Choice of current circuit breaker

When assembling an electrical panel or when connecting powerful household appliances to a home network that creates an additional load, the master is faced with the task of choosing the right protective automatic devices. These devices provide protection for the circuit and all the elements included in it, so it is important not to make the wrong choice. How to choose the right ratings for current circuit breakers? This will be discussed in the presented material.

Circuit breaker assignment

Before we deal with the question of how to choose a circuit breaker, let's decide what this device is for. Installing the machine in an electrical circuit prevents overheating of the wiring and its failure. Any cables are designed for a certain amount of current, the excess of which leads to the fact that the temperature of the wire increases significantly. If this is not prevented in a timely manner, the conductor will soon begin to melt. The result, as a rule, is a short circuit (SC), which can not only damage the electrical wiring and household appliances connected to it, but also cause a fire.

To prevent this, a circuit breaker (AB) is installed, which, in the event of a dangerous situation, will de-energize the network.

Another function of the circuit breaker is to turn off the power when a short circuit has already occurred for some reason.

The short-circuit current can exceed the rated one by hundreds of times. Neither wires nor household appliances can withstand such a load, and it is very important to turn off the power in time as soon as the current exceeds the permissible limit.

To reliably protect the home network, it is necessary to correctly select the ratings of the circuit breakers installed in an apartment or in a private house.

Clearly about the circuit breakers in the video:

Varieties of protective devices

There are several types of AV, which are connected to the network in order to monitor the condition of the wiring and, if necessary, to interrupt the supply of current. They can be as follows:

• Mini models (small dimensions).
• Air (open type).
• Residual current devices (abbreviated name - RCD).
• Closed (device elements are located in a molded case).
• Differential (automatic switches combined with RCDs).

Mini Models

These machines are designed to operate in low-load circuits. They usually do not have the function of additional adjustment. In this series are devices that can withstand a misfire current of 4.5 - 15A. They are not suitable for factory capacities, since the current strength in enterprises is much higher than their rating. Therefore, they are usually connected to household wiring.

The machines included in the production line of the French company Schneider Electric are very popular. The ratings of AB, produced by this company, can be 2 - 125A, so you can choose a bag for home lines of various powers.

Air (open) devices

If the total power of the devices connected to the network is large, and the ratings of the machines mentioned above are insufficient, air protective devices should be chosen. The rated cut-off current of open-type bags is an order of magnitude higher than that of mini-models. Most often they are three-pole, but recently many companies have established the production of four-pole machines.

Open-type protective devices should be installed in distribution cabinets equipped with special DIN rails from the inside.

If the protection class of the cabinet is from IP55, then it can be placed outside the building. The body of this equipment is made of refractory metal and is reliably protected from moisture penetration, which ensures a high level of security for the machines located inside it.

Air ABs have a big advantage over miniature ones. It consists in the possibility of adjusting their nominal characteristics using special inserts that are placed on the active contact.

The machines belonging to this model range differ from each other only in width, which depends on the number of poles in the device (two or more). For the rest of the dimensions, they completely coincide.

Closed circuit breakers

The body of these devices is molded from refractory metal, which ensures perfect sealing and makes them suitable for use in harsh conditions. The maximum voltage indicator that such machines can withstand is 750V, and the current is 200A. Closed AVs are classified according to the type of action into the following groups:

• Adjustable.
• Thermal.
• Electromagnetic.

The optimal type should be chosen based on the tasks to be solved.

The highest accuracy is possessed by closed electromagnetic automata, which determine with a minimum error the root-mean-square indicator of active electric current and instantly de-energize the network in the event of a short circuit, avoiding serious consequences.

Electromagnetic machines are successfully used to control the functioning of the motors of factory machine tools, as well as other powerful equipment, since they can withstand amperage up to 70 kA. The figure denoting the current rating of the machine is printed on its body.

All types of enclosed circuit breakers can have two to four poles. Due to this, they can be used to protect electrical networks of any buildings and structures of residential and non-residential type.

Residual current devices

Residual current devices should not be used as independent protective devices, since their main task is to protect a person from sudden electric shock. Therefore, it is recommended to install them together with AB, or to purchase a differential machine, which already contains an RCD. In the first case, you need to take into account that, first of all, a residual current device should be installed, and after it automatic machines.

If you change the installation order, then a short circuit will lead to the failure of the RCD due to too high a load.

How to choose a wire?

It is not uncommon that a new circuit breaker and meter are connected to the wiring of an old house, an RCD is installed, but the cable itself is not changed. In this case, the choice of the automatic machine for current is made correctly, taking into account the total power of the household appliances installed in the house. But after a while, the insulation begins to smoke and melt, and the protective device does not react to this.

The reason is that, although the choice of the circuit breaker and related devices was made correctly, the wiring is not able to withstand such a load.

Therefore, when connecting additional household appliances, you must make sure that the wiring in its cross section is suitable for such capacities.

Below is a table, according to which you can find out what the wire cross-section should be at various loads.

Calculation of rated current

The choice of the circuit breaker is made taking into account the total power of the electrical appliances included in the circuit (P) and the mains voltage (U), according to the formula I = P / U... This takes into account all the elements included in the power grid (lighting devices, household appliances, electric heaters).For convenience and clarity, we will give one more plate, having consulted with which, you can easily determine how many Amperes to put the machine in this or that case. It contains parameters for both single-phase and three-phase connections.

For powerful electrical installations with a reactive load (these include transformers, electric motors), the selection of circuit breakers is not done in terms of power. The rating of the protective device in this case is selected based on the value of the operating, as well as the starting current. These data are given in the technical data sheet of the device.

An example of calculating the rated current for a circuit breaker in the following video:

Conclusion

In this article, we talked about what the electrical network protection devices are for, what types of these devices are, and also figured out how to correctly select the ratings of the current protection circuit breakers. This information will be useful to you if there is a need to select machines for your apartment or private house.