Protection against leakage currents: RCD and difavtomat

Why do I need an RCD and a difavtomat? What is the general principle of their work? What is the difference?

According to the current rules for the installation of electrical installations, the wiring of rooms with increased danger must be equipped with protection against leakage currents. See what is leakage current here - Leakage current in electrical networks, how to check and find leakage current.

In a residential apartment, a room with increased danger is considered to be a bathroom. Often, such a room is considered a kitchen. Both there and there may be a higher air temperature, tightness of space and high relative humidity. These factors lead to the fact that the insulation of wires and electrical equipment wears out faster, and the contact voltage increases to deadly values.

To eliminate this danger, protection against leakage currents is established, which is usually implemented on the basis of residual current device (RCD) or differential automaton. Both of these devices “compare” the electric current flowing through the phase wire with the current in the neutral conductor. When a difference occurs, the unit breaks the circuit.

This means that both the RCD and the difavtomat do not allow electric current to flow “to the side”, that is, to the ground. It turns out that even if a person gets under voltage by touching the phase wire directly or through the housing of the appliance with damaged insulation, the protection devices against leakage currents can save him from certain death. After all, they are triggered by a difference of currents from 10 mA in a time calculated in fractions of a second.

The choice of apparatus for protection against leakage currents must be approached correctly. If you install a 100 mA difavtomat in the bathroom power line, then such protection can hardly be considered effective. A person can very seriously suffer from electric shock, but for a machine it will be a normal mode, the circuit will not open. Therefore, it is better to provide an RCD or a difavtomat for 10-30 mA to the bathroom or kitchen. If desired, you can put an apparatus operating at the above 100 mA on the general input of the apartment. This will ensure the selectivity of protection, that is, the line in which there is a malfunction will be disconnected.

UZO and difavtomaty are not a panacea and salvation from all the dangers associated with the use of electricity. They won’t save if you decide to touch the phase and zero working conductors at the same time, because the device cannot distinguish whether the current goes through the load or the human body. This must always be remembered, to protect live parts that are normally energized from direct contact and do not forget to disconnect the line from voltage during repair.

Finally, we’ll talk about What is the difference between UZO and difavtomat. Everything is relatively simple: RCD provides protection only against leakage currents. It does not provide maximum current protection, therefore, if, for example, a piece of wire is inserted into the socket of a network protected only by an RCD, with two ends, then the unfortunate RCD will burn along with the wiring, but it will not disconnect anything. Indeed, the current difference in the phase and neutral conductor in this case will be absent. And if you chose RCD as a protection against leakage currents, then you must also include a conventional circuit breaker with the appropriate setting in the circuit.

And if you have a desire to save space in the apartment switchboard, it is better to give preference differential circuit breakerwhich alone provides both overcurrent protection and protection against leakage currents.

See also: Schemes for connecting RCDs and differential machines

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