Phase and neutral wire. What is zero and phase: how to determine phase and zero yourself. The resistance in the circuit is measured

When installing sockets and light switches, connecting household electrical appliances, it becomes necessary to determine the purpose of the wiring cores. How to determine phase and “zero”, as well as the grounding conductor? This task, which is not difficult for professional electricians, sometimes baffles those who are little familiar with the rules of electrical networks. Let's try to understand this issue.

Construction of household electrical networks

Household electrical networks at the entrance to the distribution panel have a linear voltage of 380V three-phase alternating current. Wiring in apartments, with rare exceptions, has a voltage of 220V, since it is connected to one of the phases and the neutral conductor. In addition, properly installed household wiring must be grounded. In older buildings there may not be a grounding conductor. Thus, when installing wiring and electrical appliances, it is necessary to know the purpose of each of the two or three wires.

You should also know the rules for connecting various devices. When installing a conventional socket, the phase and neutral conductors are connected to the terminals in any order, and the grounding wire, if available, is connected to a copper or brass bus. The switch is connected to a phase wire so that when it is turned off, there is no voltage in the lamp socket - this will ensure safety when changing lamps. Complex household appliances in a metal case must be connected in accordance with the markings of the wires, otherwise the safety of their use is not guaranteed.

Devices and tools

Before you begin electrical installation work and determine the phase and zero in the wiring, you need to prepare the necessary instruments and tools:

• Pointer or digital multimeter;
• Indicator screwdriver or tester;
• Marker;
• Pliers;
• Knife for stripping insulation.

You also need to find out where the protective equipment is located: circuit breakers or plugs, RCDs. Usually they are installed in a distribution panel on the site or at the entrance to the apartment. All operations on connecting electrical equipment and stripping wires must be carried out with the circuit breakers turned off!

Rules for working with a tester and multimeter

Checking the phase using an indicator screwdriver is carried out as follows: the screwdriver is clamped between the thumb and middle finger of the hand, without touching the uninsulated part of the tip. The index finger is placed on the metal patch at the end of the handle. The sting touches the bare ends of the wires; when it touches the phase conductor, the LED lights up.

A multimeter measures the voltage between the conductors. To do this, the device is set to the alternating current measurement limit with the symbol “~V” or “ACV” and a value greater than 250 V (usually for digital devices the limit of 600, 750 or 1000 V is selected). The probes simultaneously touch two conductors and determine the voltage between them. In household electrical networks it should be 220V±10%.

Sometimes, to determine the grounding conductor, it is necessary to measure resistance. To do this, set the measurement limit “Ω” on the multimeter or with a bell icon.

Attention! In resistance measurement mode, touching the phase wire and ground loop will cause a short circuit! This may result in electrical injuries and burns!

Visual method of determination

If the wiring is done according to all the rules, you can determine the phase, neutral and grounding conductor by the color of the insulation. The ground wire is a two-tone yellow-green color, the neutral wire insulation is blue or cyan, and the phase wire can be white, black or brown. You can verify the correct connection using a visual inspection; in this case, it is necessary to check the color matching of the insulation not only in the panel, but also in the distribution boxes.

Visual inspection sequence

1. Open the panel and inspect the circuit breakers. Depending on the design load, their number may vary. Only phase or phase and neutral wires can be connected through the machines. The grounding conductor is always connected directly to the bus. Check that all wires are color coded correctly.
2. If the color of the insulation of the cable going into the apartment in the panel corresponds to the rules, open all distribution boxes and inspect the twists. In them, the colors of the neutral and ground wire insulation should also not be mixed up.
3. Switches are connected to the phase in distribution boxes. Installation is often performed with a two-core wire having other insulation colors, for example, white and white-blue. This shouldn't bother you.
4. If the installation is carried out in full compliance with the color of the insulation, it is enough to check the phase wire using an indicator screwdriver.

