What is a RCD?
- Sensitivity – milli Amperes (mA)
- Current Rating – Amperes (A)
- Short Circuit Rating – Kilo Amperes (kA)
- Poles – 2 Pole or 4 Pole
Difference between RCD, RCCB & RCBO
- RCD is the generic term for all types of residual current protective device.
- RCCBs are residual current operated circuit breakers without integral overcurrent protection known in Germany as Fehlerstrom-Schutzschalter (FI-Schutzschalter).
- RCBOs are devices which feature an integrated overcurrent protection unit for overload and short-circuit protection in addition to protection against residual currents.
Operating Principle of a Residual Current Device
The basic operating principle of a residual current device (RCCB, RCBO etc.) is given in the figure below.
|Operating principle of Residual Current Circuit Breaker|
A common cause of unwanted tripping is failure to connect the neutral through the RCD, RCDs work equally well on single phase, three phase or three phase and neutral circuits, but when the neutral is distributed it is essential that it passes through the toroid.
Test Circuit in RCD
A test circuit is always incorporated in the RCD. Typically the operation of the test
button connects a resistive load between the line conductor on the load-side of the RCD and the supply neutral.
The test circuit is designed to pass a current in excess of the tripping current of the RCD to simulate an out-of-balance condition.Operation of the test button verifies that the RCD is operational.It is important to note,therefore,that the test circuit does not check the circuit protective conductor or the condition of the earth electrode.
On all RCDs a label instructs the user to check the function of the RCD at regular intervals and to observe that the RCD trips instantly.
Types of Residual Current Device
It is not designed to give protection against overloads and/or short-circuits and must always be used in conjunction with an overcurrent protective device such as a fuse or circuit-breaker.
In addition it is designed to give protection against overloads and/or short-circuits and can be used independently of any other overcurrent protective device within its rated short-circuit capacity.
Working of a Residual Current Device
|Working of Residual Current Device|