RCD not tripping under test

[Octopus]

When testing RCD's at the board, its a good idea to switch off all the MCB's

 

[uksparks]

I know this sounds ridiculous but have you got your leads the right way round on your tester? I did that once whilst scratching round in an understands cupboard with a dying head torch and not enough light to realise I'd plugged them on the wrong way round. Took me ages to realise thinking, this is a brand new shower ccu so what's wrong.

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Under stairs cupboard sorry

 

[ArseyDee]

I'll just throw this into the arena:-

Is your tester set for the correct RCD type?

On my Megger, the default setting is Type AC RCD, but I accidentally changed this with one of the function buttons and it took me a while to figure out why the auto test was ok at 1/2 x, but timed out and stopped on x1.

I know this does not mirror your tripping / non-tripping issue, but it's just an idea.

 

[Midwest]

I've only just wizzed through this thread, so apologies if this has already been mentioned. Are you a DIY'er? What tests have you done on your circuits? Have you done a global insulation resistance test? A neutral to earth fault can cause an RCD not to function, especialy in a TN-C-S supply. Does the test button on the RCD function?

 

[Octopus]

I've only just wizzed through this thread, so apologies if this has already been mentioned. Are you a DIY'er? What tests have you done on your circuits? Have you done a global insulation resistance test? A neutral to earth fault can cause an RCD not to function, especialy in a TN-C-S supply. Does the test button on the RCD function?

The OP does say "he's going back next week" so I'm guessing he's a sparky

 

[Midwest]

Ok apologies, manowarcs. Just read his thread properly. But I would recommend doing IR test for neutral-earth fault, and check to make sure all appliances etc are disconnected before doing RCD test.

 

[Badged01]

I did that once whilst scratching round in an understands cupboard with a dying head torch and not enough light to realise I'd plugged them on the wrong way round

Think what you mean is that you once heard someone else had done than and you are just relaying the info ....

Is your tester set for the correct RCD type?

Ive also heard that this can happen if you're testing with the wrong RCD setting!

 

[manoworcs]

The test button on the RCD functions just fine, I think I ruled out it being a problem with the RCD. There's clearly a problem with the wiring somewhere, I suppose I was more curious about what sort of problem would cause the RCD to behave in that way. I'd have thought any sort of earth fault would make it impossible to set in the first place...no? It is a TN-C-S system though, so I'll go back and look at that again.

I didn't do a global insulation resistance test, I did each circuit separately. Some of the wiring is old, so I was expecting a problem. Was pleasantly surprised not to get one, but that's also part of what's baffled me now.

No problems with my tester settings, I quadruple check that sort of thing any time I get unexpected results.

Thanks to everyone that's taken the time to reply though.