Leakage clamp aids compliance with 18th Edn Wiring Regulations

Modern appliances and plug-in power supplies, by the nature of their design, generate low levels of leakage current even when there is no fault present. This becomes a problem when there are several appliances connected to the same circuit and their leakage currents add up to exceed the trip threshold of the RCD protecting the circuit, unexpectedly cutting the power at the most inconvenient times.

What are acceptable limits for leakage current and how do you know when you are approaching those limits? The 18th Edition now makes it clear; the accumulation of circuit protector currents/earth leakage currents that are present during normal operating conditions shall not be more than 30 per cent of the rated residual operating current of the RCD, e.g. a PE current of no more than 30 per cent of 30mA, which is just 9mA. This is necessary when you consider that it's not unusual for a 30mA RCD to start tripping just above 15mA.

The trouble is: how do you know when you are approaching 9mA? Computers, printers and other appliances can easily generate leakage currents in the range of 1mA to 3.5mA each.

Rather than estimate the total incorrectly, measuring the leakage current flowing in an existing installation before modifying it, is probably the most effective approach to ensure the final installation is going to be fit for purpose. The alternative could be expensive call outs in months to come. Selecting the right leakage clamp meter is critical to getting reliable and repeatable results, as many struggle below 10mA and can be prone to interference from other nearby conductors carrying higher currents.

The Martindale CM69 accurately measures currents from 0.1mA to 60A with a resolution down to 0.001mA and includes essential multimeter functions. For more information, please visit martindale-electric.co.uk to watch a video on how to make reliable leakage current measurements and troubleshoot nuisance tripping and other installation problems.