What is an RCD, and what does it do?


So we have spoke about the importance of having RCD’s for quite some time now.  However we’ve never explained what an RCD is and how it protects the household.

An RCD stands for Residual Current Device.  It is an essential safety device that automatically cuts off the electricity if there is a problem.  This might sound pretty boring and bog standard, and you might even wonder what the point of having one is.

An RCD is a quick mover.  It detects a problem before you even realise there is one and cuts the power in less than a split second. As an example, if you were mowing your lawn with an electric mower and you accidentally cut through the wire, the RCD would activate and save your life.  If you went out and left your washing machine running and it developed a fault, the RCD could save your home from burning to the ground.

The Merseyside Fire Service attend many call outs due to electrical faults. 231 in 2009, 229 in 2010, 190 in 2011 and 111 up to July 31, 2012.  During this period, the largest proportion – 214 – were as a result of electricity supply, cabling, wiring and plugs, followed by 77 for washing machines and 73 for tumble dryers.  During these years there were the following totals for accidental house fires for those years – 1,390 in 2009, 1,296 in 2010, 1,216 in 2011 and 661 in 2012 (up to July 31, 2012).

Many home owners around Liverpool ask me what the point of an RCD is, especially when fuses and circuit breakers also cut the power if a problem develops.  The fact is an RCD is far more sensitive and will definitely activate in the event of a problem.  A Fuse or circuit breaker is not guaranteed to react fast enough and it might be too late.

A fixed RCD device has been fitted to virtually all circuits in new or rewired domestic property since July 2008.  If you have one fitted that is great, if you haven’t it is highly recommended that you do so in order to stay electrically safe in your home.

If you have one, it is important that you test them regularly.  They are 97% effective, but in the same vain as you test your fire alarm weekly it is worth getting into the habit of testing your RCD every 3 months.  The effectiveness does of course improve if you test it.  Simply hold the test button for a few seconds and the electricity supply should cut out.  If it does not, then you will need to seek advice from a qualified, registered electrician.

There are also two other types of RCD devices that are found within homes.  These are RCD Sockets and portable RCD’s.  These should be tested each time they are used.  RCD sockets replace standard sockets and provide RCD protection for anyone using electrical equipment plugged into those sockets.  A Portable RCD is plugged into a conventional socket and this then provides RCD protection to the person who plugs their electrical equipment into the socket.  The advantage to these is that they can be moved around and used for riskier jobs such as mowing the lawn.

Remember RCD sockets and portable RCD only provide protection to the person using the appliances plugged into them, it does not protect the whole household.  However, I always say some RCD protection is better than none at all.  I always recommend to my customers around Liverpool that if they do not have the budget to install fixed RCD protection in their home to at least buy a few portable RCD’s to use, particularly in the garden.

An RCD is there to prevent death or serious injury please do use them however you can.

About the Author Scott Fitzsimmons

Scott is the director of STF Electrical Ltd. He is an apprentice trained electrician from Liverpool with over 15 years experience in all aspects of electrical design, installation, maintenance, testing and certification. A member of the IET and the #e5 group, Scott is passionate about quality and safety within the electrical industry.

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