Determining phase and zero in a two-wire network

If your wiring is done without a grounding conductor, you only need to find the phase conductor. The easiest way to do this is with an indicator screwdriver.

An indicator screwdriver will help determine phase and zero

1. Turn off the circuit breaker and strip the insulation of the wires at a distance of 1-1.5 cm using a knife. Place them at a distance that prevents accidental contact of the wires.
2. Turn on the circuit breaker. Using an indicator screwdriver, touch the stripped ends of the wires one at a time. A glowing diode will indicate the phase wire.
3. Mark it with a marker or colored tape, turn off the circuit breaker and make the necessary connections.
4. When connecting lighting fixtures, you must also make sure that the switch is connected to the phase wire, otherwise, when changing light bulbs, it will not be enough to turn off the switch; you will have to completely de-energize the apartment each time by turning off the machine.

Determination of phase, zero and ground wire

If the network is three-wire, but is made with wires of the same color, or you are not sure of the correct connection, you must determine the purpose of the conductors before installing each element of the network.

1. Determine the phase wire using the method described above using an indicator screwdriver and mark it with a marker.
2. To determine the neutral and ground wires, you will need a multimeter. As you know, due to phase imbalance, voltage may appear in the neutral wire. Its value usually does not exceed 30V. Set the multimeter to AC voltage mode. Touch the phase wire with one probe, and the other two wires in turn with the second. Where the voltage value is lower, the second wire will be the neutral conductor.
3. If the voltage value is the same, it is necessary to measure the resistance of the ground wire. To do this, it is better to insulate the already defined phase wire to avoid accidental touching it. The multimeter is set to resistance measurement mode. Find a known grounded element, for example, a pipe or battery. If necessary, clean the paint and touch the metal with one multimeter probe, and the other one in turn to the conductors, the purpose of which is unclear. The resistance of the grounding wire in relation to grounded elements should not exceed 4 Ohms, the resistance of the neutral wire will be greater.
4. The resistance measurement may also be unreliable if the neutral is grounded in the panel. In this case, you need to find the grounding conductor connected to the bus inside the panel and disconnect it. After this operation, you need to take a socket with a lamp and connected wires, strip their ends and connect one lamp wire to the phase wire, and the second - alternately to the other two. The lamp will light up when touching the neutral conductor.

If all of the above measures do not lead to the desired result, it is better to contact professional electricians who, using special devices, will call all circuits. Don't forget that this is primarily about safety.

When working with household electrical networks, you need to know how to find phase and zero. The 220 volts we are used to do not appear out of nowhere.

The entire low-voltage network (meaning the value for consumers) is three-phase. The voltage between phases is variable, 380 volts.

For domestic needs, a voltage of 220 volts is used. In order not to go into the trigonometric details of constructing the three phases, it is enough to know the formula: the voltage between phase and zero is equal to the voltage between phases, divided by the square root of Pi. That is, if there are 380 volts between phases, then the voltage between phase and zero will be 380/1.73 = 220 volts.

Why is it necessary to know where the zero is and where the phase is?

Many users of household appliances believe that it makes no difference how to connect electrical appliances to a 220 volt AC network. There is no polarity, the voltage does not change when changing contacts. This is true from the point of view of simply plugging into an outlet.

And if you do the wiring or repair of the electrical network in your home yourself, you need to know exactly where the zero is and where the phase is.

1. When designing electrical panels, single-contact circuit breakers are used. Only the phase starts on them. The zero line remains unopened. Each line is connected with one wire to the phase through a switch, and to the zero line directly;

Important! If you confuse zero and phase with such a connection, using the network will be life-threatening.

2. Lighting devices are powered in the standard way, using single-phase switches. Only the phase wire opens; the neutral wire is always connected to the light fixture. If zero and phase are confused, simply replacing a light bulb can result in electric shock.

Therefore, it is necessary to monitor the phase and neutral wires along the chain from the meter to each consumer.

