The main purpose of circuit breakers used in household electrical networks is the timely shutdown of consumers in the event of a short circuit or exceeding the rated current as a result of 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) reacts to a sharp increase in current, and the other (thermal) opens the circuit in the event of an unacceptable increase in the temperature of the conductors.
Failure of the protection to fulfill its functions can lead to excessive heating of the network elements, their destruction or a fire. Therefore, when installing or repairing electrical wiring in the apartment it is extremely important to choose and install its protection devices correctly.
It is quite natural that the values of the rated current and voltage, as well as the opening time, are different for various circuit breakers.
In order to understand the criteria and rules that are usually followed when installing these devices, you should take a closer look at their technical characteristics.
Most of these characteristics can be determined simply by looking at the corresponding markings on the circuit breaker body.
Rated current
This characteristic shows what maximum permissible current can flow through this device for a long time without causing the thermal release to trip.
To calculate this value for a separate single-phase line, you need to divide the total power of electrical appliances connected to it by the mains voltage. For example, with a consumer power of 3 kW, the rated current will be:
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 the power factor, which can greatly affect the result if there are large consumers of reactive energy in the electrical circuit. 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 choose a device that has the nearest (larger) to the calculated current rating from the standard range. 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 characteristics of the wiring do not correspond to the power of the consumers connected to it, then it is necessary to conduct a separate line designed to power large loads (washing machine, electric stove, air conditioner, 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 time characteristic
This characteristic shows the dependence of the opening speed of the release contacts on the amount of current flowing through them. The fact is that some devices used in household electrical networks have sufficiently large starting currents, much higher than the rated currents.
In order for the machine not to work at the time of starting such devices, it must be able to withstand these currents for a certain period of time, after which the electrical appliance returns to normal operation and the current in the network decreases to its nominal value. If this does not happen, then an emergency situation takes place, and the electromagnetic release of the machine will disconnect the line.
In household electrical networks, circuit breakers are used that have three types of time-current characteristics:
- B. Designed to power sockets and lighting lines.
- C. The most common type of switches, 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 introductory disconnecting device in the power supply system of an apartment or a private house.
- Circuit breakers 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 by ten times, the machine having the characteristic D will turn off 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 with one or two poles are used. Three-pole devices are used to install a three-phase motor in the power circuit, and four-pole automata are used to protect consumers of a four-wire three-phase network (with a dedicated zero).
If all of the above values are determined, then choosing a circuit breaker for installation in an apartment is not particularly difficult. However, there are a few more important points that you should pay attention to when installing a protection system consisting of several switches.
- To ensure maximum reliability, it is better to use machines from one manufacturer.
- It is necessary to select the current 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 turn off only that section 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 automata.
- To avoid purchasing a device that is of poor quality or does not meet the declared characteristics, it is better not to buy it from unverified suppliers. For this purpose, there are specialized shops or, ideally, certified dealers of reliable manufacturers.
Using such simple rules, you can reliably protect yourself from the occurrence of unpleasant situations associated with accidents or poor performance of the household electrical protection system.
