Rating of current circuit breakers

The main purpose of the circuit breakers used in domestic electrical networks is timely consumer shutdown in the event of a short circuit or exceeding the rated current value as a result overload.

In order to be able to perform both of these functions, any circuit breaker must be equipped with two types of releases, one of which (electromagnetic) responds to a sharp an increase in current, and another (thermal) opens the circuit in case of an unacceptable increase in temperature conductors.

Failure to protect their functions may lead to excessive heating of network elements, their destruction or fire. Therefore, during installation or repair electrical wiring in the apartment It is extremely important to choose and install devices for its protection.

It is natural that the values ​​of the rated current and voltage, as well as the trip time, are different for different circuit breakers.

In order to understand the criteria and rules that are customary to follow when installing these devices, you should carefully look at their technical characteristics.

Most of these characteristics can be determined simply by looking at the corresponding markings on the circuit breaker case.

Rated current

This characteristic shows what maximum permissible current can flow through this device for a long time without causing the trip of the thermal release.

To calculate this value for a single single-phase line, it is necessary to divide the total power of the connected electrical appliances to the mains voltage. For example, with a consumer power of 3 kW, the rated current will be equal to:

Inom = P / U = 3000/220 = 13.6 A.

It should be noted that the values ​​calculated in this way are not absolutely accurate, since they do not take into account power factor, which can greatly affect the result if there are large consumers in the electrical circuit reactive energy. However, since in most cases such a load is not found among household devices, it is quite acceptable to use this formula to select a circuit breaker. In this case, you need to select a device that has the closest (larger) to the rated current from the standard series. For our case, a 16 A circuit breaker is suitable

An important condition that must be observed when choosing a circuit breaker is the ability of the wiring to withstand its rated current. In order to determine this parameter, you need to know the cross section of the conductor and the material from which it is made. Using these data, you can easily determine the value of the maximum permissible rated current using the appropriate tables.

If the wiring characteristics do not correspond to the power of the consumers connected to it, then it is necessary to carry out a separate line designed to power large loads (washing machine, electric stove, air conditioning and etc.)

Rated voltage

Everything is very simple here, for a single-phase network, you should choose machines with a nominal value of 230 V, and for a three-phase network - 380 V.

Type of current-time characteristic

This characteristic shows the dependence of the trip speed of the trip contacts on the magnitude of the current flowing through them. The fact is that some devices used in household power networks have sufficiently high inrush currents, far exceeding the rated currents.

In order for the machine to not work at the time of starting such devices, it must be able to withstand these currents for a certain the period of time after which the appliance goes to normal operation and the current in the network decreases to its rated values. If this does not happen, then there is an emergency, and the electromagnetic release of the machine will disconnect the line.

In household power networks, circuit breakers are used that have three types of time-current characteristics:

• AT. Designed for power outlets and lighting lines.
• WITH. The most common type of circuit breaker is used to power more powerful consumers than in the previous case (including motors with small starting currents). Such an automatic machine can be used as an input disconnecting device in the power supply system of an apartment or private house.
• Automata with this type of characteristic are mainly used to protect electric motors.

As can be seen from the figure, even if the current in the circuit exceeds its nominal value ten times, an automaton having the characteristic D will disconnect the circuit with a delay of 1 to 2 s.

Rated breaking capacity

This characteristic shows what maximum current value can be turned off by this machine.

Number of poles

In single-phase networks, switches having one or two poles are used. Three-pole devices are used to install a three-phase motor in the power circuit, and four-pole machines are used to protect consumers of a four-wire three-phase network (with a zero).

If all of the above values ​​are determined, then choose a circuit breaker for installation in the apartment is not particularly difficult. However, there are some more important points that you should pay attention to when installing a protection system consisting of several switches.

1. To ensure maximum reliability, it is better to use machines from one manufacturer.
2. It is necessary to select the ratings of the circuit breakers in such a way as to ensure the selectivity of the automatic protection system. That is, in case of emergencies, it should disconnect only that part of the network where such a situation arose. To ensure this parameter, it is necessary to select devices with a large value of the rated current as general automatic machines.
3. To avoid acquiring a low-quality or non-conforming device specifications, it is better not to buy it from unverified suppliers. For this purpose, there are specialized stores or, ideally, certified dealers from reliable manufacturers.

Using these simple rules, you can reliably protect yourself from the occurrence of unpleasant situations associated with accidents or poor-quality operation of the protection system of the household power supply network.