Frustrating, intermittent earth fault

[hartdev@hotmail.com]

When I am not sure of which circuit is tripping the RCD I usually wire up a seperate DB board a have made for this purpose.
Its basically just a board with a bunch of earth leakages (RCBOs would be better), I supply my sub test board with a mains supply non rcd protected and give each circuit its own EL, i have the earth leakages numbered and ask the client to make a note of which tripped.
Once I know the circuit I check every nook and cranny of that circuit.
I have on more than one occasion found a socket needed changing although I could not pick up on the fault by testing.
I'm not sure if they are available but I have a new easier idea to test clients appliances cause they never listen when I ask them to unplug an appliance to help the process of elimination. I plan to buy an RCD with a 10ma tripping current or close thereto and wire a plug top and socket to it, then clients can plug their appliances in and tell me if it trips over night etc ( this RCD should trip before the main RCD).
... but clients never want to hear its the appliance fault lol they would rather lie and get me to come have a look and pay more than buy a new kettle x)