Several ways to determine phase and zero

Method No. 1, using a tester capable of measuring voltages up to 1000 volts. This is a reliable method, but to check it is necessary to have a properly connected ground wire. It is not available in old designed apartments.

Content:

When performing repair and construction work, an important step is connecting premises and buildings to the power supply system. In this case, in addition to electrical wiring, a large amount of other equipment is installed, including sockets and switches. When making connections, the question quite often arises of how to determine phase and zero, as well as the grounding conductor in the electrical network. Solving this problem does not present any difficulties.

However, ordinary owners of apartments and private houses without special knowledge and experience often cannot solve this problem on their own. It is possible to determine the purpose of each conductor using several simple and accessible methods.

How to determine phase and zero with an indicator screwdriver

The simplest and most common way to accurately determine phase and zero is to use an indicator screwdriver. This operation does not present any difficulties and only requires compliance with a certain algorithm of actions.

When deciding how to determine where the phase is and where the zero is, first of all it is necessary to de-energize the line and turn off the circuit breaker through which the home electrical network is powered. After disconnecting, you should strip the wires being tested, removing approximately 1-2 cm of insulation. Next, the conductors are separated from each other at a safe distance. This must be done to eliminate the possibility of a short circuit due to accidental contact after voltage is applied. After all the preparatory activities, you can begin to determine the phase and zero. You must first turn on the machine and apply voltage to the network.

The tester directly checks the phase and zero as follows. The indicator is pinched between the thumb and middle finger. In this case, do not touch the open, uninsulated part of the screwdriver blade with your fingers to avoid electric shock.

Your index finger should touch the round metal protrusion located at the end of the handle. After this, the tip of the screwdriver is applied to the stripped ends of the conductors. If the tester touches the phase conductor, the LED lights up. Therefore, the second wire is neutral. The neutral wire is detected when the indicator light does not light up initially.

How to determine phase and zero with a multimeter

In addition to an indicator screwdriver, determining phase and zero can be done using a multimeter. In this case, it is also necessary to strip the conductors to be checked. You must first de-energize the electrical network by turning off the machine. This prevents accidental contact between phase and neutral conductors. The wires themselves need to be moved apart a little. After this, the machine should be turned on again.

Next, the multimeter sets the limit value for measuring alternating voltage, which is more than 220 V. Then you need to look at what markings the sockets with the probes of the device have. The probe in the COM socket is not suitable for determining the phase; therefore, the remaining probe, indicated by the symbol V, will be used. Having decided on the probes, you can begin to determine the purpose of the wires.

You need to take the probe, touch it to one of the wires in the socket and look at the readings of the multimeter. When displaying data with a small voltage value (less than 20 V), the wire will be considered phase. If the measuring device shows a zero value, then the wire itself will accordingly be zero.

Any type of multimeter can be used for measurements - with a digital display or a pointer. The accuracy of measurements with a multimeter is much higher than with an indicator screwdriver. When determining phase and zero with a multimeter, it is prohibited to simultaneously touch the phase and ground wires. Such actions may cause short circuits and traumatic burns.

How to determine phase and zero without instruments

Quite often situations arise when an indicator screwdriver and a multimeter are missing, and you need to find out the purpose of the wires so as not to stop electrical installation work. In such cases, you have to solve the problem of determining phase and zero without a device.

The simplest way is to determine the purpose of the wires by their. This technique brings a positive result only when the wiring is carried out in compliance with all technical rules. In this case, the color of the insulation directly indicates the identity of a particular wire.

The ground wire is painted yellow-green, and the neutral conductor is most often blue or dark blue. For the phase conductor, black, white or brown wire is selected. The correct connection can be checked visually, not only in the panel, but also in junction boxes, in the chandelier and other points.

The second way to determine phase and zero involves using a so-called test light. You can use a regular incandescent lamp and two pieces of wire, each 50 cm long. The wire strands are connected to the light bulb and the structure is ready for use. One end of the wire needs to touch the heating pipe, and the other - the wires being tested. If the light comes on when touched, then this wire is a phase wire.

