Nuisance RCD tripping

Ever had a problem with nuisance RCD tripping?  It’s one of the most common faults, often leading to repeat call outs. A good quality leakage clamp meter and some background knowledge can save a lot of time and frustration in fixing the problem.

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 causing the power to cut out unexpectedly.
To reduce nuisance RCD tripping that is not due to a fault, but the result of cumulative leakage currents from appliances, the 18th Edition Wiring Regulations includes specific maximum values for protective earth currents (Regulation 531.3.2).  This is a great help in identifying when division of the installation is required.