Designation of phase and zero on old circuits. Color marking of wires. Why do I need a protective conductor in euro sockets

There are, in fact, not many different types of conductors and their connections. In the electric power industry, a distinction is made between supply and protective conductors. Some have heard such words as "zero" and "phase" wire. However, this is where questions arise. How to determine zero and phase in a real network?

What are the conductors in the socket?

You can deal with the question "what is phase and zero" without delving into the wilds of finding out the structure, advantages and disadvantages in three-phase or five-phase circuits. You can actually disassemble everything on your fingers, revealing the most ordinary home socket, which is placed in an apartment or a private house ten or fifteen years ago. As you can see, this socket is connected to two wires. How to determine zero and phase?

How do wires work in an outlet and why are they needed?

As you can see, there are certain differences between workers and zero. What is the designation of phase and zero? A bluish or blue color is the color of the phase wire, zero is indicated by any other colors, except, of course, blue flowers. It can be yellow, green, black and striped. The current does not flow. If you take it and do not touch the worker, then nothing will happen - there is no potential difference on it (in fact, the network is not ideal, and there may still be a small voltage, but it will be measured at best in millivolts). But with a phase conductor, this will not work. Touching it can result in electrical shock, even fatal. This wire is always energized, current flows to it from generators and transformers and stations. It must always be remembered that in no case should you touch the working conductor, since a voltage of even a hundred volts can be fatal. And in the socket is two hundred and twenty.

How to determine zero and phase in this case? In the socket, designed according to European standards, there are three conductors at once. The first is phase, which is energized and painted in a variety of colors (with the exception of blue shades). The second is zero, which is absolutely safe to touch and is painted in. But the third wire is called zero protective. It is usually colored yellow or green. It is located in sockets on the left, in switches - from below. The phase wire is on the right and top, respectively. Given such colors and features, it is easy to determine where the phase is, and where is zero, and where is the protective neutral wire. But what is it for?

Why do I need a protective conductor in euro sockets?

If the phase is designed to supply current to the outlet, zero - to lead to the source, then why do European standards regulate another wire? If the equipment that is connected is working properly, and all wiring is in working order, then the protective zero will not take part, it is inactive. But if suddenly somewhere there is either an overvoltage or a short circuit on some parts of the devices, then the current enters places that are usually without its influence, that is, not connected either to the phase or to zero. A person can simply feel an electric shock on himself. In the worst situation, you can even die from this, as the heart muscle can stop. This is where the protective neutral wire is needed. He "takes" the current short circuit and directs it to the ground or to a source. Such subtleties depend on the design of the wiring and the characteristics of the room. Therefore, you can safely touch the equipment - there will be no electric shock. The thing is that current always flows along the path of least resistance. In the human body, the value of this parameter is more than one kiloOhm. In a protective conductor, the resistance does not exceed a few tenths of one ohm.

Determining the purpose of conductors

How to determine zero and phase? Everyone has come across these concepts in one way or another. Especially when you need to fix the outlet or do the wiring. Therefore, it is necessary to understand exactly where which conductor is. But how to determine zero and phase? It must be remembered that all manipulations of this kind with electricity are dangerous. Therefore, in case of uncertainty in their actions, it is better to consult a specialist. If you already approach the outlet and the wires in it, then you must first completely de-energize the entire apartment. At a minimum, it can save health and life. As mentioned earlier, usually the designation of phase and zero is done using coloring. With proper labeling, it will not be difficult to distinguish them. Black (or brown) - the color of the phase wire, zero usually has a bluish or bluish tint. If a European standard socket is installed, then the third (protective zero) is green or yellow. What if the wiring is one-color? As a rule, in this case, at the ends of the wires there are usually special insulating tubes that have the necessary color marking. They are called "cambric".

Determining conductors with a special screwdriver

How to determine zero and phase? To do this, it is most convenient to buy a special indicator screwdriver. The handle of such a device is made of translucent or transparent plastic. Built-in diode glowing light bulb. Top part This screwdriver has a metal one. How to determine zero and phase by this method?

The procedure for performing work when measuring with an indicator screwdriver:

• de-energize the apartment;
• we clean slightly the ends of the wires;
• we separate them to the sides in order not to accidentally cause a short circuit by contacting the phase and zero;
• turn on the switch and supply current to the apartment;
• we take a screwdriver by the handle, which has a dielectric coating;
• put your finger (thumb or index) on the contact, which is located on the back of the outlet;
• touch the working end of the indicator to one bare conductor;
• carefully observe the reaction of the screwdriver;
• if the diode caught fire, then we can state with confidence that;
• by elimination, we understand that the remaining conductor is zero.

