New Mains

What are RCD's and why are they necessary?

I still see many old installations that have consumer units that offer no RCD protection even though they have been required since 2009.

What do RCD's do? They protect against earth faults or leakage. Simply put, they cut out if there is an imbalance on any of the circuits it is protecting. Generally in a home an RCD will be protecting 4 to 6 circuits and there's usually 2 RCD's.

Whereas a circuit breaker (MCB- Miniature Circuit Breaker) will trip if there is a short circuit or overload on a circuit, ensuring that the wires are not getting damaged by overheating or worse, causing a fire-

An RCD (Residual Current Device) is more for the safety of people than the wires. It takes only 30mA of current flowing to earth to make the RCD will trip. Quite sensitive. The reason for making RCD's cut out at this figure is it takes more than 30mA to cause a cardiac arrest should they get an electric shock.

So RCD's are as important as MCB's and although they both work on the same principle of cutting the power to a circuit under fault conditions, they protect against different types of fault.

Also important to note is that RCD's have a test button for you to check regularly every three months.

Stay safe.

Electrician's Log - Skircoat Green, Halifax
9th Nov, 2018

I get a lot of these. It's amazing to me how many houses still have the old rewireable fuses type of consumer unit. If you still have one of those you definitely need to change to a new RCD protected consumer unit. Every new mains (consumer unit) i do means i also inspect, test and certify the entire electrical instllation and certification is NAPIT backed and covers a 10 year period from the date of testing. 5 years if it's a rental property. So here's the end result, neat, tidy and most importantly, safe.