Wire color coding. Brown and blue wire - which one is plus, which is minus

Today, the installation of electrical wiring is unthinkable without the use of conductors in colored insulation. Color marking is not a tribute to fashion and not a marketing ploy of a manufacturer who, as it may seem to someone, wants to present their products in a colorful way.

In fact, this is an urgent need. Firstly, color coding allows you to specify the purpose of each conductor in a particular group to facilitate their switching. Secondly, the probability of an error during wiring and, as a result, the occurrence of a short circuit during a trial run or a defeat is significantly reduced. electric shock in the process of network maintenance and repair.

Certain colors are not chosen randomly. All the variety of colors is reduced to a single standard - PUE. They indicate that the cores of the wires should be identified by color or alphanumeric designations.

As part of this publication, the color marking of wires will be considered. With the adoption of a single standard for the color identification of electrical conductors, the work of switching them has been greatly facilitated. Each vein that has a specific purpose is designated by a unique color: brown, gray, yellow, green, blue, etc.

Color marking is usually carried out along the entire length of the conductor. Identification is also allowed at the ends of the cores and at the connection points, for which colored heat shrink tubing(cambric) or colored electrical tape.

Consider how it is performed in a three-phase, single-phase and direct current.

Color of wires and tires at alternating three-phase current

In three-phase networks, busbars and high-voltage inputs of transformers on power stations and substations, painting is carried out as follows: yellow colored wires and busbars with the "A" phase, green with the "B" phase, and red with the "C" phase.

DC network - what color are the plus and minus wires

Beyond networks alternating current in national economy DC circuits are used, which are used in the following areas:

• in industry, construction, storage of materials (loading equipment, electric carts, electric cranes);
• in electrified transport (trams, trolleybuses, electric locomotives, motor ships, mining dump trucks);
• at electrical substations (for powering automation and operational protection circuits).

The DC network uses only two wires. In such networks, there is no phase or neutral conductor, but there is only a positive bus (+) and a negative bus (-).

By regulation, wires and rails of positive charge (+) must be colored red, and wires and rails of negative charge (-) must be blue. The middle conductor (M) is indicated in blue.

If a two-wire DC electrical network is created by branching off a three-wire DC circuit, then the positive conductor of the two-wire network is indicated by the same color as the positive conductor of the three-wire circuit with which it is connected.

Colors of wires phase zero earth in wiring

For gasket electrical networks AC apply stranded wires in multi-colored insulation, which greatly simplifies installation work and eliminate confusion.

Designation of wires by color this is especially true when the wiring is done by one person, and the subsequent maintenance or repair will be handled by another. Otherwise, the latter will have to constantly look for either “phase” or “zero” with the help of a probe.

Those who have worked with old wiring know how annoying it is sometimes. After all, earlier the insulation of the electrical cable used in everyday life was one-color - white or black.

Since the days of the USSR, the color marking of electrical wiring has undergone a number of changes until a certain standard has been developed. Now each color of the current-carrying conductor determines its purpose in the cable.

Nowadays, the regulatory document governing the color marking of insulated or non-insulated conductors is PUE 7, where, in accordance with GOST R 50462 "Identification of conductors by colors or numerical designations", only certain colors and designations.

Main task wiring markings is the speed and ease of determining the purpose of the conductors along the entire length, which is one of the main requirements of the PUE.

Consider what color conductors should have today in AC electrical installations with voltages up to 1000V and with a solidly grounded neutral (this category includes most administrative buildings and residential buildings).

Color of zero protective and zero working conductors

Blue color indicates zero working conductors (N). Zero protective (PE) conductor must be painted in yellow-green longitudinal or transverse stripes. This combination of colors should only be used for marking pinching conductors (zero protective).

Combined zero working and zero protective (PEN) - blue color along the entire length of the conductor with yellow-green stripes at the ends (at the junctions). It is characteristic that GOST today also allows the opposite color option - yellow-green stripes along the entire length with blue at the ends (at the junctions).

Simply put, designation of neutral wires by color should be:

1. 1) zero working (N) - blue color;
2. 2) zero protective (PE) - yellow-green color;
3. 3) combined (PEN) - yellow-green blue marks at the ends.

Phase wire colors

In accordance with the PUE, when designating phase conductors, preference is given to one of the following colors: black, brown, red, gray, purple, pink, white, orange, turquoise.

