circuit breakers (one is a basement, the second two rooms and a bathroom, the third a kitchen, a room and a hallway) on the panel after the meter three 30 mA RCDs and ground at least the washing machine by placing another one in front of it RCD 10 mA.
1. Are your thoughts sound?
2. Is it possible to make grounding in your basement by drilling a hole for the wire in the floor next to the washing machine and driving a steel angle 63 into the earthen floor in the basement to a depth of 1.5 meters?
3 Will my activity in any way affect my neighbors’ electricity?
PS. The floor in the house (except for the bathroom) is made of plywood and covered with linoleum. Is it non-conductive?
And one more question.
I have my laptop on the windowsill; when I sit at it, my knees touch the heating radiator (it’s warm and pleasant in winter). The laptop is powered by a standard separate power supply, it seems to be 12 V.
Is it safe?
Dmitry 09/26/2015 at 01:26
1. The floor made of plywood and linoleum is non-conductive, although depending on what kind of linoleum it is, it can also be conductive to remove static charges, but it has the same conductivity as plastic.
2. Sound thoughts, depending on how to add three 30mA RCDs, this can be done in different ways.
3. The washing machine on your floor is the same machine as the others; there is no particular point in distinguishing it from others.
4. It is necessary that people do not walk on the ground around the grounding in the basement, or pave the entire ground around the grounding with a non-conductive coating.
5. Should not be reflected.
elalex, thank you. I will try to implement your recommendations as much as possible. I'll write about the result. By the way, I'm going on vacation, email. installation is due and this is delayed for two weeks - I don’t want what they would do without me.
Dmitry 09/27/2015 at 02:10
There is 19-20V and double insulation, it is safe until lightning strikes and breaks through the insulation.
1. It turns out that when using a PE conductor at a facility, the current will never flow through a person, but will go through the PE conductor, thereby causing the RCD to turn off?
Why in this case is it still important to select the RCD leakage current (10 and 30 mA)? Judging by the description, it is worth thinking about choosing the leakage current of the RCD if there is no PE conductor. The only case that comes to mind (in the case of a PE conductor) is that a phase breakdown to the body household appliance occurs at the moment when a person holds on to the body.
2. What is the reason for choosing a 10 mA RCD for wet rooms?
1. This is important to eliminate cases of false triggering of the RCD
2. Wet areas are classified as high-risk
Alexey, thanks for the clarification. The question is closed.
The question is whether to switch to TN-C-S system in a separate apartment apartment building with old wiring TN-C is not entirely relevant and correct. The question is not whether someone who is thinking about it should switch. He thinks, but his neighbor has long since moved on without thinking. The question is what to do in apartment building, some of whose apartments have already unauthorizedly switched to TN-C-S, the danger of which is obvious.
The second part of the question - what is interesting is not so much the question of switching a single apartment to TN-C-S, this is definitely impossible, the PUE is categorical. The question is whether to install protection based on differential current. The answer is to install, preferably, a modern automatic machine instead of a conventional machine, with separate overcurrent and leakage levers, but after that the apartment cannot be considered protected. At the same time, this will provide some protection both in case of damage to the insulation and “from fools” in the mentioned apartment building. This is exactly what the old letter from Energonadzor indirectly speaks about.
But the lack of a automatic rifle is a manifestation of arrogance. IMHO.
Sergey 11/15/2015 at 16:02
1.You have piled up God knows what. The impression is that you don’t understand what you’re talking about.
2. It seems that you do not understand the difference between TN-C and TN-C-S.
3.How is it separate apartment maybe switch to TN-C-S? What does the PUE say about this transition?
4. Why do you like difavtomats so much? Are they somehow better than RCD+automatic?
5.What are these separate overcurrent and leakage levers? Have you ever seen a difavtomat?
6. What other protection is there both in case of insulation damage and “against fools”?
7.What is another old letter from Energonadzor?
8. Why is the lack of a automatic rifle a manifestation of arrogance?
Good afternoon, Dmitry. I appeal to you and everyone knowledgeable people with a request to clarify some points regarding the connection of an RCD in an old house with a TN-C grounding system.
Dmitry, in the comments to another article you wrote “it is prohibited to install RCDs in the TN-C system according to the PUE (clause 1.7.80). But it is also stated below that “if it is necessary to use an RCD to protect individual electrical receivers receiving power from the TN-C system, the protective PE conductor of the electrical receiver must be connected to the PEN conductor of the circuit supplying the electrical receiver to the protective switching device.”