This method at home is considered dangerous due to the high probability of electric shock. It cannot be used when there is extreme voltage in the network. It is safer to use neon bulbs, which allow you to determine the purpose of the wires with equal accuracy.

Many of us have never encountered the search for a phase, others do it all the time, and others need it from time to time. For what? There are all sorts of situations. Here are at least some of them:

1. You need to hang a chandelier that has two, three or more shades.
2. You bought an electrical appliance that requires polarity, and our sockets are not designed for this (and this happens, although rarely).
3. You are repairing the wiring in an apartment or doing wiring in a house, but your wires are still Soviet, all the same color. You don’t seem to need much - just find out how to find phase and zero with the indicator screwdriver that you have.
4. You need to find a bare wire, which is a source of danger (this situation occurs when dismantling buildings, repairs in unfamiliar premises, and it is not possible to turn off all this).

But before we begin our search, let's figure out what we are looking for.

We all know from our school physics course that alternating current flows in our electrical networks. Some even know how variable it is - 50Hz. That is, in one second the charge carriers jerk back and forth fifty times. The graph of voltage and current in the network graphically looks like a sine wave.

The amplitude of the voltage fluctuation is about 310 V. If we pass this current through and rectify it, we get the effective voltage in the network - 220 V. In fact, this is the average value over the entire sine wave, it is obtained by dividing the amplitude by the square root of two.

But then it gets more interesting. Few ordinary people know that Russia has a three-phase power supply. It clearly looks like this: not one power wire comes out of the transformer booth in your neighborhood, but three, and one more, called neutral or zero. The difference between the first three is that the current and voltage sinusoids in them are shifted relative to each other by 2π/3. This means that if in one wire the cycle is in one third, then the second has just begun, and the third has not yet caught up. It is hard to imagine? You can give this picture:

This phenomenon is called phase shift.

One such wire and a neutral are supplied to each apartment, connecting you to the ends of all three windings of your yard transformer and to the ground. However, you must also have a separate land to remove static from the housings of household appliances.

From this figure you can understand that the statement “there is no voltage at zero” is not entirely true. It won’t be there when everyone in their apartments has electrical appliances operating on three phases - then the load on them will be symmetrical. But few people would think of installing electric motors from industrial units in an apartment, and the load is rarely symmetrical. Therefore, there is always some voltage in the neutral wire.

Phase search

Currently, we can easily determine the phase wire using special devices. This simple operation can be done by anyone. We will do this in two ways - using an indicator screwdriver and a multimeter. And in the end we’ll talk about whether it’s possible to find phase and zero without instruments and how to do it.

How to determine with an indicator screwdriver

An indicator screwdriver is a device with a transparent handle, inside of which there is a capacitor bulb, and the end of the handle is a conductor. It looks like this:

The operating principle of this indicator is simple. You insert a screwdriver into the socket, and if you hit the phase and press the contact plate on the handle, you increase the capacitance of the capacitor at the expense of your body - the neon light comes on. You will find the phase easily. But zero, even if there is voltage in it, is not. It never exceeds 60 V, and below this threshold the indicator screwdriver will not show anything. This is not necessary: ​​when the light bulb lights up only when it comes into contact with a phase, such a screwdriver is the best phase determiner.

More advanced versions of indicators (with LED, sound signal and battery-powered) are not helpful here: they will also show lower voltage. If you show it, then it will be with size. And to determine this value, we’d better use a multimeter. But it is best to use such indicators to find hidden wiring. There are also more advanced devices for this purpose. Some of them react to the field created by alternating current, others - to the metal in the wall. But all these devices have another area of ​​application, which is beyond the scope of this topic.

