Electrical installation in my garden workshop

[pompeysprk]

My Garden workshop is wired , 2 x 20a rings, 1 x 6a light, protected by

48amp rated rcd. the rings supply a 2kw rad and a computer desk with periferals. The power is fed from a 32a mcb on my main house distribution board . Recently i lost power in the workshop, however there was no tripping of any protective devices. I subsequently tripped and reset the mcb and the rcd in the workshop and the power was restored . Intriqued with this i isolated all the conductors from the mcb(house) and carried out some insulation resistance checks and open/closed mcb operation checks which were all fine . However when i connect the main connector back to the mcb but leave it switched off and carry out the same checks the open circuit characteristic no longer exists when the 20 ring mcb are switched off. Closed the resistance is .2 ohms but when opened the resistance is 56 ohms where i had previously had open circuit , ?????????????????? The earth for the workshop is taken from the main house distrubution earth . I have reconnected everything in the workshop and have power available with heavy load with no problems. Whats going on.

[pompeysprk]

My Garden workshop is wired , 2 x 20a rings, 1 x 6a light, protected by

48amp rated rcd. the rings supply a 2kw rad and a computer desk with periferals. The power is fed from a 32a mcb on my main house distribution board . Recently i lost power in the workshop, however there was no tripping of any protective devices. I subsequently tripped and reset the mcb and the rcd in the workshop and the power was restored . Intriqued with this i isolated all the conductors from the mcb(house) and carried out some insulation resistance checks and open/closed mcb operation checks which were all fine . However when i connect the main connector back to the mcb but leave it switched off and carry out the same checks the open circuit characteristic no longer exists when the 20 ring mcb are switched off. Closed the resistance is .2 ohms but when opened the resistance is 56 ohms where i had previously had open circuit , ?????????????????? The earth for the workshop is taken from the main house distrubution earth . I have reconnected everything in the workshop and have power available with heavy load with no problems. Whats going on.

[Christian McArdle]

Insulation resistance checks must be done with the circuit to be tested isolated from any circuits that may have devices attached. An off MCB is NOT isolation. This means that all appliances, hi fis, RCDs etc. must be removed before the test.

With the MCB off, it doesn't disconnect the neutral. There will be loads of appliances in the house (presumably still plugged in?) that will provide various connections between neutral and earth. They're current being fried with 500V DC between neutral and earth every time you attempt a test. That assuming you even isolated the house from the mains supply. If you didn't there will be a connection between neutral and earth through your TT earthing, or the supplier's TN earthing.

Christian.

[pompeysprk]

Thanks for the info, I kinda new that the neutral was still connected but included the info in order to give a little background to the original problem. The power in the w/shop is still ok now, but i worries me that none of the protective devices were switched off / tripped and there was no power available at the time of the fault. Anyone any ideas.