How to understand this phrase? Third conductor from plug socket I have to connect to the PEN conductor, but where? To the floor panel body? or directly to the wire itself? Yes, but what about your advice in the article about dividing the PEN conductor into PE and N:
“What to do when the wiring in the apartment is done according to modern PUE requirements, and the supply line is still two-wire?
I answer: in this case everything is very simple. In the apartment panel, you connect all the PE protective conductors to your PE bus, but you don’t connect the PE bus itself anywhere and leave it “in the air” until your house is transferred to the TN-C-S system.”
Those. The PUE says that you need to connect to the PEN conductor, but it immediately says that you don’t need to connect. Confused...
Hello! What’s not clear is this! If a phase appears on the body, and at this time we touch any device that is connected to ground, sink or batteries, we will receive a discharge. The question is, why are the sink and the battery grounded? Where?
Let's separate the flies from the cages - grounded devices are one thing, and seemingly grounded ones are another.
The water pipe may well be grounded; no one insulates it in the ground. Everything that is somehow connected with this pipe can also be grounded, although often defective - threads, rust...
Heating pipes and radiators are not grounded, they are even insulated and contact with the ground can be through a device to which the cold room is connected. water mixer, For example.
The sink, if metal, is exactly the same, ceramics, etc. in no way, except through water resistance, which is different for different sources. How much - and x/s!
You can also get hit thanks to the capacitive component of the body, even when standing on a rubber mat.
To answer your question accurately, you need to know many things in detail. I just can’t say that it will work or it won’t.
You can also be hit by your system unit, even standing/sitting on the floor and not touching anything else with your second hand, if its body is not grounded through a plug to normal ground. Not fatal, but sometimes noticeably unpleasant. But there is a different reason - the network filter, which MUST BE GROUNDED. Sometimes the refrigerator pinches - leakage, often.
Therefore, everything that has a grounding contact must be grounded.
THANK YOU!
Do I understand correctly why you can’t reset household appliances?
Let's say we grounded the washing machine, suddenly a phase breakdown occurred on the body, and since the body is grounded, will a short circuit occur? if it happens, then the machine will work, right? And if in addition we have an RCD, then it will also work, maybe even faster if it touches the housing or drum at that time! So what's the danger?
And secondly, if we have a full-fledged separate grounding made in accordance with all the rules, when a phase breaks down on the body, the current should flow through the grounded conductor, but somewhere there was a break in this conductor, does that mean life is again at risk? Or, for example, in the event of a breakdown with full grounding, a person touched the drum, then the current will flow through less resistance of the person than through a grounded wire!
Ruslan, if you are afraid of this: ... the current should go through a grounded conductor, but somewhere there was a break in this conductor, then that means life is at risk again? ... (c), then any conductor - phase or neutral - can burn out or break in exactly the same way ...
Install an RCD, what's stopping you?
And who told you that the resistance of the human body is lower than that of a grounded wire?
Thanks for the answers! Yes, you are right, that’s what I’m hinting at, why grounding is prohibited, although the same problem can happen with grounding! And yet, my apartment has two wires, I really want an electric oven, so in connection with this there are a lot of questions! If you don’t do grounding, there’s no question of grounding, then at least an RCD will help in an unfavorable situation?
And you do it as you did in houses with electric stoves during the USSR - to the point where both the neutral and the ground converge in the distribution board, and there was such a thing, drag a separate wire, non-disconnectable!, it will be grounding, no matter what, if there are no others . There is an opportunity - 1st, 2nd floors, to make a separate grounding - do it.
Unfortunately, there is no way to stretch the cable since repairs have been made, and floor 4, what remains is an RCD or DIFAVTOMAT
Ruslan, and it’s good that it’s not. The fact is that when dividing the PEN conductor (common zero) into floor panel with the outdated TN-C grounding system, in essence you are grounding the housings of your devices, and in the event of a break in the main neutral from the ASU to the floor switchboard (more about this), the potential difference (voltage) will be at all neutrals metal parts Your devices. If you touch the body of the device, you will be exposed to electric current. It’s good if an RCD or automatic circuit breaker is installed in the line. Therefore, either don’t nullify anything, or do it instead of in the floor panel.
Good afternoon.
