What is an RCD?

An RCD, or residual current device, is a broad term for devices that are designed to prevent you from getting a fatal electric shock if you come into contact with something live, such as a bare wire. Moreover, it can provide some protection against electrical fires. Fuse and circuit-breakers cannot provide the same level of protection that RCDs can.

To put it simply an RCD is a sensitive safety device that switches off electricity automatically if it detects a fault specifically what is known in the trade as “earth leakage”.

RCDs are designed to safeguard against the risks of electricity-related injuries and fires. Imagine cutting through a cable when mowing the lawn and accidentally touching the exposed live wires or if a faulty appliance overheats, causing electric current to flow to earth. At the first detection of small amounts of current not flowing back to the RCD, the RCD would trip.

Example of RCD module

How do they Work?

To protect one or more circuits, a RCD watches the electrical current flowing through them continuously. They work by measuring the difference. How much current that goes out must be the same as what comes back. If it sees 2.23 amps flowing out on the phase wire but only 2.15 amps are coming back on the neutral, there is obviously some leakage current to earth and the RCD will trip. The rating they actually trip on is far smaller than this above example, small enough that the current will not cause death or serious injury.

What types are there?

Typically, RCDs come in three varieties; switchboard RCDs that are wired into your switchboard, socket-outlet RCDs that replace standard socket outlets (power points), and portable RCDs that are portable and great for working with electrical equipment outdoors.

  • Socket outlet RCD – This is an RCD that is built into standard socket outlets (power points) for providing protection to equipment plugged into the outlet and, if necessary, protection to downstream outlets. The use of socket-outlet RCDs is common practice in bathrooms and other damp areas to ensure electrical safety. You might recognize these as the outlets with the green and red buttons on them for test and resetting.
  • Portable RCD – An extension cord or appliance plugs into these RCDs (often incorporated into the extension cord) and then into the socket outlets (power points). You can move the RCD from socket outlet to socket outlet as required. Having a portable RCD is very helpful when operating electrical equipment (such as electric lawnmowers or power tools) in damp or wet conditions where your supply outlet is not RCD protected. If you’re working with electrical equipment outside, you should always use an RCD. A cable can easily be sliced by accident. Various hardware stores and suppliers of electrical equipment sell portable RCDs.
  • Switchboard RCD – These are installed at the switchboard to provide earth leakage protection to selected circuits or groups of circuits. In most cases, a switchboard RCD is the best choice, since it protects all the wiring and appliances on that circuit. Only licensed electricians or electrical inspectors are authorized to install these devices. 

The best option is typically an RCD in the switchboard because it protects all electrical wiring and appliances that are connected to that circuit “downstream”. 

Are RCDs required by law?

YES, RCDs are required by law. In 2018 the electrical regulations known as the AS/NZS 3000 underwent a big change and new stricter rules around RCDs came into it. If you are getting a new outlet installed in your house it needs to have RCD protection, if you don’t have RCDs in your house currently, you should look at getting them. They are a lot more affordable now than they used to be and the benefits of having them far outweigh the associated cost. 

Want to learn more? 

Get in touch with us today to learn more about the benefits and protection to yourself and your property that RCDs can offer.