RCD residual current device

What is an RCD?

What is an RCD and How Does it Work?

RCDs, or residual current devices

So what is an RCD? Furthermore, how can RCDs assist, and keep us safe?

A residual current device (RCD) is one of the best ways to protect yourself from electrical equipment. Accidents, after all, can happen. And the dangers of electricity mean that the consequences of these accidents can be severe and even fatal.

By installing RCDs into your electrical systems you can significantly reduce the risk of electric shock. The safety aspect of the RCD device is that it works by breaking the link in the electrical wiring circuit. This protects from an ongoing electrical supply and the danger of electrical shock.

Understanding what an RCD is and how it works could make a real difference to the safety of your electrical equipment, so let’s take a closer look at RCDs.

What is an RCD and how do RCDs Work?

An RCD is a safety device which is able to detect faults in electrical supplies and immediately switch the circuit off. This prevents the flow of electricity and provides protection against electric shocks. For example, a sudden surge of electricity will cause the RCD to trip out and shut down the current. As mentioned earlier, this reduces the risk of electric shock, but it also prevents the risk of electrical fires developing from faulty equipment.

The RCD unit is able to be tested with a simple press of a test button. This test button simulates a small electrical leakage to check that the breaker neutralises and switches off. A separate button resets the unit back to normal.

Types of RCDs

There are more than one type of RCD and the most common ones you will encounter are:

  • Fixed : Typically found within a fuse box, a fixed RCD delivers the best protection against electric shocks. A fixed RCD is capable or protecting individual circuits and more complex setups which are comprised of multiple circuits. This type of RCD is, given its fixed position, constantly providing protection to your circuits.
  • Portable : As the name suggests, a portable RCD can be moved to wherever it’s required. A portable RCD is most commonly used when your options are limited for installing an RCD such as on a construction site. The portable RCD simply plugs into an available socket outlet and is then ready to have an electrical device plugged into it.
  •  Socket Outlet RCD: Replacing a standard socket outlet, a socket outlet RCD provides a much safer option for working with electrical devices. They are commonly found in extension cables and used for outdoor appliances such as lawnmowers.

What would trip an RCD?

An RCD is considered a highly reliable device and will prevent electrical shocks in around 97% of all cases. Naturally, this is a success rate which is highly favourable to your well-being, but it is not a 100% guarantee. Therefore, you should always be careful when working with electrical applications and RCDs by following these best practices:

  • Test Your RCDs
    All RCDs will have a test button built into them so that you can test that they are working and will disconnect the circuit. You should run a test on each RCD every three months to confirm that they are in good working order. If the test button does not activate the trip then contact an electrician to investigate this further.
  •  Check Your Wiring
    It’s important that any electrical installations (and the RCDs themselves) are checked every 10 years. Wiring can deteriorate over time and circuits can easily malfunction, so it’s crucial that you cover every base rather than relying on the promise of an RCD alone.


An RCBO is similar to an RCD but with the added benefit of over-current protection which is integrated into the unit. They are commonly used when protection is required against overloaded circuits and circuits susceptible to short circuits. In addition situations where earth leakage might be a problem such as with large banks of PC’s


For more information on What is an RCD and the options available to you, don’t hesitate to get in touch with one of our expert engineers.

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