10 June 2013

RCDs explained in plain English


SIMPLY PUT, the RCD is the most important safety device in your Consumer Unit. It prevents serious electrocution and can save lives. It can also provide some protection against electrical fires. Don't ignore the importance of this little baby!

In Spain an RCD is called an Interruptor Diferencial (ID) and is easily identified as the device with a test button marked “T” or “Test”. Back in 1992 in the UK, the 16th edition of the IEE Electrical Regulations changed the name of the long standing Earth Leakage Circuit Breaker (ELCB) to the Residual Current Device (RCD) in an attempt to more suitably describe its function.

The RCD protects all the wiring and connected electrical appliances in a Spanish home. It safe guards against leaking electricity by automatically disconnecting the electricity supply in the event of a fault. The RCD must have a minimum rating of 30 mAmps (that's a very small leakage current), which is marked on the device. In the event of earth leakage rising above 30 mAmps anywhere in the installation, the RCD trips-out and will not allow you to switch it back on until the fault is cleared or isolated. This can be inconvenient and a cause of major irritation but may just have saved a life.

A typical Spanish Consumer Unit with 4 sub-circuits, RCD & mains isolater

An RCD differs from a Circuit Breaker in that it is not a fuse. A Circuit Breaker or fuse protects against overloading and short circuit protection, whilst an RCD protects against earth leakage. To have one device that protects against all three faults is very expensive, so it’s more practical to have separate devices.

RCDs are very sensitive and they sit nice ´n quiet in your Consumer Unit (that's a Fusebox in old money) and constantly monitor your electricity supply. When it detects a leak of electricity, normally caused by damp or water ingress, running down an unintended path it disconnects the electricity supply very quickly, significantly reducing the risk of death or serious injury. It prevents conductive fixtures in the home, e.g. metal appliances, stainless steel draining boards, shower heads, copper pipework, etc. from becoming live.

Property owners should regularly test the RCD (or RCDs) every 3 months. If your RCD does not switch off the electricity supply when the test button is pressed, or if it does not reset, contact Sparks.

Every 10 years an electrician should be employed to check RCDs with specialist test equipment to ensure they trip out within 200 milli-seconds.