I decided to learn to understand electrics at least at the everyday level and came across your site. The site is wonderful. Study and study.
Please tell me.
In our apartment a few years ago private master The electrical wiring was changed, grounded sockets and a separate apartment panel were installed.
The working zero and phase go from the floor panel to the RCD, and the grounding goes to a separate block. The electric stove and sockets are connected via an RCD. The groups of sockets and the stove after the RCD are separated by automatic machines. The working zero after the RCD comes to another separate block.
For lighting, the diagram is as follows: zero working and phase lights are taken from the input contacts!!! RCD (already suspicious), then the phase light goes to its own separate machine, and the zero worker went directly from the RCD. All this is in the apartment panel.
There is only one common machine left on the floor panel.
The grounding wire in the floor panel is connected to a block; the standard grounding sign is stamped on this block.
The house was built in 1982, the system is most likely TN-C.
Now I’m worried, how did it connect to the floor panel? Maybe the PEN conductor was separated and my electrical appliances were neutralized? And can it star at any moment?
— When there is a break in the zero to the floor panel, the voltage on the housings generally appears on all electrical appliances or only when there is a phase short circuit to the housing?
- With such a connection scheme in the apartment as I described, if there is a break in the zero from the ASU to the floor panel, will some kind of protection work, an RCD or an automatic device?
— Doesn’t the devices spontaneously combust in this case?
— How can you determine visually which system is used in the floor panel? The diagram on the door is unreadable.
— Can I send you a photo of the shield?
Please help me, I’ve read so many of your articles that I’m on a powder keg)))!!!
The question is: can Dagenergo come and say install an RCD so that we can seal the meter?
Denis, with TN-C-S or TN-S systems, you should have three wires going from the floor panel into the apartment.
One is phase.
The second is working 0 (N), moving away from the block, which should be installed on the insulators.
The third is a protective 0 (PE), extending from the block with this marking. This header must be installed directly on the mounting panel.
If two wires or three wires go into the apartment, but two of which are connected to blocks installed directly on the mounting panel, then this is a TN-C system.
Victor, thank you very much for your response, the floor panel is a complete mess, and there are also a bunch of cut old wires)))
I also dug into the site, trying to figure out the home wiring. Denis, look at the article about errors in connecting RCDs, where connecting the zero after the RCD to the bus is considered incorrect. I haven’t yet understood why.
Alexander
After the INTRODUCTORY RCD, you can and should connect the zero to the bus (100 ml or 300 ml). It is fireproof and not so sensitive... Unlike (30 ml, 10 ml) which will be triggered when the neutral wire of the neutral wire is connected to the common bus...
For sockets RCD-30 ml, (10 ml)..
Just automatic machines are born….for the input of the RCD 300 (100) ml, after the introductory automatic machine.
I tested the ouzo in the tn-c system the hard way: my ouzo protects one branch and with the back of my hand I leaned against the battery pipe and quickly ran the phase over my hand. The interesting thing is that sometimes it grabbed weakly and the cord worked, and sometimes it grabbed harder and didn’t work.
WHY was it so different??? please answer!
otherwise I split into two. because some say it cannot be installed in this system, while others say it can be installed. although experiences on myself incline me in favor of betting
Dmitry,
Author and employee of the Moscow Energy Institute
who wrote the book “UZO. Theory and practice." states, quoting the Book:
Electrical installation of an RCD in an old two-wire system, which is still found in most old houses, is USELESS. Moreover, such a system does not meet the requirements of the PUE. Therefore, first of all, your home should be equipped with a system grounding TN-S or TN-C-S, that is, three or five-wire cable line..
The human body is a conductor of electric current. The resistance of dry, intact human skin can be up to 80,000 ohms, resistance internal organs is 800 - 1000 Ohms, so the calculated human resistance to electric current is taken to be 1000 Ohms or 1 kOhm.
It is not difficult to calculate that the value of this current can be 0.22 A, or 220 mA, and death is possible when exposed to a current of 100 mA. Thus, first a person will be shocked by an electric shock, and only then, perhaps, the protective shutdown device will de-energize the group line.
You should also know that by installing a residual current device (RCD) in the power switchboard, you are thereby modernizing (reconstructing) the power supply system. The rules for electrical installations clearly state such actions.
Why is there such a discrepancy in the opinions of 2 competent specialists???
