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RCDs Explained

If you don't already have RCD protection contact us to see how we can improve electrical safety in your home or business.

RCDs Explained

RCDs (Residual Current Devices)

Electricity is something our lives have come to depend on in so many ways but it can also be something dangerous too! It takes only a fifth of a second for a strong electric current flowing through your heart to kill you, something which should be at the forefront of your mind when using electric power tools. Think about if for a moment: if you're using an electric hedge cutter and you accidentally chop through the cable, the electricity has to go somewhere. If the tool has a metal case that you're holding on to, and you're standing on the ground, then there's a very high risk that your body will form a "short circuit"—the path of least resistance for the current to flow through. It takes just the blink of an eye for a current that's working for you to suddenly change its direction, flow through your body and kill you! One way to reduce the risk is to use a clever protective gadget called an RCD (residual current device) which automatically shuts off stray currents before they can electrocute you, cause fires, or do other kinds of damage.

What are RCDs (Residual Current Devices)

An RCD is basically a sensitive safety device that switches off electricity automatically if there is a fault. RCD is a generic term which embraces the various forms such as RCCB (Residual Current Circuit Breaker) and RCBO (Residual Current Breaker Overload). Residual Current Devices are now firmly established around the world as a primary means of providing protection against electrocution and fires caused by electrical faults. Less than one quarter of an amp (250mA) leaking from a faulty installation can generate sufficient heat to start a fire, or if leaking through a human body for only 200mS can cause heart fibrillation and subsequent death.

How do RCDs work

An RCD protects by constantly monitoring the current flowing in the live and neutral wires supplying a circuit or an individual item of equipment. Under normal circumstances, the current flowing in the two wires is equal. When an earth leakage occurs due to a fault in the circuit or an accident with the equipment such as cutting through the cable of a lawnmower, an imbalance of current occurs. This imbalance is detected almost immediately by the RCD which in turn automatically cuts off the power before injury or damage can result. To be effective, the RCD must operate very quickly at a low earth leakage current. Those designed to protect human life are engineered to trip out with an earth leakage current of 30mA within 200mS of the fault or accident occurring. At a higher earth leakage current of 150mA, they will trip in less than 40mS. These limits are well inside the safety zone, within which electrocution or fire would not be expected to occur.

In summary RCDs are a clever and essential part of modern day electrical systems, quietly working in the background to help us stay safe!


Here is an example of where we have replaced an old fuse board with a modern RCD consumer unit to bring it up to current safety standards. In addition to changing the fuse board we also found that there were no earth bonds to the water and gas pipes which we subsequently rectified.

Old Fuse Board

Changed for New Consumer Unit With RCD Protection

Contact us at Upgrade Electrical for a free non obligation quote to replace your old fuse board with a new RCD consumer unit.


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Not one to leave reviews but feel this company deserves it. If you're after a company that gives an all round excellent package, I would highly recommend Upgrade. The team were excellent throughout our job which took 3 days, they worked really well with having children around (Very H&S conscious), very clean (always tidy) and uniformed and did the job on time with no delays even though hurdles were met having an old house. Overall, a massive thankyou to Upgrade for the pleasant experience we have had with them.



Luke Myers

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