Keeping up with RCD developments

RCDs are just about as common as electrical wire and GPOs these days. You'd think that the electrical trade would fully understand what they are, how they work and why they're used. But that's not really the case. Many in our industry, including contractors, wholesalers and engineers struggle to understand the nuances of RCDs.

What does RCD stand for - Remote Control Door? Really Cool Device? Ready to Catch Dummies? Really Can't Decide? Everyone in the industry knows that RCD stands for Residual Current Device, commonly known to consumers as a safety switch. The term I grew up with for it was an Earth Leakage Circuit Breaker, or ELCB, which I think is a more descriptive name, since it explains what it does.

Whatever the term, I'm sure every electrical contractor has wired in at least one RCD that didn't work, followed by hours of fault finding and retracing wiring. Why go to all that trouble? Firstly, because it's the law - RCDs must work as designed wherever they're installed. Secondly, and more importantly, you know that this little device, as annoying as it may be to rectify, could save someone's life. Conversely, it could cost someone's life if it's left not working.

But that raises another important question - how confident are you that after months and even years have passed, that RCD you installed still works as it was designed to? Conditions change that can alter the effectiveness of the RCD - the condition of the earth path, the condition of the electrical equipment and modifications (both authorised and unauthorised) to the electrical earth path.

The Wiring Rules legislate specific requirements to ensure that electrical devices, including RCDs, are installed and function safely, but this is a living document that's regularly updated to ensure it's always current on safety and best practice. In fact, we're waiting for the revised version to be released right now. ABB line protection product manager, Ian Richardson keeps up to date with the development of RCD legislation and technology and has seen the evolution of both: "The new Wiring Rules are expected to regulate the use of RCDs more stringently than before, but there isn't any definitive indication how much it will change. But when it's released, contractors should make sure they understand what's required of them when installing RCDs. There is a danger of overlooking the changes and just designing and installing earth leakage systems like they've always done over the previous five, ten or twenty years. The fact is, RCD regulations have changed since many contractors were trained on them. So if they don't keep abreast with changes in the regulations, they're likely to either install them incorrectly, or struggle with requirements they weren't trained on. Either way, if they don't keep up with these changes, the consequences could be disastrous".

Richardson refers to Appendix B of the Wiring Rules to stress his point: "If an installation had a 2.5 mm2 earth conductor instead of a 6 mm2 earth conductor, a long cable run or a high impedance was present in the earth path, then a subsequent fault current may cause the protective device not to operate correctly. The installing contractor may be deemed liable or negligent in having contributed to a person's injury or death as the installation has not met the current requirements".