What is an RCD and what does it do?

An RCD is a protective device that goes inside your switchboard. It looks like a circuit breaker, although a little bigger. RCD stands for ‘Residual Current Device’. Its job is to raise the safety bar electrically. There is a significant increase in safety when using RCD’s as opposed to just circuit breakers, and even bigger one when compared to the old porcelain re-wireable fuses. The difference could be related to using arm bands in the water to keep afloat next to a full blown rescue craft with two 200 horse power engines on the back.  As electricity can’t be seen, nor can the dangers so obviously knowing your protected as much as you can be gives you peace of mind for you and your family. 

RCD’s monitor the current flowing through the conductors. Any loss of current in those conductors flowing to earth is detected by the RCD. This essentially trips the RCD and disconnects the circuit. This disconnection happens in milli seconds which ultimately protects equipment but most importantly the human operating the electrical device. 

It’s important to know that  RCD’s are not circuit breakers, and are not designed to trip on overload. They are there to monitor the current flowing in the circuit and are before the circuit breaker. In NZ and Australia each RCD controls 3 circuit breakers. 

There are several different types of RCD’s though. The common every day RCD is as I have explained above, but there is also an RCBO, a RCCB and in some electric vehicle chargers there are RDCDD’s.

The RCBO has the same characteristics as an RCD but the ‘O’  stands for overload, which essentially operates with over load current as well.  

Th RCCB stands for Residual Current Circuit Breaker.  As one would expect this is an RCD with Circuit breaker characteristics as well. 

The RDCDD stands for Residual Direct Current Detecting Device. This is an RCD that detects direct current (DC current) flowing back from the electric vehicle which is DC, into the AC (Alternating Current) system. i.e. Your domestic switchboard.   


So as you can see there is a lot more to RCD’s than most people actually realise. 

If you are unsure if you have RCD’s please reach out to us and we can provide a no obligation free quote to upgrade your switchboard. We are at www.aucklandswitchboards.nzor just email nigel@aucklandswitchboards.nz

We look forward to hearing from you.