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What is an RCD?

An RCD, or residual current device, is a device which is designed to prevent persons and livestock from receiving a fatal electric shock if contact is made with a live conductor, such as a bare wire, or live metal work of items such as washing machines under fault conditions. It can also provide some protection against electrical fires. RCDs offer a level of  protection that ordinary fuses and circuit-breakers cannot provide.

What do RCD`s actually do?

An RCD is a sensitive safety device that disconnects the supply automatically if there is an electrical fault to earth.


An RCD is designed to protect against the risks of electrocution and fire caused by earth faults.  For example, if you cut through the cable whilst mowing the lawn and accidentally touch the exposed live wires.

How Exactly does an RCD work?


An RCD continually monitors the electrical current flowing through the circuits it is in place to protect, If it detects electricity flowing down an unintended path, such as through a person who has accidentally touched a live part, the RCD will disconnect the circuit almost instantaneously, significantly reducing the risk of death or serious injury.

What are the main types of RCD?


RCDs can help protect you from electric shock in areas of high risk such as bathrooms and gardens, and there are various types of RCDs that can be used to ensure you are always as safe as possible.

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  These are installed within the consumer unit (fusebox), and can provide protection to groups of circuits in split load consumer units, or to individual circuits in rcbo loaded consumer units.  A fixed RCD provides the highest level of protection as it protects the wiring and all electrical accessories on a circuit, as well as any connected appliances.

Socket-Outlet RCDs

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These are special socket-outlets with an RCD built into them which can be used in place of a standard socket-outlet. This type of RCD provides protection only to the person in contact with equipment, including its lead, plugged into the special socket-outlet.

Portable RCDs

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These plug into any standard socket-outlet. An appliance can then be plugged into the RCD. They are useful when neither fixed nor socket-outlet RCDs are available but, as with socket-outlet RCDs, they provide protection only to the person in contact with the equipment, including its lead, plugged into the portable RCD.


Are RCDs reliable?

We’ve found that fixed RCDs are about 97% reliable. This improves if they are tested regularly. If you have fixed RCD protection, it will reduce the risk of electric shock to you and your family. It can also protect your home against the risk of fire caused by faulty wiring or appliances.

Remember – Although RCD protection reduces the risk of death or injury from electric shock it does not reduce the need to be careful. Have your wiring checked at least once every 5 to 10 years to ensure the safety of you, your family and your home. If you find a fault with your wiring, or an appliance, stop using it immediately and contact a registered electrician.

Don’t forget to test – You should test all fixed and socket RCDs about every three months. Manufacturers recommend that portable RCDs are tested every time you use them.

Beware – If you press the test button and the RCD does not switch off the electricity supply, then get advice from a  registered electrician.

The UK standard for safety – Since January 2018 virtually all circuits in new or rewired homes have been required to include an RCD under the latest edition of BS 7671.



How do I check whether I already have fixed RCD protection?


To check if you have fixed RCD protection, go to your consumer unit and have a look to see if there is a device with a pushbutton marked ‘T’ or ‘Test’. This ‘test’ button is part of an RCD. If an RCD is fitted, there should also be a label on or near the consumer unit stating ‘test quarterly’.

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