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What is an RCD?


A residual-current device (RCD) is a safety device designed to switch off electricity automatically if there is a fault. RCDs are far more sensitive than normal fuses and circuit-breakers and provide additional protection against electric shock. It will constantly monitor the electric current flowing along a circuit and if it detects electricity flowing down an unintended path (ie 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 whilst 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. RCDs can help protect you from electric shock in areas, such as in bathrooms and gardens, where you may be wet. It is important to have RCD protection when using electrical equipment outdoors. Without it, mowing the lawn could become very dangerous if you cut through the electrical lead.


What are the main types of RCD?


Fixed RCDs: These are installed in the consumer unit (fuse board) and can provide protection to individual or groups of circuits. A fixed RCD provides the highest level of protection as it protects all the wiring and the sockets on a circuit, and any connected appliances.


Socket-Outlet RCDs: 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: 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.


How much will RCD protection cost?


A plug-in RCD can cost as little as £10. A fixed RCD will cost more, but will provide a greater degree of protection to help keep your family safe. Installation costs will vary, so at S W Bishop Electrical, we recommend getting several quotes before proceeding.












If you already have RCD protection in place and would like the system testing to make sure it is working to specification, please contact me and we can arrange a safety check of your home and advise you on your installation and test to make sure it’s working correctly and meets current legislation.


So you already have an RCD - do you test yours?


Industry research shows that, although most homeowners test their smoke alarms regularly, they do not do the same with their RCDs. At S W Bishop Electrical we recommend that you test yours every three months.


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’. When tested, the RCD should switch off the power to the areas of the home it protects.


The RCD (or RCDs) in your consumer unit may not cover everything in your home, such as the lighting circuits, so it’s a good idea to check - while the RCD is off - which sockets and lights are no longer working, showing that they are protected by that RCD.


If your RCD does not switch off the electricity supply to the protected circuits when the test button is pressed, or if it does not reset, get advice from a registered electrician.


Current regulations state that a split load consumer unit (fuse board) should be installed.  Split load means a fuse board with 2 RCDs each, protecting a certain number of circuits.


We at S W Bishop Electrical always install fuse boards that comply with, or exceed the current regulation requirements.


Instead of having RCDs to protect a given number of circuits we prefer to use RCBOs.  An RCBO is a combination of an RCD and an MCB.  The problem with dual RCBs is that if a fault occurs on one circuit, this will cause the RCD to trip and you will lose supply not only


to the faulty circuit, but all the circuits protected by that RCD.  However a fault on any circuits protected by an RCBO will not affect any other circuit.  


What should you do if your RCD trips?


If yours does trip. it might be something simple causing it so there are some basic checks you can do yourself using a flowchart (Please click here for the flowchart) Here at S W Bishop Electrical, we recommend you keep the flowchart somewhere near to your RCD for convenience in a crisis!


Here's an important trade secret and one that can save you cash:  If your RCD does trip don't just switch off the sockets - pull out the plugs as well.  Nine out of ten times it will be an old appliance that is causing the trip, so you might not need an electrician, just a new toaster!


At S W Bishop Electrical, we recommend your household should have RCDs fitted to EVERY circuit in your house to protect from the dangers of fatal electric shock.  If you would like more information regarding RCDs please contact me and I will be happy to discuss how RCD’s can keep your home safe.


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