What is an RCD? Why do I need one?

what is an RCD and what does it do

What is an RCD? Why do I need one?
These are the sorts of questions I get asked all the time,
What does an RCD do?
Why do I need one?
Are they expensive?

An RCD or Residual Current Device is designed primarily for human safety, as a safety cut out to minimise the risk of injury or death from an electric shock. RCD’s work by constantly monitoring the flow of electricity through one or more circuits, and when it detects the electricity is leaking down the wrong path, making something live that shouldn't be, the RCD cuts the supply of electricity to that circuit in milliseconds. 
RCD’s reduce the risk of electrical fires by protecting you against earth faults, where insulating properties of the cable have deteriorated over time allowing the earth conductor to become live. In non RCD protected fuse boards this sort of fault often goes unnoticed until its too late.
The current wiring regulations stipulate that all domestic electrical installations be protected by an RCD, preferably multiple RCD’s.
You should be testing your RCD’s every six months to ensure that it is functioning correctly, there should be a sticker on the front of your fuse board explaining how. All RCD’s have a test button on them, simply press this button and the RCD will trip – then reset it and your done. If it doesn't trip when you press the test button you should seek professional advice from your local electrician as these are one of the most important safety features in your home.
There is no set price for providing RCD protection as each property is very different, it may be a case of upgrading an existing fuse board or it might require a full board replacement. You should ring your local electrician for a free quotation and advice.
Please remember that just because the electrics in your home appear work this does not automatically mean they are safe, your electrics should be tested periodically, this will highlight any developing faults and help to keep you, your home and your family safe.