What is a residual current device

Electrical devices surround us everywhere. Sometimes, even when cycling outside the city, we do not forget to put a mobile phone in your pocket, and this is also an electronic device. At the same time, every person from childhood is aware of the danger that electrical appliances contain. However, it is probably not worth to give up the benefits that electric energy brings with it. Especially now, when the requirements of the PUE become more stringent every year, and the industry offers new means of protection. Among them, special attention should be paid to devices of protective switching-off.

Grounding, automatic, RCD ... what's next?

If a couple of decades ago an ordinary electrician were asked to list technical solutions designed to protect a person from electric shock, then surely a protective earth, a fuse and a properly selected circuit breaker would be indicated. Also, the list could complement the transformer isolation of power and management chains. But if in the production of these solutions it is quite natural, then what to do with household electrical circuits in which the ground loop was not envisaged? Machine? But even the most sensitive models (class A) are triggered when the rated current is exceeded by almost five times! With the advent of powerful household appliances, the issue began to demand an immediate solution. And it was found. It turned out to be a protective shutdown device or an RCD. Although everything necessary for its emergence has long been known, it was only recently that ideas were put together and embodied in metal and plastic. Thus, the device of protective switching-off can be called a novelty only with certain reservations.

Remember the laws

As is known from the school course of physics, the current passing through the conductor generates a magnetic field around itself. And the lines of his tension rotate. The direction of the vectors is determined by the motion of charged elementary particles. For those who want to learn more about this, you should read about the application of the rule of a borer (right-hand screw). To understand how the RCDs function, it is sufficient to understand that the field rotates around the current wire.

The next property that should be remembered is the appearance of a current in a closed conductor that intersects the rotating lines of the magnetic field strength.

It is on these two laws that a protective shutdown device is based.

Design and operation principle

Inside the RCD housing is a toroidal high-sensitive current transformer through which conductors are passed. Outside, they are output to the terminal pads.

Let's imagine a single-phase network with two wires - zero and phase. A residual current device is included in their break. As soon as the electric load is switched on after the RCD, the current starts flowing through the conductors, the value of which is determined by the load power. While there is no leakage (there is no ground fault), the currents in the phase conductor and in the zero line coincide (the difference is too small). Consequently, the generated magnetic fields rotate counter-clockwise and are compensated, so their geometric sum is zero. As soon as a leak occurs, a difference appears, and a field is created. Because of it, an induction current arises in the transformer of the RCD. The latter, having its own magnetic field, attracts the latch, which removes the return mechanism from the lock. The chain is torn. Such a solution is called a differential automatic switch.