Nikolay, the author of the book writes correctly, including about the modernization of the grounding system. By the way, I have a separate and very detailed article on reconstruction and modernization on the website -. But if it is not possible to upgrade, then the RCD will still provide protection against leaks in the electrical wiring in the event of an electric shock. It definitely won’t be superfluous. Now compare the two situations.
1. Let's take the same example from the book. Let this be a leakage current of 220 (mA). Let's say you have a 30 (mA) RCD installed in your apartment. Let's assume that on a microwave oven a phase has penetrated into the housing. You went and touched its metal body, i.e. came under the influence of electric current. The RCD will react and operate within a time of about 0.005-0.01 seconds. If you don’t believe me, here’s an article where I use a special device at different currents. Fast?! I would say even very quickly! There is a very high chance that an electric shock will pass without serious consequences, because The fundamental factor is certainly not only the magnitude of the current, but also the time of its exposure to the body.
2. The same example, only without an RCD. Do you understand the difference?! That in this case there is nothing to turn off and the machine will not work in this case, which will put the person under voltage into great danger.
Thanks for the answer Dima.
In any case, the RCD gives Big chance to preserve health and life!!!
Then why does the author of the book write correctly??? Why doesn’t the PUE require the installation of this protection in the TN-C network, because the advantages are obvious??????
Because in the TN-C network the RCD breaks the PEN wire in this way, which is unacceptable, and in the new GOST the installation of an RCD in the TN-C system is prohibited. But, as they say, it is better to save your life than to unquestioningly follow the rules. IN own apartment you need to switch to the TN-C-S system as soon as possible, but centrally, as part of the overhaul program.
Vladimir, why is breaking the PEN conductor unacceptable?
Alexey, PUE 1.7.145
It is not allowed to connect switching devices in circuits of PE and PEN conductors, except when powering electrical receivers using plug connectors.
Vladimir, if it’s not difficult, please explain the instructions:
It is not allowed to connect switching devices in circuits of PE and PEN conductors, with the exception of cases of power supply to electrical receivers using plug connectors
Nikolay, what is there to explain? It is prohibited to break the combined PEN conductor and PE protective conductors with switching devices (automatic machines, switches, etc.). This is primarily due to their necessary continuity for electrical safety purposes.
Dima, that is, when installing an RCD in the TN-S and TN-C-S networks, we break only the phase and neutral wires (N), and when installing in the TN-C network, we break the phase and PEN conductors, right?
But after the RCD, this conductor only functions neutral conductor…. I'm not getting something (
The PEN conductor carries the function of a PEN conductor up to the division into PE and N. Such division can only be done on the input buses switchgear, re-grounding PE.
Dear Admin!
Please explain what type of electrical network is available in the apartment building, if staircase(three apartments per floor, 9 storey house) on inside One of the doors of the panel with meters and machines has an explanatory sticker with the following content (house according to the so-called “Lithuanian project”):
To the previous post:
Is this TN-C or TN-C-S?
Or something “in between”?
I'm especially confused by the last "A" in the "ABCNA" designation in the diagram.
what kind of wire is this?
In the entire apartment, all sockets except one have two wires (phase and neutral).
Only one socket has three wires (the only socket with grounding “horns”, located in the kitchen).
The house was built approximately 1994-1995.
Sergey, the most common TN-C system is three phases and zero. And another phase A is a separate line for powering floor outlets, nothing more. We have exactly the same schemes, and there is even a separate article about one of them - .
Thank you for your answer, dear Admin!
If you don't mind, a few more questions.
Is it possible to use it in such a house, in an apartment with two-wire sockets, to protect against electricity when connecting and using a washing machine, for example? next device: “Adapter with protective shutdown UZO-DPA16V 30mA IEK”?
Will this device work properly when connected to a two-wire socket, given that both the plug and socket of this Adapter initially have contacts for the third wire (i.e., the ground wire)?
Or is it necessary to connect the washing machine through a two-pole RCD?
The aluminum two-wire wiring in the apartment is already about 22-23 years old, does it make sense to replace it with a new copper (three-wire) one?
How do you feel about the idea? possible installation Is there an RCD near every significant socket or should I use it everywhere where I need an adapter similar to the one mentioned above with an RCD?
Thank you in advance for your attention!
Here is this “Adapter with protective shutdown UZO-DPA16V 30mA IEK”:
Currently, for some reason, this model has been discontinued, but leftover inventory is still sold everywhere.