The indicator screwdriver reacts to the presence of voltage. Naturally, it is not in the neutral wire. However, there is significant disadvantage such a method. By using indicator screwdriver it’s impossible to understand how to determine: phase, zero, earth - where is what in the case of a European outlet.

Method for determining phase and zero using a voltmeter

If the wires are not painted in the appropriate colors, and there is no indicator screwdriver at hand, then you can go the other way. We need a voltmeter (multimeter, tester). It is necessary to set it to the required range - over two hundred volts alternating current. How can a tester determine the phase? We take one conductor that departs from the device (indicated by V). We attach it to a previously de-energized conductor (any). Then we apply current (turn on the switch). And just fix what the device display shows. After all of the above, turn off the power again and transfer the tester clamp to another conductor. If there is nothing on the display, then this means that we have either a zero or a grounding protective neutral wire in front of us. However, you can use another method that answers the question: "How to determine zero and phase, as well as grounding." To do this, we de-energize the apartment again, fix the V clamp on one of the wires. We also throw the second on any of the three conductors. The voltage is turned on. If the arrow does not move, then you have chosen zero and protective. Accordingly, the voltage must be turned off again and the position of the V terminal must be changed (throw it onto another previously unused conductor). We turn on the current again and take the appropriate measurements. Then we carry out the same operation, but again we change the conductor. Now we need to check the results. If the first digit turned out to be larger, it means that we measured the voltage between the phase conductor (on which the V terminal hung) and zero. Accordingly, the second wire will be a protective ground. This method is based on measuring the potential difference.

Exotic ways to determine the phase and zero in the wiring

There are also folk methods", which do not imply the presence of any special devices. They can only be used in the most extreme cases, as they are associated with increased danger to health and life. For example, the potato method. To do this, a freshly cut piece of potato is put on previously de-energized conductors. It is necessary to prevent the wires from touching each other so that there is no short circuit between them. Then, literally for a couple of seconds, voltage is applied and they look at the potatoes. If one section near the wire turns blue, then a phase is connected to it.

The vast majority of cables different colors lived insulation. This was done in accordance with GOST R 50462-2009, which sets the l n marking standard in electrics (phase and zero wires in electrical installations). Compliance with this rule guarantees fast and safe work masters at the big industrial facility, and also allows you to avoid electrical injury during self-repair.

Variety of colors for electrical cable insulation

The color coding of wires is diverse and varies greatly for grounding, phase and neutral conductors. To avoid confusion PUE requirements regulate what color of the ground wire to use in the power panel, what colors must be used for zero and phase.

If installation work carried out by a highly qualified electrician who knows modern standards for working with electrical wires, you do not have to resort to using an indicator screwdriver or a multimeter. The purpose of each cable core is deciphered by knowing its color designation.

Ground wire color

From 01/01/2011, the color of the ground (or neutral) conductor can only be yellow-green. This color marking of wires is also observed when drawing up diagrams on which such cores are signed in Latin letters PE. Not always on cables, the coloring of one of the cores is intended for grounding - usually it is done if there are three, five or more cores in the cable.

PEN-wires with combined "ground" and "zero" deserve special attention. Connections of this type are still often found in old buildings, in which electrification was carried out according to outdated standards and has not yet been updated. If the cable was laid according to the rules, then the blue color of the insulation was used, and yellow-green cambric was put on the ends and joints. Although, you can also find the color of the ground wire (grounding) exactly the opposite - yellow-green with blue tips.

The ground and neutral conductors may differ in thickness, often it is thinner than the phase ones, especially on cables that are used to connect portable devices.

Protective grounding is mandatory when laying lines in residential and industrial premises and is regulated by the PUE and GOST 18714-81 standards. The zero ground wire should have as little resistance as possible, the same applies to the ground loop. If all installation work is done correctly, then grounding will be a reliable protector of human life and health in the event of a power line malfunction. As a result, the correct marking of cables for grounding is critical, and grounding should not be used at all. All new houses are wired according to the new rules, and the old ones are queued for replacement.

