You asked: I’ve been having a lot of trouble recently with nuisance tripping of RCDs and RCBOs. It’s often difficult to trace the source of the problem, especially when it’s intermittent. Do you have any suggestions?
Megger says: The must-have tool for this job is a good earth leakage clamp meter, like the new Megger DCM305E. This will measure earth leakage currents as small as 0.001 mA without the need to make connections to the circuit under test. And it has a really great new feature – peak hold. This means you can clamp the meter around the live and neutral conductors of the circuit under test at the distribution board, then go round the site switching on and off the appliances fed from this circuit. When you go back to the meter, this will show the maximum earth leakage current. Peak hold will also help you trace intermittent faults. Leave the meter clamped on a circuit for a while and, when you return, you can read the peak leakage current, even if it only lasted for a short time. Another big bonus is that as well as measuring small earth leakage currents, the DCM305E can be used for general purpose current measurements up to 100A, and it gives true RMS (TRMS) readings that are unaffected by harmonics in the supply system.