Suspect miswired light fitting...

[Wunwinglo]

Had the spare bedroom redecorated during which the light fitting was removed. When it went back up it worked OK for a minute or so, then went dim for a few seconds, and then the MCB tripped. The switched live may have been wrongly connected to neutral in the fitting (which had another N wire in the same connector) and either the incoming or outgoing N may have been on the 'live' side of the light. It was rewired and now works.

I was confused as to why it worked then failed so decided to do a check on the cct from the fuse box. With LNE all disconnected I am seeing a couple of hundred Ohms between L and N on my cheap DVM with both wires above 1Megohm to E. All light switches were off but there is a bathroom fan after the fitting with neutral plus permanent and switched live still in cct. Switching one low-wattage light on dropped it to 40 Ohms. Is it my meter reading weird things, seeing the fan, or could there be a fault? Anything else I should test or look at?

 

[PrenticeBoyofDerry]

I assume you are doing a continuity test.
If you have have circuit conductors out at the consumer unit.
I would first check the neutral conductor of circuit to neutral busbar to eliminate a shared/borrowed neutral.
I assume there was no fault before you disconnected the original fitting prior to decoration.
I would now test to identify which conductors are Live, Switch line and neutrals.
Do not assume that it was wired originally with the colour cores being that of a standard set up. And generally DIYers see colours associated to that of a neutral conductor, that are often the switch line.

 

[Wunwinglo]

Thanks for the advice. It turned out to be a transformer primary I was reading the DC resistance across. I dug out my trusty old AVO8 and the cct was only drawing 20ma although I was reading quite a low resistance with the DVM... You learn something new every day.