Colors for neutral wire

For "zero" (or zero working contact), only certain wire colors are used, also strictly defined by electrical standards. It can be blue, blue or blue with a white stripe, and regardless of the number of cores in the cable: a three-core wire in this regard will not differ in any way from a five-core one or with more big amount conductors. In electrical circuits, “zero” corresponds to the Latin letter N - it participates in closing the power supply circuit, and in circuits it can be read as “minus” (phase, respectively, is “plus”).

Colors for phase conductors

These electrical wires require special care and "respectful" handling, as they are current-carrying, and careless touch can cause severe injury. electric shock. The color marking of wires for connecting the phase is quite diverse - you cannot use only colors adjacent to blue, yellow and green. To some extent, it is much more convenient to remember what the color of the phase wire can be - NOT blue or blue, NOT yellow or green.

On electrical diagrams, the phase is denoted by the Latin letter L. The same marking is used on wires if color marking is not used on them. If the cable is designed to connect three phases, then the phase conductors are marked with the letter L with a number. For example, to create a diagram for three-phase network 380 V used L1, L2, L3. Even in electrics, an alternative designation is accepted: A, B, C.

Before starting work, you need to decide how the combination of wires will look in color and strictly adhere to the chosen color.

If this question was thought out at the stage preparatory work and taken into account when drawing up wiring diagrams, you should purchase required amount cables with conductors of the required colors. If still desired wire is over, you can manually mark the cores:

• ordinary cambric;
• shrink tubes;
• tape.

About wire color marking standards in Europe and Russia, see also in this video:

Manual color marking

It is used in cases where during installation it is necessary to use wires with conductors of the same color. It also often happens when working in old houses, in which the wiring was done long before the advent of standards.

Experienced electricians, so that there is no confusion during further maintenance of the electrical circuit, used kits that allow you to mark phase wires. This is allowed and modern rules, because some cables are made without color-letter designations. The place of use of manual marking is regulated by the norms of the PUE, GOST and generally accepted recommendations. It is attached to the ends of the conductor, where it connects to the bus.

Marking two-wire wires

If the cable is already connected to the network, then to search phase wires in electricians, a special indicator screwdriver is used - in its case there is an LED that glows when the sting of the device touches the phase.

True, it will be effective only for two-wire wires, because if there are several phases, then it will not be able to determine where which indicator is. In this case, you will have to disconnect the wires and use a continuity.

Standards do not oblige to make such markings on electrical conductors along their entire length. It is allowed to mark it only at the joints and connections of the necessary contacts. Therefore, if it becomes necessary to apply labels on electrical cables without designations, you need to purchase materials in advance for marking them manually.

The number of colors used depends on the scheme used, but the main recommendation is still there - it is desirable to use colors that exclude the possibility of confusion. Those. do not use blue, yellow or green labels for phase wires. IN single-phase network, for example, the phase is usually indicated in red.

Three-core wire marking

If you need to determine the phase, zero and ground in three-wire wires, then you can try to do this with a multimeter. The device is set to measure AC voltage, and then gently touch the phase with the probes (it can be found and indicator screwdriver) and in series the two remaining wires. Next, you should remember the indicators and compare them with each other - the “phase-zero” combination usually shows a greater voltage than “phase-ground”.

When the phase, zero and earth are determined, then marking can be applied. According to the rules, a yellow-green colored wire is used for grounding, or rather a core with such a color, so it is marked with electrical tape of suitable colors. Zero is marked, respectively, with blue electrical tape, and the phase is any other.

If, during preventive work, it turned out that the marking was outdated, it is not necessary to change the cables. Replacement, in accordance with modern standards, is subject only to electrical equipment that has failed.

As a result

Proper wiring is a must. quality installation electrical wiring during work of any complexity. It greatly facilitates both the installation itself and the subsequent maintenance of the electrical network. In order for electricians to “speak the same language”, mandatory standards for color-letter marking have been created, which are similar to each other even in different countries. In accordance with them, L is the designation of the phase, and N is zero.

Conductor insulation color coding is important for faster and faster correct installation electrical distribution devices, ease of repair and elimination of errors. The colors of the wires in the electrician are regulated normative documents (PUE and GOST R 50462-2009).

Why color coding of wires and cables is needed

Installation and maintenance work in electrical installations related not only to reliability, but also to safety. Full error elimination is required. For these purposes, a system of color designations for core insulation has been developed, which determines what color the wires are phase, zero and earth.

