And returning to
@matlob problem. The main point, he is the landlord, not the tenant or homeowner. So he has no idea what the tenant has done. So back to the picture
View attachment 372823 fault can be lights, water heater, storage heater, kitchen sockets, or shower. Of these, the water heater and storage heater likely only active at night, likely off-peak only, so resetting the RCCB (RCD) assuming it will reset, does not really tell anyone what the fault was, we have an array of kitchen sockets which could have had anything plugged into them.
The RCD is unlikely to be faulty, but of course it could be, but to stop it happening again, some form of testing is called for. There are two ways to look for earth leakage. If the RCD does not reset, then we use a DC tester, this puts 500 volt DC on the circuit, and measures the resistance, and in general we look for over 1 MΩ. The problem is we are testing with DC, so capacitive or inductive leaking can result in a much higher leakage when using AC. (Machine often called a Mega and not really a device a DIY person can safely use.)
So if it does not trip, we use a clamp-on ammeter, we are allowed 30% back-ground leakage, so the limit with a 30 mA RCD for all circuits is 9 mA, clearly the meter must be able to measure 9 mA, so needs a scale with 1 mA increments. However, unlike the insulation tester, this tester does not require the user to open the consumer unit to do basic tests. I show here
View attachment 372830 how one can clamp it around the tails between the consumer unit and the electric meter and in this case show a total of 8 mA leakage, and turning the MCB's on/off one can work out what leakage is down to which circuit, so it can be safely done by anyone.
My meter cost around £35, I had a quick look with google
View attachment 372831depending on who you get it from can cost a little more or less to what I paid, but once you have found the faulty circuit what then? Let's say for example you find the water heater is the problem, what can the landlord do then, he needs to call an electrician or a plumber, in the main both will do both the plumbing and electrical work, but what was the point in spending £35 on a tester, rather than getting an electrician in the first place.
He needs minor works certificates for the work done to keep with the EICR, so is not likely to DIY the work, if he had the electrical skills, he would not have asked the question.
For the owner occupier telling them how to DIY likely helps, not sure if it is really helping a landlord?