A single-phase electrical circuit can be created by branching from three-phase network. In this case, the phase wire single-phase circuit the color must match the phase conductor of the three-phase network with which it is connected.

Wire color coding must be carried out in such a way that the color of the phase conductor does not match the color of the N-, PE- or PEN-conductor. When using an unmarked cable, colored marks are placed at its end (at the junction). In this case, a colored heat shrink tube (cambric) or colored electrical tape is used for designation.

To save yourself from unnecessary work in the form of leaving marks with electrical tape or tubes, it is enough to correctly determine the color marking of the insulation before buying an electrical cable. You should also buy it from the right amount to ensure the same wiring markings throughout the apartment or throughout the house.

If the cable is already laid how to mark

Very often you have to deal with such situations when you come to the object, open the shield, and there the connection is not clear how. There is no need to talk about the correspondence of wire marking with the rules. It is not clear where the phase is, and where is zero and ground. You have to familiarize yourself with the wiring in the shield, junction boxes etc. It all comes down to one drawback, you have to waste time. How to be in that case? Do not reconnect.

Currently, the industry produces electrical wires different section with alphanumeric and color-coded cores along the entire length of the wire. Main function any type of marking - visual recognition of each individual wire core for its intended purpose, as well as facilitating (accelerating) the installation and operation of wires.

In addition, the separation of cores by color in the power electrical circuit is also one of the modern safety requirements regulated by GOST.

electrical wire It is widely used in production and in everyday life both in AC power circuits (single-phase 220V network or three-phase 380V network) and in DC circuits. Electric wire is single-core and multi-core. The cores of the wire can be single-wire or multi-wire.

Single-phase two-wire network 220V

A two-wire electrical network is an electrical network with two electrical conductors. One conductor is phase, the second is zero. The two-wire electrical network is still found today in older homes in the form of conventional electrical wiring. Old electrical wiring is a two-wire aluminum wire("noodles") with white insulation.

A two-wire wire is used to connect switches, conventional sockets, lamps.

Because since both cores of such a wire have the same color, it is rather problematic to visually distinguish the phase from zero. Therefore, in order to determine where the phase is and where it is zero, they use an indicator screwdriver, a probe, a “continuity”, a tester, a multimeter or other electrical measuring device.

Today, in order to distinguish the phase from zero during operation, either a two-core wire with wires of different colors or two single-core wires is used during installation.

As a two-core wire, a flexible wire with a brown and blue (light blue, blue) core is often used. It is strongly recommended to use a brown conductor as a phase conductor, and a blue conductor as a neutral conductor.

Often there are two-core wires with a different color of the cores. For example, in such wires, the phase wire may not be brown, but red, black, gray or another color.

In the case of using two separate solid wires, there are two marking options. The first is the use of wires of different colors. For example, you can use a red wire as a phase, and as a zero blue wire.

If wires of the same color are used, then the phase and neutral cores can be marked either with colored electrical tape or by using colored heat shrink tubing. When using colored electrical tape, red electrical tape is wound on the phase wire at the beginning and at the end, and blue electrical tape is wound on the neutral wire.

When using heat shrink, marking single-color wires is almost the same as marking with electrical tape. Red heat shrink is put on the phase wire, and blue heat shrink is put on the neutral wire.

At home, you can mark wire cores with other colors.

Color marking in a single-phase three-wire network 220V

A three-wire electrical network is a network with three electrical conductors. Currently, a three-wire network is becoming more and more common, especially for new wiring.

As in a two-wire network, one conductor is phase, the second is zero, but the third conductor is a protective ground wire that serves to protect against electric shock. In a three-wire network, a three-wire wire is used, usually with a brown, blue and yellow-green core.

The brown wire is a phase, the blue wire is a neutral conductor, the yellow-green wire is a protective earth conductor. To avoid confusion, it is not recommended to use a core with a yellow-green color as a phase or neutral conductor.

A three-core wire with colored wires is used to connect modern European-style sockets that, in addition to phase and zero contacts, also have a contact for connecting a ground conductor. Three-wire wires are also used to connect fixtures.

