Falling insulation resistance

[Rob Smith 643]

Yo folks,

Not sure that this isn't the second post on same topic, first hasn't appeared. Apologies if so.

Ahead of altering upstairs lighting circuit to add a couple of downlights to an ensuite I carried out the usual tests. Got odd IR results. L-N >1000, L-E >1000, N-E 10!. Did a bit of poking around in the loft and found a spider wired downlight arrangement for main bathroom downlights. JB plus wagos. Removed the arrangement and the IR leapt to >1000. Tested each leg of spider, >1000. As I added eah leg of spider the IR fell away to 10 again. This will be fundamental but it eludes me at present. Any ideas, solutions. Is this typical of spider wired downlights? I tend to daisy chain my own installs.

yours,

Rob

 

[Pete999]

Think of resistors in parallel

 

[ferg]

It could also be damaged cable that is only showing up on the IR test when in a certain position.

 

[Rob Smith 643]

Think of resistors in parallel

Thats the theory I believe is at work here but it hasn't affected L-E results...?

 

[Rob Smith 643]

It could also be damaged cable that is only showing up on the IR test when in a certain position.

Tis odd. The jb is a tad cramped. The IR reading tumbles each time I add another leg of the spider. I'll end up rewiring in a daisy chain and test it again. See what gives.

 

[Pete999]

Thats the theory I believe is at work here but it hasn't affected L-E results...?

Are the switches in the ON position when you test L-E?

 

[guest119]

N to E 10.
10 what?

 

[Rob Smith 643]

Are the switches in the ON position when you test L-E?

Yes, switches on.

 

[Rob Smith 643]

N to E 10.
10 what?

Mohms is what

 

[Pete999]

Yes, switches on.

Cables still connected at CU?

 

[Rob Smith 643]

Cables still connected at CU?

Initially but not during further testing Pete.

 

[Pete999]

Initially but not during further testing Pete.

So all cable dissed fro CU ? This JB you spoke about, have you tried testing with the circuit connected but NOT stuffed back in the JB?

 

[Rob Smith 643]

So all cable dissed fro CU ?

Yes. When connected to CU, the initial readings were L-N >1000 Mohms, L-E >1000, N-E 7.62. Disconnected the readings were the same for L-N, L-E but had imprived slightly on N-E to 10 Mohms. I realise thats a 'pass' but curiosity got the better of me. The property was rewired 4 years ago with the downlights added shortly afterwards during a bathroom refurb. Theres a cert for the rewire but not for the alteration.

 

[Pete999]

Yes. When connected to CU, the initial readings were L-N >1000 Mohms, L-E >1000, N-E 7.62. Disconnected the readings were the same for L-N, L-E but had imprived slightly on N-E to 10 Mohms. I realise thats a 'pass' but curiosity got the better of me. The property was rewired 4 years ago with the downlights added shortly afterwards during a bathroom refurb. Theres a cert for the rewire but not for the alteration.

I can only surmise that when the JB is reconnected ( thats the reason I asked if you tested with the cables not pushed into the JB ) there is, maybe some damp or something, a strange one that isn't it sorry can't be of any help other than my suggestions.

 

[Rob Smith 643]

I can only surmise that when the JB is reconnected ( thats the reason I asked if you tested with the cables not pushed into the JB ) there is, maybe some damp or something, a strange one that isn't it sorry can't be of any help other than my suggestions.

Cheers Pete, your interest is appreciated. There's some slack in the cables at the jb, I'll remake connections after a visual inspection. I'll let you know if I suss it. Rob.

 

[guest119]

Cheap plastic lampholders (overheated by now) in the downlighters maybe?

 

[Rob Smith 643]

Cheap plastic lampholders (overheated by now) in the downlighters maybe?

Cheers Boydy, I'll check them out as well.

Hate unsolved puzzles...