Residual Current Devices (RCDs): what they are, types, application

Residual Current Devices (RCDs) prevents the generation of leakage currents in the power supply system. These devices and circuit breakers that protect electrical wiring from high overloads and short circuits. RCDs have no such properties. It is only activated when leakage currents are generated. They occur if the insulation of the wiring is broken or if a person touches elements that conduct current, electrical appliances with damage. Residual Current Devices react instantly, shutting down an unsafe area within a fraction of a second. This avoids fire and electrocution.

What are Residual Current Devices (RCDs)

RCDs are based on a built-in differential transformer. It compares the current reading in the conductor under load to the value that is returned to the mains. These figures must match, The total value of the magnetic flux that moves through the magnetic conductor must be zero. If a person touches parts of the device that conduct current, some of the voltage will pass through their body and go into the ground. And because of this, the value of the magnetic flux is no longer zero. Induction then occurs, so the relay trips and the damaged part of the circuit is disconnected.

Types of Residual Current Devices (RCDs)

Many modifications of this device have been developed. RCDs have different technical characteristics. There are main types of RCDs. One of the main differences is in their details. RCDs come in two types of construction:

• The more reliable and electromechanical models, as they work steadily.
• Electronic RCDs have an amplifier that must receive power. If the zero is damaged and there is no power to the amplifier, the device does not respond to the leak.

Types of RCDs by type of current leakage:

• Type AC is a device for sinusoidal alternating current.
• Type A is suitable for pulsating direct current.
• Type B is designed for direct current.

The short-circuit current limit value differs. The most popular values are 4.5 kA, 6 kA or 10 kA. The speed of operation of RCDs also differs: type G gives a normal response without delay. Type C is a selective RCDs, which has a time delay ranging from 150 to 500 ms.

Application of RCDs

RCDs are installed in new buildings in residential neighborhoods, in office and public buildings, and in the workshops of industrial plants as a matter of course in many countries. They are also required in rooms where power tools are used under particularly dangerous conditions. RCDs are included in the completion of distribution boards, electrical panels in apartments and on the floors. Commercial containers made of metal, modular buildings are also necessarily equipped with RCDs. This system requires proper earthing in accordance with the modern rules of the energy sector. This applies to both organizations and private users of electricity.