How the Circuit Breaker is Indicated: Description

ESKD requirements for designation of knife switches

The designation on the circuit breaker is quite clear. It is written in ESKD, and foreign metrics systems are written in accordance with the ISO standard. At the same time, the designation of the switches in both of these systems is almost identical. But, as usual, there are some nuances to which we draw your attention in this article.

Basic concepts of electrical circuits

Before analyzing the mapping of a knife switch or other equipment in the diagram, let's deal with several questions. The first one is the types of electrical circuits, and the second is the basic designations on the diagram, which will allow you to read them.

Types of schemes

First of all, you should know that if you open GOST 2.725-68, which still operates in our country, you simply will not find there such a device as a switch. Moreover, you will encounter such a concept as single-line and multi-line diagrams. Therefore. before we understand what the designation of the knife switch on the diagram, let's deal with the schemes themselves.

Four Line Circuit

• We begin our conversation with a multiline diagram, as the most detailed and correct. As it is known in our country, a three-phase network is used to transmit electrical energy. Therefore, it is most correct in the diagrams to designate each phase with the equipment and devices to which they are connected. This scheme is called a three-line.

Three-line electrical network diagram

• In low-voltage networks, in addition to the three phases, there is almost always an N or PEN conductor. That is, four wires. Accordingly, the scheme becomes four-line.
• In addition, there are low-voltage networks that use five wires. Three of them are phase, one is zero - N and one of protective grounding is PE. To display such a scheme should use a five-line scheme.
• For a single-phase network, according to the standards of ПУЭ, three wires must be used - phase, zero and protective grounding. So, the scheme should be three-line. But often, as in the video, for a single-phase network, a two-line circuit is used when only the phase and zero wires are displayed on the circuit.
• Almost always, a two-line circuit is used to display circuits operating on direct current. After all, for the operation of such a scheme, we need two conductors - “+” and “-”.

The same scheme, but in a single line version

• Of course, such multi-line schemes are much more accurate, but the instruction allows the use of a single-line scheme. What it is? A single-line diagram is a type of mapping of an electrical network in which all three phases, as well as zero and protective grounding conductors, if present, are represented by a single conductor.

Single-line diagram with the image of current transformers - TA in a three-line version

• Such schemes are very convenient when displaying large electrical networks, where there are no differences in the scheme of different phases. And even if there are minor differences, the principle is often used whereby most of the scheme is single-line, and a separate piece, for example, three-line.

Basic designations on the diagram

Any basic electrical circuit - knife switches, or any other equipment, has a number of symbols, the understanding of which will provide an opportunity to read the circuit.

In our article we will look at the main ones. All these rules are spelled out in the rules of electrical installations, and are mandatory for all schemes.

Designation of phase conductors

Let's start with the designation of phase conductors. It must be either letter or color. Phase wires are designated by the symbols A, B, C or yellow, green and red, respectively.

Note! Quite often, the designation of phase conductors can be found as L1, L2, and L3. This designation is not provided for PUE, but is often found in foreign companies. And our domestic experts often adopt this method of designation.

• Zero conductor denoted by - N. Often, instead of the lettering designation, a color notation is used - blue.
• The protective earth conductor is designated - PE . On color schemes, it is indicated in yellow-green. But since the price of color schemes is slightly higher, more often there is only a letter designation of phases and protective conductors.

Designation of zero and protective conductor

Note! Quite often on the schemes you can meet the designation PEN. It tells us that before us is a combined conductor of protective grounding and neutral wire. They are marked in blue with yellow-green stripes on the ends. But on schemes this rule is often ignored.

DC Conductors Designation

As for DC circuits, here everything is somewhat different. The positive and negative veins are designated respectively "+" and "-". A color designation, respectively - red and blue. The zero conductor is designated by M and has to have blue color.

Options for hemming switches

Well, now we are ready to disassemble the switch and the designation on the diagram of this element. For greater clarity, all the options for the notation we have tabulated.

Single Line Circuit Breaker

Even if you draw the scheme with your own hands, you must adhere to certain rules. These standards you can see in our pictures. Before you designation of the knife switch on a single-line diagram, or on multi-line diagrams when installing a knife switch only on one of the phases.

Three-phase switch with single-phase disconnection

In disassembling the switches, we have already noted that in a three-phase version, they can either contain a mounting bar, which ensures the simultaneous closure of all three phases, and not have it. This photo shows a switch with the possibility of phase-down.

Three-phase switch with control of all three phases

If the three-phase switch has this bar, then it must be reflected on the diagram. Therefore, on all three or more linear circuits, this bar is displayed. That is, we have a switch with simultaneous switching of all three phases.

Attention: Here I would like to note that two-phase switches are displayed in a similar way. On which, respectively, two switches connected by a bar are displayed. In order not to litter our table, we will not indicate such a designation of the breaker on the diagram.

Three-way circuit breaker

A separate option is the designation of the so-called throw-over switches. These are knife switches that have three positions - “on” position 1, “on” position 2 and “off”. How such a switch is indicated on the three-line diagram, you can see in the figure below.

Cross over switch on single line diagram

The designation on the switch-over switch types for single-line diagrams is shown in the picture on the left. The only difference is that not all three phases are indicated, but only one conditionally average.

Transition from single-line to three-line diagram

We have already said that in some cases you may encounter the transition of a single-line scheme to a multi-linear one. The designation of the circuit breaker on the electrical circuit is just such an option.

Breaker with closed phase "C" in normal operation

Note! On all the above options with phase-controlled control of the knife switch, it is possible to connect one or several elements, which signals their normally closed position. That is, under normal operating conditions, these knife switches should be turned on, and the elements shown open-ended should be turned off.

Conclusion

A switch on the wiring diagram, and the designation of other elements in the diagram, can have many variations. This is due both to the features of the outline of the scheme, and the tasks facing the designer. But in any case, they meet the standards of ESKD and obey a single rule that you can easily catch from the most common designations given by us.