Do you have any information why it is no longer produced?
Exactly the same in 16 floors from the 1980s... The socket in the kitchen is three-pin for electricity. slabs
It’s up to you to decide on replacing the electrical wiring, especially since it’s difficult to give an adequate assessment remotely. In any case, it has served quite a bit, and besides, it does not correspond modern requirements. If you are planning a renovation in the near future, then definitely think about replacing it.
Good afternoon
What's the point of installing an RCD? After all, if a phase falls on the body of the device, there will be a short circuit and the machine will be knocked out. Unless from a fire.
Albert:
08/17/2017 at 14:38
Good afternoon
What's the point of installing an RCD? After all, if a phase falls on the body of the device, there will be a short circuit and the machine will be knocked out. Unless from a fire... (c)
Albert, first of all, explain the meaning of the words “the phase will fall on the body”! Where, when, under what circumstances, in what apparatus, then we will try to understand the meaning of the need for an RCD. At the same time, write about the presence of grounding for this apparatus.
How the RCD works:
All RCDs belong to the category of electronic protective equipment. However, in my own way functional purpose, the residual current device differs significantly from standard circuit breakers. What is their difference, and how does an RCD work in comparison with an automatic machine?
Everyone knows that over time, wire insulation ages. Damage may occur, and the contacts connecting live parts gradually weaken. These factors ultimately lead to current leakage, which causes sparking and further fire. Often, such emergency phase wires energized devices may be accidentally touched by people. In this situation, electric shock poses a serious danger.
Purpose of RCD
Residual current devices must respond to even minor short-term current leaks. This is their main difference from circuit breakers that operate only during overloads and short circuits. Automatic machines have a very high time-current response characteristic, while an RCD operates almost instantly, in the presence of even the most minimal leakage current.
The main purpose of the RCD is to protect people from possible electric shocks, as well as to prevent dangerous current leaks.
Operating principles of RCD
From a technical point of view, any RCD is a high-speed switch. The operating principles of the residual current device are based on the response of the current sensor to the changing current flowing in the conductors. It is through these conductors that current is supplied to the electrical installation, which is protected by the RCD. A differential transformer is wound onto the core, which is a current sensor.
To determine the response threshold of an RCD having a certain current value, a highly sensitive magnetoelectric relay is used. The reliability of relay structures is considered quite high. In addition to relays, they have now begun to appear electronic designs devices. Here the threshold element is determined by a special electronic circuit.
However, conventional relay devices seem to be more reliable. The actuation of the actuator is carried out using a relay, as a result, a rupture occurs electrical circuit. This mechanism consists of two main elements: a contact group designed for maximum current and a spring drive that breaks the chain in the event of an emergency.
To check the serviceability of the device, there is a special circuit inside it that artificially creates a current leak. This triggers the device and makes it possible to periodically check its serviceability without calling specialists to carry out electrical measurements.
The direct operation of the RCD is carried out according to the following scheme. A situation should be considered where the power supply system is operating normally and there are no leakage currents. The operating current passes through the transformer and induces magnetic fluxes directed towards each other and equal in magnitude. When they interact, the current in the secondary winding of the transformer has a zero value, and the threshold element does not operate. When a current leak occurs, an imbalance of currents in the primary winding occurs. Because of this, a current appears in the secondary winding. Thanks to this current, the threshold element is triggered, and actuator is activated and de-energizes the controlled circuit.
From a technical point of view, the residual current device consists of a fire-resistant plastic housing. On its back there are special locks for installation on electrical panel. In addition to the elements already discussed, an arc suppression chamber is installed inside the housing, which neutralizes the electric discharge arc. Clamps are used to connect the wires.
RCD operation parameters
For the right choice device response settings, be aware of the danger AC for a person. Under its influence, cardiac fibrillation occurs when contractions are equal to the frequency of the current, that is, 50 times per second. This condition causes a current starting from 100 milliamps.
Therefore, the settings at which the RCD is triggered are selected with a margin of 10 and 30 milliamps. The lowest values are used in high-risk areas, such as bathrooms. The highest settings are 300 mA. RCDs with such settings are used in buildings, protecting them from fires due to damaged circuits.
When choosing an RCD, the rated current, required sensitivity and number of poles are taken into account, in accordance with the phases of the supply network. It is necessary to check the degree of thermal stability of the device, as well as the ability to turn it on and off, based on the calculated network parameters.