Color designations of wires in a three-phase network 380V

A three-phase electrical network can be four-wire or five-wire, i.e. with four or five wire cores. The only difference is the presence or absence of a protective earth conductor. Those. a four-wire network is three phase conductors, a zero working conductor and the absence of a protective earth conductor. A five-wire network consists of three phase conductors, a zero working conductor and the presence of a ground conductor.

In both the four-wire and five-wire networks, a blue wire is used for the zero working conductor, and a yellow-green wire is used for the ground conductor. As for the three phases A, B and C, the brown, black and gray cores are most often used for them, respectively. But there are also other colors of wire cores.

A four-core and five-core wire is used to connect a three-phase load or to separate a single-phase load into groups.

DC network

In a DC electrical network, two conductors are usually used. The first conductor is the plus and the second conductor is the minus. The red conductor is used as the positive conductor, and the blue conductor is used as the negative conductor.

As a result of all of the above, it is worth noting the following: despite certain standard requirements according to the color marking of wires, it is not recommended to rely on the color of one or another wire core without a preliminary check.

Switching wiring in a private house must be carried out by color. The best answer on how wires are marked by color is given by GOST R 50462. But unfortunately, practice shows that electrical lines in the private sector, it is not uncommon that they perform not with the material they should, but with what they have. This article does not cover other technical aspects wiring devices. The following information gives an idea of ​​how the conductors should be color-coded correctly and how to remedy the situation in the event of a discrepancy.

The conductors may be colored in their entirety or marked with a thin strip of color along the length of the conductor's insulation. We also produce cable products that have a two-color color.

The color of the phase and neutral wires in the input cable

The supply lines leading to the house can be made in several versions. It all depends on the type of cable. If single-phase input is performed:

1. With a SIP type wire, the phase conductor will have a colored stripe (usually yellow, green or red). Zero core black.
2. Cable type AVVG or VVG, then the neutral conductor is blue, white, red or green - phase.
3. Cable type KG - phase wire brown, zero - blue.

If a three-phase input is performed:

1. A SIP-type wire and in addition to the two primary colors of red and green, blue and black wires - the neutral wire will necessarily be black.
2. With an AVVG or VVG type cable, the neutral conductor will be blue, and one of the phase conductors, in addition to red and green, will be black or white.
3. Cable type KG zero - blue, brown and two black - phase conductors.

Cable products are often produced not according to GOST, but according to specifications. Therefore, even in a two-core SIP with black and blue, the black wire will be zero. The black wire contains a steel core, which performs the self-supporting function of the wire. Connecting the input to the house from overhead lines with a VVG and KG type cable is not recommended.

Wiring inside the house is carried out only with single-phase lines and copper wires.

In electrical circuits used for domestic purposes, the working zero must always be blue!

According to the PUE, house lines must be laid with a grounding conductor. In all three-core conductors made in accordance with GOST, suitable for internal works, ground wire - yellow green.

If the three-core conductor is flexible type PVS, then the phase conductor is usually brown. For inside house wiring, it is better to use wires made of cast copper. If the conductors are marked with stripes, then a conductor with a stripe of any color except blue and yellow-green is phase. If there is no yellow-green conductor in the cable, use the conductor with a green stripe as the ground wire. The ground wire may be marked in pure yellow. In cables, the cores of which are colored entirely, the white wire is the phase wire.

Connection to the electric stove

A 220v household electric stove is connected to a special outlet that can withstand high power. The color of the cores is red, green, blue, where red is the phase, green is the earth, blue is the neutral conductor. There is a nuance in electric stoves and hobs, foreign-made, designed for 220/380V, the connection is made with a four-wire conductor:

• blue - zero;
• yellow-green conductor - grounding;
• black conductor - phase A;
• brown conductor - phase B.

It is allowed, when connecting to a single phase network, to combine phase conductors on an electric stove under one contact clamp.

Neutral wire

Neutral conductor is a wire connected to the middle (zero) point electrical system. IN standard scheme connection is a combined zero working and zero protective conductor in a three-phase circuit. The color of the neutral wire is all blue with yellow-green ends or all yellow-green with blue ends.

Designation of wires phase, zero, earth

Wires are marked by color, letters and numbers. Until 2009, GOST interpreted the possibilities of marking wires more widely. Starting in 2009, the standards are being revised towards a clearer classification of colors and the elimination of notes that allow conductors not to be marked. IN national standard 2009 clarified terminology and supplemented alphanumeric classification. For electrical circuits until 2009, the classic color of conductors was used: yellow, green, red.

