How to determine phase and zero

When installing sockets and light switches, connecting household electrical appliances, it becomes necessary to determine the assignment of the conductors of the wiring. How to determine the phase and "zero", as well as the ground conductor? This task, which is not difficult for professional electricians, sometimes confounds those who have little knowledge of the rules for the installation of electrical networks. Let's try to understand this question.

Device of household electrical networks

Household electrical networks at the input to the switchboard have a line voltage of 380 V AC.The wiring in the apartments, with rare exceptions, has a voltage of 220 V, since it is connected to one of the phases and the zero conductor. In addition, properly installed household wiring must be necessarily grounded. In the houses of the old building, a grounding conductor may not exist. Thus, when installing wiring and electrical appliances, you need to know the purpose of each of the two or three wires.

You should also know the rules for connecting different devices. When installing a standard outlet, the connection of the phase and neutral conductors is made to the terminals in any order, and the ground wire, if any, is connected to a copper or brass bus. The switch is connected to a phase wire so that when it is disconnected in the lamp holder there is no voltage - this will ensure safety when changing lamps. Complex household appliances in a metal casing must be connected in accordance with the marking of the wires, otherwise the safety of their use is not guaranteed.

Instruments and tools

Before proceeding with the wiring work and determine the phase and zero in the wiring, it is necessary to prepare the necessary instruments and tools:

• Multimeter switch or digital;
• Indicator screwdriver or tester;
• Marker;
• Combination pliers;
• Knife for stripping insulation.

You also need to find out where the protective equipment is located: automatic switches or plugs, RCDs. Usually, they are installed in the switchboard on the site or at the entrance to the apartment. All operations for connecting electrical equipment and stripping the wires must be carried out with the automatics switched off!

Rules for working with the tester and multimeter

The phase check with the indicator screwdriver is carried out as follows: the screwdriver is clamped between the thumb and middle finger, without touching the non-insulated part of the tip. The index finger is placed on the metal snap from the end of the handle. A bare end touches the exposed ends of the wires, when touched to the phase conductor, the LED lights up.

Multimeter measure the voltage between the conductors. For this purpose, the instrument is set to the AC measuring limit with a "~ V" or "ACV" icon and a value greater than 250 V( typically 600, 750 or 1000 V limit for digital instruments).The probes simultaneously touch the two conductors and determine the voltage between them. In households it must be 220V ± 10%.

Sometimes it is necessary to measure resistance to determine the ground conductor. To do this, set the measuring limit to "Ω" or to the ring icon on the multimeter.

Visual method for determining

If the wiring is carried out according to all rules, the phase, zero and ground conductor can be determined by the color of the insulation. The grounding has a two-color yellow-green color, the insulation of the neutral wire is blue or blue, and the phase wire can be white, black or brown. You can verify the correct connection by visual inspection, while checking that the color of the insulation is not only in the shield, but also in the junction boxes.

Sequence of visual inspection

1. Open the cover and inspect the circuit breakers. Depending on the design load, their number may be different. Only phase or phase and neutral wire can be connected through the machines. The grounding conductor is always connected directly to the bus. Check the conformity of the color coding of all wires.
2. If the color of the insulation of the cable leaving the apartment meets the rules, open all the junction boxes and inspect the twists. In them, the colors of the insulation of the zero and the ground wire also should not be confused.
3. Switches are connected to the phase in junction boxes. Often, the installation is carried out with a two-wire cable having different insulation colors, for example, white and white-blue. This should not embarrass you.
4. If the installation is carried out in full accordance with the color of the insulation, it is sufficient to check the phase wire with the aid of an indicator screwdriver.

Determining phase and zero in a two-wire network

If your wiring is done without a ground conductor, you only need to find the phase wire. This is most easily done with the help of an indicator screwdriver.

1. Disconnect the circuit breaker and clean the insulation of the wires 1-1.5 cm apart with a knife. Distinguish them by a distance, excluding accidental contact of wires.
2. Turn on the circuit breaker. Use the indicator screwdriver to alternately touch the stripped ends of the wires. A glowing diode will indicate the phase wire.
3. Mark it with a marker or colored electrical tape, disconnect the circuit breaker and make the necessary connections.
4. When connecting the lighting devices, it is also necessary to make sure that the switch is connected to the phase conductor, otherwise, when changing the bulbs, it will not be enough to disconnect the switch, each time completely disconnecting the apartment by switching off the machine.

Phase, zero and ground wire detection

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

1. Determine the phase wire using the indicator screwdriver as described above and mark it with a marker.
2. A multimeter is required to determine the ground and ground wires. As you know, because of the distortion of the phases in the zero wire, voltage may appear. Its value usually does not exceed 30V.Set the multimeter to AC voltage measurement mode. With one probe, touch the phase wire, the second one alternately to the other two wires. Where the voltage value is less, the second wire will be the zero conductor.
3. If the voltage value is the same, measure the resistance of the ground wire. To do this, a certain phase conductor is better insulated to avoid accidental contact with it. The multimeter is put into the resistance measurement mode. Find a known grounded element, for example, a pipe or a battery. If necessary, clean the paint and touch with one probe of the multimeter to the metal, and the other in turn to the conductors, whose purpose is unclear. The resistance of the ground wire to grounded elements should not exceed 4 ohms, the resistance of the zero wire will be greater.
4. Measurement of the resistance may also be unreliable if the neutral is grounded in the shield. In this case, you need to find the grounding conductor connected to the bus inside the flap and disconnect it. After this operation it is necessary to take a cartridge with a lamp and connected wires, to clean their ends and connect one wire of the lamp to the phase conductor, and the second - alternately to the other two. The lamp will light when touching the zero conductor.

If all of the above measures did not lead to the desired result, it is better to turn to professional electricians who by means of special devices will make the removal of all circuits. Do not forget that we are talking, first of all, about security.