Looking with a multimeter

It is not difficult. To begin with, let's set the switch of your tester to a function (either this sector will be called ACV, or it will be V~) with a limit above 220 V. For some it will be 500, for others 800. Testers are different. We insert the black probe into the common socket (COM is written next to it), and the red one into the socket for measuring current, voltage and resistance. You don’t need to put it in a socket for working with a ten-amp current; you most likely don’t have it there. Then we insert both second ends of the probes into the holes of the socket. If it is working, the display will show your voltage value - from 220 to 230 V.

It remains to find out where the phase is. We insert the red probe into one of the holes in the socket, and either hold the black one with our fingers or connect it to the ground, for example, to the central heating radiator (find the place where the paint has fallen off, or clean it off a little). If you hit the phase, then the display will show an effective voltage of about 220 V. And if you hit zero, then you will not see more than 60 V (more often - no more than 30 V).

Determining phase and neutral wires for installing a three-phase socket

This situation can happen in the house with Soviet-made electric stoves. You have five wires, they are the same color, the socket will be asymmetrical, and we need to know exactly where the three phases are, where the zero is, and where the ground is. And this is important - all types of three-phase sockets are asymmetrical.

Here you need a little help. If we have 220 V between one phase and the neutral, then between two phases with a shift of 120 degrees (2π/3) 220 will need to be multiplied by the square root of three, and we will get an effective voltage of 380 V.

So we stock up on colored markers, paper and pen, and start solving the puzzle. We mark the insulation with markers of different colors, look for phases in the same way as in a regular outlet, and write down the results on a piece of paper. It will be relatively simple to distinguish three phases. And then you need to find zero and ground. If the grounding is done correctly, the voltage in it will be zero, and in the neutral there will be several tens of volts.

To control, we measure the voltage between phases. It should be 380 V, and between zero and each phase there should be 220 V.

Another interesting use of a multimeter

The tester can be used to search for hidden wiring in an apartment if it is energized. Usually this can be done without it, if the wiring is carried out according to the rules. In this case, you can navigate by distribution boxes. It’s worse if you got the apartment after a home-grown European-quality renovation, when everything unnecessary was simply covered with plaster.

To detect wiring you will need a tester and a KP303 transistor (another field effect one is also possible).

Set the switch to somewhere around 200 kOhm. Insert the probes into the standard position (COM and universal socket) and connect their ends to the source and drain of the transistor. A wire antenna can be wound around the gate. If there is a live wire in the wall, it will create an electromagnetic field, albeit a small one, which will change the internal resistance of the transistor.

If there are no devices

What to do if you have neither a tester nor an indicator screwdriver? How to determine phase and zero without instruments? It turns out that this is possible.

True, before you do this, look at your shield: maybe you won’t have to do anything. If the house is new and the wiring in it is done according to the rules, then the wires can be identified by color. So, zero is made blue, phase is any other color, and grounding is yellow-green. Please also note for circuit breakers(like small switches): they must be in phase. If you unscrew the socket and see the ground in its place, then, most likely, the electrician has not confused the zero with the phase either.

In general, there are household methods for diagnosing wiring, here are some of them:

1. using a probe;
2. using potatoes;
3. using old fuses and pliers;
4. "with bare hands.

For obvious reasons, we will not discuss the last three.

Using a probe

A probe is an incandescent lamp in a socket with two wires connected. It is not entirely ethical to recommend this method of verification: the instructions prohibit this method. You should not use it in situations where you do not know how many phases are carried into the room and where everything is turned on and off.

But sometimes you have to use a probe. For example, to distinguish zero from grounding in the absence of sockets (we are considering a situation where sockets are not installed, and three wires stick out from the wall).

Recently, three-wire wiring has been installed in residential premises. If electricians have neglected the color rules, you can distinguish where the zero is and where the ground is using a probe. To do this, you need to turn off one of the zeros in the panel, if you don’t know which one is real, and check the functionality of the future outlet. If you disconnect the zero, then the sockets will not work and the light bulb will not light up - the apartment grounding is not connected to the circuit. And when the ground is turned off, the light bulb will work.

