What Is a Residual Current Device?
A residual current device, also known as a Residual Current Circuit Breaker,is a switch that opens the circuit of the fuse group it is connected to when the difference between phase and neutral caused by insulation faults exceeds the rated value of the device.
Electrical leakage can occur when any part of the body or another conductive object touches exposed parts of cables and devices whose insulation has worn out or been damaged.
How a Residual Current Device Works
A residual current device is a switch that works on the principle that the currents entering and leaving an electrical circuit are equal. If they are equal, no magnetic flux is created and the circuit keeps working. If there is any leakage, the incoming and outgoing currents will not be equal, the toroid inside the device will be affected and the device will trip within a very short time.
How to Choose a Residual Current Device
30 mA is chosen for protecting life (personal protection) and 300 mA for protecting the installation (fire protection).
The rated current must not be lower than the current that will flow through the device. For example, a 25 A device should be installed in front of a motor drawing 20 A.
Residual Current (Milliamperes) | Tripping Time (Milliseconds) |
>30mA | Does Not Trip |
30mA | 300ms |
60mA | 150ms |
150mA | 40m |
Where Is It Used?
Every electrical device in all our living and working spaces should be supplied through a residual current device. At high current values, the human body can be seriously injured or the heart can stop completely.
How Is It Tested?
Testing the device is very simple. The T button on it is there to check whether the device works properly. If the switch does not open when you press the test button, the device may be faulty or there may be a wiring error in the circuit.
Is a residual current device mandatory?
It is now required by electricity distribution companies, and the related regulations have been amended accordingly.
- Occupational Health and Safety Law No. 6331 – Article 318
- Regulation on Internal Electrical Installations – Article 18
- Regulation on Earthing in Electrical Installations
If there is no residual current device in the fuse box or switchboard in your home, ask a licensed electrician to install one.