Leakage clamp measures up to the 18th Edition

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. When several appliances are connected to the same circuit, their combined leakage current may exceed the trip threshold of the RCD, cutting the power.

The 18th Edition wiring regulations 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% of the rated residual operating current of the RCD e.g. a PE current of no more than 30% 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 an effective approach to ensure the final installation is going to be fit-for-purpose. Selecting a suitable leakage clamp meter is key to getting reliable and repeatable results. Martindale says many struggle below 10mA and can be prone to interference from other nearby conductors carrying higher currents.

The Martindale CM69 measures currents from 0.1mA to 60A with a resolution down to 0.001mA and includes multimeter functions.

A video on how to make reliable leakage current measurements and troubleshoot nuisance tripping and other installation problems can be found at: http://martindale-electric.co.uk/.