According to the PUE, the following colors of current-carrying conductors are allowed:

• red;
• brown;
• black;
• gray;
• white;
• pink;
• orange;
• turquoise;
• purple.

The list below contains many wire color options, but there are not several colors that are used only to designate neutral and protective wires:

• blue color and its shades- working neutral wire ( neutral - N);
• yellow with green stripe– protective earth ( PE);
• yellow-green insulation with blue markings on the ends of the cores- combined ( PEN) conductor.

It is allowed to use conductors with green insulation with a yellow stripe for grounding, and for combined conductors of blue insulation with yellow-green marks at the ends.

The colors must be the same in each circuit within the same device. Branch circuits must be carried out with the same colored conductors. The use of insulation without differences in shades indicates a high installation culture and greatly facilitates further maintenance and repair of equipment.

Phase color

In cases where the installation of the electrical installation is carried out using rigid metal tires, the tires are painted with indelible paint in the following colors:

• yellow - phase A ( L1);
• green - phase B ( L2);
• red - phase C ( L3);
• blue - zero bus;
• longitudinal or oblique stripes of yellow and green- ground bus.

The color of the phases must be preserved within the entire device, but not necessarily on the entire surface of the tire. It is allowed to mark the phase designation only at the connection points. On the painted surface, you can duplicate the color with the symbols “ ZhZK” to paint the corresponding colors.

If the tires are not available for inspection or work when voltage is present on them, then it is allowed not to paint them.

The color of the phase wires connected to the rigid busbars may not match them in color, since the difference in the accepted designation systems for flexible conductors and rigid stationary distribution busbars is visible.

Neutral color

What color is the neutral wire, standards stipulate GOST, therefore, when looking at the installation power plant there should be no question blue wire- this is because the blue color and its shades ( blue) are taken to denote the neutral ( working ground ).

Other neutral core colors are not permitted.

The only acceptable use of blue and blue insulation is the designation of a negative pole or midpoint in circuits direct current. You can't use this color anywhere else.

Ground wire color code

Regulations specify what color the earth wire is in electrical installations. This is a yellow-green wire, the color of which stands out well from the rest of the wires. It is allowed to use wire with yellow insulation and a green stripe on it, or it can be green insulation with a yellow stripe. No other color of ground wire is permitted, nor are green/yellow conductors permitted to be used in circuits where voltage is present or may be energized.

The listed marking rules are observed in the countries of the post-Soviet space and in the EU countries. Other states mark the cores in a different way, which can be seen on imported equipment.

Basic colors for marking abroad:

• neutral - white, gray or black;
• protective earth- yellow or green.

The standards of a number of countries allow the use as protective earth bare metal without insulation.

Ground wires are switched on prefabricated non-insulated terminals and interconnect all metal parts of the structure that do not have reliable electrical contact with each other.

Coloring in the network 220V and 380V

Installation of one- and three-phase electrical networks facilitated if the wiring is done with multi-colored wire. Previously, a flat two-core cable was used for single-phase apartment wiring. white color. During installation and repair, in order to eliminate errors, it was necessary to ring each core separately.

Production of cable products with coloring of cores different colors reduces labor intensity. To designate phase and zero in single-phase wiring, it is customary to use the following colors:

• red, brown or black- phase wire;
• other colors ( preferably blue) - neutral wire.

Phase marking in a three-phase network is slightly different:

• red ( brown) - 1 phase;
• black - 2 phase;
• grey ( white) - 3 phase;
• blue ( blue) – working zero ( neutral)
• yellow-green - grounding.

Cable production domestic production corresponds to the core color standard, so the multi-phase contains differently colored cores, where the phase is white, red and black, zero - blue, and the earth yellow-green conductors.

When servicing networks mounted on modern standards, you can accurately determine the purpose of the wires in the junction boxes. If there is a bundle of multi-colored wires, the brown one will necessarily be phase. The neutral wire has no branches and breaks. The exception is taps to multi-pole switching devices with a complete opening of the circuit.

Coloring in DC networks

For DC networks, it is customary to mark the conductors connected to the positive pole in red, to the negative - in black or blue. In bipolar circuits, blue-tinted insulation is used to mark the midpoint ( zero) nutrition.

There are no standards for color markings in multi-voltage circuits. What color are the plus and minus wires, what voltage is in them - this can only be determined by the manufacturer of the device, which is often given in the documentation or on one of the walls of the structure.

