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The RCDs explained: What is a Residual Current Device? What types of RCDs are available?

  2010-04-21         admin         Advice » Consumer Units Advice
What is a RCD, and what types of RCDs are there? Via the Electrical Safety Council website there is a very helpful article/tips regarding the RCDs. First of all, a Residual Current Device (RCD) is a safety device that switches off electricity automatically if there is a fault. The RCDs are far more sensitive than normal fuses and circuit-breakers and they provide additional protection against electric shock.

Additional protection by means of an RCD can be a life-saver. An RCD constantly monitors the electric current flowing along a circuit. If it detects electricity flowing down an unintended path, such as through a person who has touched a live part, it will switch the circuit off very quickly, thereby significantly reducing the risk of death or serious injury. Using electricity while the person is wet significantly increases the risk of electric shock. If you are wet and in contact with the ground, it makes it easier for the electricity to flow through you. The RCDs can help protect you from electric shock in areas such as in bathrooms and gardens(where you may be wet).

It is very important to have RCD protection when you are using any electrical equipment outdoors. Without the RCD protection, a simple job like mowing the lawn could turn into a deadly disaster if you accidentally cut through the electrical lead(see the MK Masterseal RCD Socket Splush Proof).

RCD - Residual Current Device - Types

There are three main types of RCD: the fixed RCDs, the Socket-outlets RCDs, and the portable RCDs.
  1. The Fixed RCDsthe Fixed Residual Current Devices are installed inside the consumer unit (fusebox) and can provide protection to individual or groups of circuits. A fixed RCD provides the highest level of protection as it constantly protects all sockets on a circuit and any connected appliances. Examples of Fixed Residual Current Devices: - the Consumer Units: 17th Edition Consumer Unit, Hager 10 Ways 1 Switch 2 X 63A RCD Split Load Insulated Enclosure; - the Consumer Units: 17th Edition Consumer Unit, Hager 16 Ways 1 Switch Insulated Enclosure; - MCBs and RCDs for CU: Hager Single Module 30mA(combined) RCBO - MCB and RCD for domestic boards; - RCD for Consumer Units: Hager 25A C Type 10KA Triple Pole RCD; - RCBOs and RCDs: Wylex RCBO, Single Module SP RCBO 6A, 10A, 16A, 20A, 32A, 40A;
  2. The Socket-outlet RCDsthe Socket Residual Current Devices are built into a special socket-outlet which replaces a standard socket-outlet. This type of RCD provides protection only to the person in contact with the equipment, including the leads, plugged into the special socket-outlet. Examples of Socket-Outlets RCDs: - RCD Sockets: RCD Socket Outlet 2 Gang 13A 30mA; - RCD Sockets: RCD Socket Outlet 2 Gang 13A 30mA White Plastic; - Spurs: 13 Amp RCD, Fused Connection Unit(spur); - Outdoor Sockets: MK Masterseal 13A IP56 30mA RCD Socket Splush Proof;
  3. The Portable RCDsThe Portable Residual Current Devices plug into any standard socket-outlet. An appliance can then be plugged into the RCD. These are useful when neither fixed nor socket-outlet RCDs are available, but remember: they provide protection only to the person in contact with the equipment, including the leads, plugged into the portable RCD. Examples of Portable RCDs: - RCD Plugs: RCD Plug In Adaptor White;

The Reliability of the RCDs

The official research found out that the fixed RCDs are about 97% reliable and that this rate is improved if they were regularly tested by users. If you have fixed RCD protection, you can rely on it to not only reduce the risk of electric shock to you and your family, but also to reduce the risk of damage being caused to your property by fire caused by faulty wiring or appliances.
Important: Although the Residual Current Device protection reduces the risk of death or injury from electric shock, it does not reduce the need to protect yourself, your family and your property by having your electrical wiring checked at least every 10 years. If you think there is a fault with your wiring or an appliance, stop using it immediately and contact a registered electrician.
Tips: A good tip is to always test your fixed RCDs when changing to and from daylight saving, as many electric clocks and timers have to be reset anyway.

Testing the Residual Current Devices - testing the RCDs

  • It is strongly recommended that you test all the fixed and the socket-outlet RCDs regularly (once every three months) by using the ‘test’ button built into them. The manufacturers recommend that portable RCDs are tested every time you use them.
  • Do not hold the test button in for a long time if the RCD does not trip. If the RCD does not switch off the supply when you use the test button, get some advice from a registered electrician.

The UK standard for the safety of electrical installations

In July 2008 a new edition of the UK standard for the safety of electrical installations, BS 7671: 2008, came into effect. This standard now calls for virtually all circuits in new or rewired homes to be provided with additional protection by means of an RCD.

Read more about the BG Electrical - RCD protected wiring devices and the RCDs – Residual Current Device, the principle of operation, or purchase online the above mentioned RCD protected devices.