Strange Earth Leakage issue

[Slow Blow]

Never feed an ELU from an ELU

[BlueArc]

was this problem ever resolved? I would have liked to see what the outcome was.

[DieterT]

30mA ELU feeds from 300mA ELU / 500mA ELU (hospital,agricultural environments)
But besides this, the earth leakage monitoring is one of the best ways to see what is the cause of the problem, but there are less expensive alternatives.

For one it is good to understand what operates the earth leakage unit. The reason it could be tripping is due to an imbalanced neutral (on single phase systems)
Another reason is like what was mentioned earlier, is mixed neutrals (i.e. a neutral ring circuit, one side from one E/L other side from other E/L) or crossed neutrals where only when load is applies it trips.

Possible reason that the house E/L isn't tripping then bypassing the SubDB E/L and reconnecting the supply to the MainDB E/L is because of the distance run and proper earthing at the MainDB. Therefor fault dissipates better there for not laying in the circuit causing the E/L to trip.

Step one, would be to make sure that the neutral feeding the SubDB is fed straight from the supply neutral bar. Make sure that your earth resistance is not to high and that there isn't a volt drop on the supply due to long runs.

Step two, would be like you have done to megger each supply. Be careful when meggering between live and neutral, you could pop your tester and what ever is on the other side

You can install an additional E/L unit and separate the circuits feeding under each one, try and isolate the problem. Remember, it can also be to accumulation of leakage to earth, such as what you get when a bunch of desktop computers are put together under one E/L unit. It causes it to trip due to that each power supply leaks a little bit of power to earth.

Isn't finding an earth leakage fault alot easier when it is constant?
If you say it seems to be when the pool pump runs, try disconnecting the pool pump and see what happens. Alot of times when a pool pump gets hot, it expands and water can actually leak into the router and cause an earth fault. If it stops tripping, disconnect the motor windings from the capacitor and remove the star/delta connection then megger each winding beginning/end to earth to see if there is some leakage to earth.