Example: computer power supply or automotive wiring.

Automotive wiring is characterized by the fact that in it the circuits with a positive voltage of the on-board network are red or its shades (pink, orange), and those connected to ground are black. The rest of the wires have a specific color, which is determined by the car manufacturer.

Letter designation of wires

Color marking can be supplemented with letters. Partially, the symbols for designation are standardized:

• L( from the word Line) - phase wire;
• N( from the word Neutral) - neutral wire;
• PE ( from a combination of Protective Earthing) - grounding;
• “+” – positive pole;
• “-” – negative pole;
• M is the midpoint in DC circuits with bipolar power.

To designate the connection terminals, use special character, which is applied to the terminal by stamping or to the body of the device in the form of a sticker. The ground symbol is the same for most countries in the world, which reduces the likelihood of confusion.

In multi-phase networks, the symbols are supplemented by the phase serial number:

• L1 is the first phase;
• L2 - second phase;
• L3 is the third phase.

There is marking according to old standards, when the phases are indicated by symbols A, B and C.

Deviation from the standards is combined system phase designations:

• La is the first phase;
• Lb is the second phase;
• Lc is the third phase.

In complex devices, there may be additional designations characterizing the name or number of the circuit. It is important that the markings of the conductors match throughout the entire circuit where they participate.

Letter designations are applied with indelible, clearly visible paint on the insulation near the ends of the cores, on segments PVC insulation or .

Connection terminals may have printed signs that indicate the circuits and polarities of the power supply. Such signs are made by paint, stamping or etching, depending on the material used.

To facilitate the installation of electrical wiring, the cables are made with multi-colored wire markings. Installation of a lighting network and power supply to sockets involves the use of a cable with three wires.

The use of this color system significantly reduces the time for repairs, connecting sockets and. Also this scheme minimizes the requirements for the qualification of the installer. This means that almost any adult man is able to carry out, for example, the installation of a lamp.

In this article, we will look at how ground, zero and phase are designated. As well as other color markings of wires.

Ground Color

The color of the ground wire, "ground" - almost always marked in yellow-green, windings are less common as completely yellow color, and light green. The wire may be marked "PE". You can also find green-yellow wires marked "PEN" and with a blue braid at the ends of the wire at the attachment points - this is grounding combined with neutral.

In the switchboard (RSH) it is worth connecting to the ground bus, to the body and the metal door of the shield. Concerning junction box, then there the connection goes to the ground wires from the lamps and from the ground contacts of the sockets. The earth wire does not need to be connected to the RCD (device protective shutdown), in this regard, RCDs are installed in houses and apartments, since usually electrical wiring is carried out with only two wires. Grounding designation on the diagrams:

Conventional ground(1) Clear ground(2) Safety ground(3) Chassis ground(4) DC ground(5)

Color zero, neutral

Zero wire - must be of blue color . In the switchboard, it must be connected to the zero bus, which is indicated by the Latin letter N. All blue wires must be connected to it. The bus is connected to the input by means of a meter or directly, without additional installation machine. In the distribution box, all wires (except for the wire from the switch) of blue color (neutral) are connected and do not participate in switching. To the sockets, the blue “zero” wires are connected to the contact, which is indicated by the letter N, which is marked on the back of the sockets.

Phase color

The designation of the phase wire is not so clear. It can be either brown, or black, or red, or other colors. except blue, green and yellow. In the apartment switchboard, the phase wire coming from the load consumer is connected to the bottom contact circuit breaker or to RCD. In the switches, the phase wire is switched, during shutdown, the contact closes and voltage is supplied to consumers. In phase sockets, the black wire must be connected to the contact, which is marked with the letter L.

How to find ground, neutral and phase in the absence of a designation

Letter and number wire markings

The first letter "A" denotes aluminum as the core material, in the absence of this letter, the core is copper.

The letters "AA" stand for stranded cable with an aluminum core and an additional braid from it.

"AC" is indicated in the case of an additional lead braid.

The letter "B" is present if the cable is waterproof and it has an additional double-layer steel braid.

"Bn" cable braid does not support combustion.

"B" PVC sheath.

"G" does not have a protective shell.

"g" (lowercase) naked waterproof.

"K" control cable wrapped with wire under the top sheath.

"R" rubber sheath.

"HP" non-flammable rubber sheath.