What not to do

In fact, you already know the basic rules of working with wiring., but I would like to repeat some.

1. Do not grab the multimeter probes by their exposed parts. I hope there is no need to explain why.
2. Some citizens have a habit of looking for hidden wiring with their bare hands. If you are one of these people, there is no point in dissuading you. But I can give you some advice: do this with the back of your hand. If you get an electric shock, you will bounce off the wall, otherwise you risk not letting go of the exposed wire due to a cramp.
3. Sometimes it is possible to measure resistance rather than voltage to indicate zero and phase. Be careful: when operating the tester in this mode, do not short-circuit the phase to ground, as a short circuit may occur.

In order not to find yourself in a situation where you have to sort the wires in the future, I would like to advise you to label them. In the future, it will be easier for you to repair and connect electrical appliances. Well, be sure to get an indicator screwdriver. It costs a penny, but is a useful tool for the household. Believe me, the order in your panel and the security of the power supply to your home are worth a lot.

So, imagine this situation - you need to connect a new outlet, but for some reason you do not know which of the wires on the output is phase and which is neutral. The situation is further complicated by the fact that there was neither an indicator screwdriver nor a multimeter at hand, which would allow you to quickly find which wire the voltage is passing through. Next, we will tell readers how to determine phase and zero without instruments!

Method No. 1 – Visual designation

The first and most reliable way to independently determine where the phase and zero are without a tester is to examine the color of the insulation of each conductor, based on which you can draw a conclusion.

The fact is that it is designed precisely so that you can find out which of the conductors is neutral and which is phase without instruments. To make it clearer for you and to be able to correctly determine the phase and zero, we provide a table with existing standards:

As you can see, insulation can be of different colors, so it is better to remember that 0 is always blue, and ground is yellow-green (or only yellow/green). As a rule, the remaining third core is the phase that you need to determine. If there is no color marking, which is no exception, you can find phase and zero without a tool in other ways, which we discussed below!

Method No. 2 – Do a check

The second idea to determine without a tester where the phase wire is and where the neutral wire is in the socket is that you need the most available tools. Everything is very simple, you just need to find an incandescent lamp with a socket and two pieces of stranded wire, about 50 centimeters long.

The conductors are connected to the corresponding connectors of the cartridge, one conductor is attached to the heating pipe, stripped to a metallic color, and the second one needs to “probe” the conductors that interest you. The light will light up if you touch the phase contact. In this simple way you can quickly find out, without instruments, where the phase and zero are.

Please note that this search option without instruments is dangerous and can cause electric shock. Be careful when determining the voltage and be careful not to touch the exposed wire with your hand!

A simple sample made from improvised means

If you don’t have an incandescent lamp on hand, you can use a neon light bulb to assemble a homemade tester, which will also allow you to determine the polarity. The control scheme will look like this:

Method No. 3 – Potatoes to the rescue!

A funny, but still effective idea that allows you to determine phase and zero without an indicator, multimeter or other tester. All you need is a potato, 2 wires of 50 cm each and a 1 MOhm resistor. You can find the voltage using the method described above. The end of the first conductor is connected to the pipe, the second end is inserted into the cut of the potato, as shown in the photo. As for the second wire, one end of it needs to be inserted into the same section, at the maximum possible distance from the already inserted wire, and with the second you will feel those terminals on which you need to find phase and zero without instruments. The definition is as follows:

• If a slight darkening has formed on the cut, this is a phase conductor;
• No reaction occurred - you “found” zero.

It should immediately be noted that in this case the determination should occur with a short delay of time when the vein comes into contact with the potato cut. You must touch the wire to the potato and wait about 5-10 minutes, after which the result will be visible!

Visual video lesson on how to determine polarity without instruments with your own hands

Using a similar technique, you can determine the polarity of contacts in a DC circuit. To do this, two wires are lowered into a cup of water and if bubbles begin to form near one of them, as shown in the photo below, it means that this is a minus and, accordingly, the second wire is a plus.