In the classic version of three-phase circuits up to 1000 volts, conductors are marked in the following combinations:

1. Phase A - L1, yellow - brown recommended.
2. Black is recommended in phase B - L2, green.
3. Phase C - L3, red - gray recommended.
4. Zero conductor - N blue.
5. Combined working zero with a grounding conductor - PEN, blue with yellow-green tips - yellow-green with blue tips.
6. Grounding conductor - PE, green-yellow.

This combination does not imply any direction of rotation or phasing.

What color is the phase and zero

In single-phase lines without a ground conductor, the phase conductor is marked in red, the zero conductor is marked in blue. Also often there is a combination of phase - white color, neutral wire - blue color. The worst combination of wire colors, phase, zero, earth found in the coloring of conductors is white, red, black.

If we take identification standards, the phase wire should be red, black - ground conductor, white - zero. But from practice it is better to make zero red, and the phase white. Visually, zero conductors will be better visible. There is a danger of mixing phase and neutral conductors made different materials! It is better to mark the ends of the conductors with insulating tape in standard colors.

Color-coded wire marking for DC lines

DC circuit conductors are recommended to be painted as follows:

• positive pole - red (recommended Brown color isolation);
• minus pole - blue (grey is recommended);
• ground conductor in a three-wire DC circuit - blue (since 2009, blue is recommended).

The polarity of the wires by color can be determined more easily. Cold colors - negative terminal, warm colors- plus. If there are taps in a three-wire DC electrical circuit, then the outgoing lines must be the same color as the supply lines. What color the plus and minus wires were not painted, it is necessary to mark them with an alphanumeric marker.

Electrical wire colors

Even GOST is not mandatory. Conductors can be colored black, blue, green, yellow, brown, red, orange, purple, grey, white, pink, turquoise colors. Prohibitions on the use of yellow and green are clearly given.

The cable cannot contain a core marked with a double color, in combination with yellow or green with anything else, except for just one yellow-green conductor.

To avoid confusion, it is better to put heat shrink tubing on the ends of the conductor. classic colors. Enough 10 cm tube desired color. The opinion in this article is subjective and contains only a recommendation, based on the assumption that all other rules for the installation of electrical installations will be observed.

Video about marking wires and cable lines

Hello, dear readers and guests of the Electrician's Notes website.

When conducting electrical work, very often the question of the color marking of wires is raised.

It used to be, so to speak, in "stagnant" time, only white wires were used, less often black.

Therefore, define in electrical assembly phase or zero, took quite a long time. I had to resort to help and.

To avoid this, it is necessary to bring the color marking of wires and tires to a single standard.

And as always, let's turn to regulatory documents, namely, Chapter 1, clause 1.1.29. and clause 1.1.30. It clearly states that the identification of conductors of wires and tires by colors or digital designations must be used, in accordance with GOST R 50462-92.

And what does this GOST say ?!

According to GOST R 50462-92, clause 3.1.1, the following colors can be used to identify conductors and tires: black, brown, red, orange, yellow, green, blue, blue, gray, white, pink, turquoise.

According to the EIC, clause 1.1.29:

• neutral conductors (N) must be blue
• the combined zero working and zero protective conductors (PEN) must have a blue color along the entire length and yellow-green stripes at the ends
• protective neutral conductors (PE) and protective earth conductors must be green-yellow

Let me give you a few photos as an example. All zero working conductors (N) are connected to the bus (N) and are blue. All neutral protective conductors (PE) are connected to the busbar (PE) and are green-yellow.

And all other colors, except for blue (blue) and yellow-green, can be used as phase conductors.

The photographs below show that the phase conductors are white.

According to the PUE, clause 1.1.30, with an alternating three-phase current, phase A busbars must have yellow, phase B - green, phase C - red. It is remembered easily and simply in the form of the abbreviation "ZhZK", i.e. yellow, green, red.

For clarity, I will give a few examples.

Two measuring transformers NOM-10 (kV).

outgoing feeder distribution substation voltage 500 (V).

As you can see, in the examples given, the color marking of tires with three-phase alternating current is fully respected.