Wire colors abroad

The color marking of wires in Ukraine, Russia, Belarus, Singapore, Kazakhstan, China, Hong Kong and in the countries of the European Union is the same: Ground wire - Green-yellow

Neutral wire - blue

phases are marked with different colors

The neutral designation is black in South Africa, India, Pakistan, England, but this is the case with old wiring.

currently neutral blue.

In Australia, it can be blue and black.

In the USA and Canada it is designated as white. Also in the USA you can find gray markings.

The ground wire is yellow, green, yellow-green everywhere, and in some countries it may be without insulation.

Other wire colors are used for phases and may be different, except for the colors indicating other wires.

And in everyday life we ​​use, as a rule, single-phase. This is achieved by connecting our wiring to one of the three phase wires (Figure 1), moreover, which phase comes to the apartment for us, for further consideration of the material, is deeply indifferent. Since this example is very schematic, the physical meaning of such a connection should be briefly considered (Figure 2).

Electric current occurs when there is a closed electrical circuit, which consists of the winding (Lт) of the substation transformer (1), the connecting line (2), the electrical wiring of our apartment (3). (Here the designation of the phase is L, zero is N).

Another point is that in order for current to flow through this circuit, at least one consumer of electricity Rn must be turned on in the apartment. Otherwise, there will be no current, but the VOLTAGE on the phase will remain.

One of the ends of the winding Lt at the substation is grounded, that is, it has electrical contact with the ground (Zml). The wire that comes from this point is zero, the other is phase.

This implies another obvious practical conclusion: the voltage between "zero" and "ground" will be close to zero (determined by the ground resistance), and "ground" - "phase", in our case 220 Volts.

Moreover, if hypothetically ( In practice, this cannot be done!) ground the neutral wire in the apartment by disconnecting it from the substation (Fig. 3), the voltage "phase" - "zero" we will have the same 220 Volts.

What is phase and zero figured out. Let's talk about grounding. The physical meaning of it, I think, is already clear, so I propose to look at it from a practical point of view.

If for some reason an electrical contact occurs between the phase and the conductive (metal, for example) body of the electrical appliance, voltage appears on the latter.

When this body is touched, an electric current can flow through the body. This is due to the presence of electrical contact between the body and the "ground" (Fig. 4). The lower the resistance of this contact (damp or metal floor, direct contact building structure with natural grounding conductors (heating batteries, metal water pipes) the more danger you face.

The solution to this problem is to ground the case (Figure 5), while dangerous current"leaves" the ground circuit.

Structurally, the implementation of this method of protection against electric shock for apartments, office space consists in laying a separate grounding conductor PE (Fig. 6), which is subsequently grounded in one way or another.

How this is done is a topic for a separate conversation, for example, in a private house you can make a ground loop yourself. Exist various options with its advantages and disadvantages, but for further understanding of this material they are not fundamental, since I propose to consider several purely practical issues.

HOW TO DEFINE PHASE AND ZERO

Where is the phase, where is zero - a question that arises when connecting any electrical device.

To begin with, let's look at how to find phase. The easiest way to do this is with an indicator screwdriver (Figure 7).

With a conductive tip of the indicator screwdriver (1) we touch the controlled section of the electrical circuit (during operation, the contact of this part of the screwdriver with the body is unacceptable!), Touch the contact pad 3 with the finger of the hand, the glow of the indicator 2 indicates the presence of a phase.

In addition to the indicator screwdriver, the phase can be checked with a multimeter (tester), although this is more laborious. To do this, the multimeter should be switched to the AC voltage measurement mode with a limit of more than 220 volts. With one probe of the multimeter (which one - it doesn’t matter) we touch the section of the circuit being measured, with the other - natural grounding(heating radiators, metal water pipes). With the readings of the multimeter corresponding to the mains voltage (about 220 V), there is a phase on the measured section of the circuit (diagram Fig. 8).

I draw your attention - if the measurements taken show the absence of a phase, it is impossible to assert that this is zero. An example is in Figure 9.

1. Now there is no phase 1 at the point.
2. When switch S is closed, it appears.

Therefore, you should check all possible options.

I want to note that if there is a ground wire in the electrical wiring, distinguish it from the neutral conductor by the method electrical measurements within the apartment is not possible. As a rule, the wire that is used for grounding has a yellow green color, but it is better to verify this visually, for example, remove the socket cover and see which wire is connected to the ground contacts.

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