These are all types of circuit protection.

RCD – Residual Current Device

This is used to monitor the difference between the live and neutral. Should there be a difference above the desired threshold, it is assumed that this leakage is down to a fault and the device will trip out to protect the system and users. This will generally have a test button that should be pressed periodically to ensure it is working correctly.

RCBO – Residual Current Breaker with Overload protection

This device is used to combine an RCD and MCB. This offers protection against leakage between the live and neutral like an RCD, but also protects the cabling and connections against an overload of current like an MCB. This will generally have a test button that should be pressed periodically to ensure it is working correctly.

MCB – Miniature Circuit Breaker

This is used to monitor the current passing through the circuit. Should the demand for power be greater than the designed load on the circuit, due to a fault or too many appliances being connected, this will trip out.

MCCB – Moulded Case Circuit Breaker

This operates in the same way as an MCB, but has the capability for more current to pass through. These are generally for applications above 125A and have a larger air gap when disconnected.

Typically, all final circuits should have RCD protection of 30mA. This can be achieved using a fixed value RCD or RCBO or by using a variable RCD.

Why do I want a variable RCD?

We offer variable RCDs on our Three Phase outputs to allow for Cumulative Leakage while still offering protection against faults. Should a Three Phase appliance be connected to one of these outputs, it becomes a final circuit and the RCD can be set to 30mA. If this output is used to feed another distribution board, the RCD can be set to a higher amount to protect the cabling and the final circuits be set to 30mA further down the line.

What is Cumulative Leakage?

This is a term used where the expected leakage of multiple circuits is added together. In an ideal system there is no leakage however in reality systems often have a small amount of leakage. This low level of leakage on a final circuit may not trip out a 30mA RCD, but if you were to combine the leakage from several final circuits, this may trip out a 30mA RCD. To prevent this nuisance tripping, the RCD can be set to a higher current provided there is 30mA protection further down the line.