The rated current value for the RCD must be higher than that of the machine. A lower current rating of the machine will protect the RCD from damage in the event of a short circuit in the circuit.
How to connect an RCD
All terminals on the RCD body are marked with the corresponding letters. Terminal N is for the neutral wire, and L is for the phase wire. Therefore, they must be connected to their own terminals.
Also, it is necessary to take into account the position of the entrance and exit and under no circumstances change their places. The entrance is located at the top of the device. The power wires running through the input machine are connected to it. The output is located at the bottom of the RCD and the load is connected to it. If you confuse the position of the input and output, then false triggering of the residual current device or its complete failure to operate is possible.
Installation of RCDs is carried out together with conventional circuit breakers. Thus, devices installed together provide protection not only from short circuits and overloads, but also from leakage currents. At the same time, the RCD itself, which is connected behind the input machine, is protected.
Connecting a residual current device in an apartment or private house has its own characteristics. For apartments where it is used single-phase network, the RCD connection diagram is assembled as follows, following a certain sequence: input machine => electricity meter => the RCD itself with a leakage current of 30 mA => all electrical network. For consumers with high power it is recommended to use your own cable lines with connection of separate residual current devices.
In large private houses, connection diagram protective devices differs from apartments due to its specifics. Here, all devices are connected as follows: input circuit breaker => electricity meter => input RCD with selective action (100-300 mA) => circuit breakers for individual consumers => RCD for 10-30 mA for individual groups of consumers.
RCD errors when connecting
Correct connection of protective devices is key reliable operation the entire electrical network.
Basics purpose of RCD is the protection of people from electric shock in the event of a malfunction of electrical equipment (being energized as a result of insulation damage) as a result of accidental or unconscious human contact with live parts. Also preventing fires caused by ignition of electrical wiring due to the flow of leakage currents.
Operating principle of RCD
Operating principle of RCD? - Many people ask this question.
As you know from an electrical engineering course, electric current flows from the network along the phase wire through the load and returns back to the network through the neutral wire. This pattern formed the basis for the operation of the RCD.
If these currents are equal, I in = I out, the RCD does not respond. If I in > I out the RCD senses a leak and trips.
That is, the currents flowing through the phase and neutral wires must be equal (this applies to a single-phase two-wire network, for a three-phase four-wire network the current in the neutral equal to the sum currents that flow in phases). If the currents are not equal, then there is a leak, to which the RCD reacts.
Let us consider the principle of operation of the RCD in more detail.
The main element of the design residual current devices is a differential current transformer. This is a toroidal core on which windings are wound.
At normal operation network, the electric current flowing in the phase and neutral wires creates alternating magnetic fluxes in these windings, which are equal in magnitude but opposite in direction. The resulting magnetic flux in the toroidal core will be equal to:
Ф ∑ = Ф L - Ф N = 0
As can be seen from the formula, the magnetic flux in the toroidal core of the RCD will be equal to zero, therefore, the EMF will not be induced in the control winding, and the current in it, accordingly, will not be induced either. In this case, the residual current device does not work and is in sleep mode.
Now let’s imagine that a person touched an electrical appliance that, as a result of damage to the insulation, found itself under phase voltage. Now, in addition to the load current, an additional current will flow through the RCD - leakage current.
In this case, the currents in the phase and neutral wires will not be equal. The resulting magnetic flux will also not be zero:
Under the influence of the resulting magnetic flux, an EMF is excited in the control winding, and under the influence of the EMF, a current arises in it. The current generated in the control winding activates a magnetoelectric relay that disconnects the power contacts.
The maximum current in the control winding will appear when there is no current in one of the power windings. That is, this is a situation when a person touches a phase wire, for example in a socket, in this case no current will flow in the neutral wire.
Despite the fact that the leakage current is very small, RCDs are equipped with magnetoelectric relays with high sensitivity, the threshold element of which is capable of responding to a leakage current of 10 mA.
Leakage current This is one of the main parameters by which an RCD is selected. There is a scale of nominal differential currents shutdowns 10 mA, 30 mA, 100 mA, 300 mA, 500 mA.
It should be understood that the residual current device reacts only to leakage currents and does not work during overloads and short circuits. The RCD will not work even if a person simultaneously touches the phase and neutral wires. This happens because human body in this case, it can be thought of as a load through which an electric current passes.