The ohmmeter used to test leakage to earth is not the same as the ohm meter used to work out what power will be used. This
is an insulation tester, it uses 500 volts, and will give one a good idea of how much current will leak to earth. It gives one an idea, but not accurate, the same as using an ohmmeter as you have done, as the resistance changes as elements heat up, and the insulation tester uses DC, and we use AC, so there will be some inductive and capacitive linking.
This
will show accurate leakage, and power used, but can't be used if the supply is tripping.
Elements use mineral insulation, which is hygroscopic, it will absorb moisture from the air, so they are sealed at the ends, if this seal fails, you may be able to drive out the water, but it will be short-lived, and will return, so the only real option is to replace.
The clamp-on meter is showing my whole house is leaking 8 mA, the RCD should trip between 15 and 30 mA, normally around 26 mA, so if I used a single RCD it would trip with 18 mA leakage, as back-ground already 8 mA. I have all RCBO's so 14 RCD's, it is a case of penny wise pound foolish to fit one RCD for many circuits, but often the problems were not explained. Only when it goes wrong, are house owners even told there was a better way.
One can of course test the RCD, here shown doing a loop test,
but the same meter will test an RCD, it can use fixed leakage, or a ramp test, the latter will show at what extra leakage the RCD will trip, and it also measures the time taken to trip, can't really measure 40 mS with a stop watch.
But the problem is the cost of the meters, the three meters shown can easily cost £250, and even to hire, because they need recalibrating after each hire, can cost £60 just to hire.