By the way, it is not necessary that the tires be completely painted in one color or another. It is quite enough to make color marking (in the form of paint, stickers, heat shrink tubes, tags, etc.) in the places where the busbars are connected to the switching devices.

According to the PUE, clause 1.1.30, with single-phase alternating current, the phase B bus connected to the end of the power source winding should be red, and the phase A bus connected to the beginning of the power source winding should be yellow.

Unfortunately, I have no good examples of such electrical installations. Maybe someone has photos, I will be very grateful if you share.

By the way, if single-phase current buses are a branch from a three-phase current system, then they are designated according to the color marking requirements of a three-phase system.

According to the PUE, p.

As an example, I will give a direct current shield (SCPT) \u003d 220 (V).

And these are the conclusions directly from the battery.

By the way, we are gradually switching from lead-acid batteries SK-5 to maintenance-free Varta batteries.

Addition

Since 01/01/2011, the GOST R 50462-92 specified at the beginning of the article has been canceled. Instead, GOST R 50462-2009 came into force, in which some points contradict the previous GOST. For example, paragraph 5.2.3 states that the following colors are preferred for phase conductors:

• Gray
• Brown
• the black

I'm posting a photo to illustrate. switchboard one of the banks where we did the wiring.

In my opinion, the previously adopted marking "ZhZK" is more descriptive.

In a single-phase network for a phase conductor, the preferred color is brown. Accordingly, if a single-phase network is a branch from a three-phase network, then the color of the phase conductor must match the color of the phase conductor of the three-phase network.

There was also a ban on yellow and green colors applied separately (clause 5.2.1). They must only be used in the yellow/green color combination for PE protective conductors. In this regard, the marking of the three-phase network "ZhZK" was changed, because. yellow and green colors were used in it separately.

The digital marking of DC circuits has also been changed (clause 5.2.4):

• brown color - positive pole (+)
• gray color - negative pole (-)
• blue color - middle conductor (M)

Attention!!! I want to warn you that you do not need to run now and change the existing markings. After all, when objects were introduced, it was still acting old GOST R 50462-92. But when commissioning new electrical installations, GOST 50462-2009 should not be neglected.

If for some reason it is not possible to mark wires and tires according to the above requirements, then any color can be used. But it is necessary to wind electrical tape, stickers on the ends of the wires, put on cambric or heat-shrink tubes of the corresponding color, for example, like this:

And already by tradition, watch the video based on the materials of this article:

P.S. Dear colleagues, I ask you to comply with the requirements for color marking of wires and tires when performing electrical installation work. Let's respect each other.

important for faster and 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 indicate:

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

It is allowed to use for grounding conductors with green insulation with a yellow stripe, 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 isolation without differences in shades indicates high culture installation 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 inclined stripes of yellow and green color - 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 “GZK” for the paint of 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, the GOST standards stipulate, therefore, when looking at the installation of the power plant, the question should not arise whether the blue wire is a phase or zero, since the blue color and its shades (blue) are taken to indicate neutral ().

Other neutral core colors are not permitted.

The only acceptable use of blue and blue insulation is the designation of the negative pole or midpoint in DC circuits. 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 of bare metal without insulation as a protective ground.

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

Coloring in the network 220V and 380V

Installation of one- and three-phase electrical networks is facilitated if the wiring is made with multi-colored wire. Previously, flat two-core white wire was used for single-phase apartment wiring. 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;
• gray (white) - 3 phase;
• blue (cyan) - working zero (neutral)
• yellow-green - grounding.

Domestic cable products comply with the core color standard, so a multi-phase cable contains multi-colored cores, where the phase is white, red and black, zero is blue, and the ground is yellow-green conductors.

When servicing networks mounted according to modern standards, you can accurately determine the purpose of the wires in junction boxes. If there is a bundle of multi-colored wires, the brown one will necessarily be phase. The neutral wire in the distribution boxes 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, isolation blue tint used when marking the midpoint (zero) of power.

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 decoding the device manufacturer, which is often given in the documentation or on one of the walls of the structure. Example: computer power supply or car 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 - middle point in DC circuits with bipolar power supply.

To designate the protective earth connection terminals, a special symbol is used, which is stamped on the terminal or on the instrument case 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 denoted by the symbols A, B and C.

A deviation from the standards is the combined phase designation system:

• 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 pieces of PVC insulation or a heat-shrinkable tube.

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.