R1+R2 continuity both ways

[shinypen]

Hi. Testing an old lighting circuit today after a c/u change. First few readings were all fine. Then on one rose I got a reading of 0.5 ohms switch closed (fine) and 186 ohms switch open.

Is this indicative of an insulation problem or something else? I did an IR test and got 0.75 ohms but it was a bit rushed and couldn't be sure it wasn't just an error. That is very low surely? I'll do that again tomorrow.

I'd be grateful for suggestions!

 

[Deleted member 26818]

Could be an insulation problem, or it could be a fluorescent fitting?

 

[shinypen]

Thanks. A fitting wouldn't give a continuity reading both ways though would it? I need to be sure of the ir test first I guess. Also it's rcd protected (tested fine) and that's not tripping.

 

[Wilko]

... I did an IR test and got 0.75 ohms but it was a bit rushed ...

Hi - IR unlikely to be able to read that low, so perhaps repeat that one? Maybe something else connected - smoke alarm or some neon?

 

[Pete999]

Hi. Testing an old lighting circuit today after a c/u change. First few readings were all fine. Then on one rose I got a reading of 0.5 ohms switch closed (fine) and 186 ohms switch open.

Is this indicative of an insulation problem or something else? I did an IR test and got 0.75 ohms but it was a bit rushed and couldn't be sure it wasn't just an error. That is very low surely? I'll do that again tomorrow.

I'd be grateful for suggestions!

IR Test 0.75 ohms are you sure you have that right, it's always best practice to do the testing prior to any CU changes

 

[shinypen]

It's just a lighting circuit so no neon and disconnected the smoke alarm. I did rush it so just closed all light switches and tested ir between line and cpc. IR could well be an erroneous reading but the continuity reading I repeated again and again.

 

[davesparks]

With an IR reading so low you have presumably left the circuit isolated?

Why did you rush the testing?

 

[shinypen]

It's just a lighting circuit so no neon and disconnected the smoke alarm. I did rush it so just closed all light switches and tested ir between line and cpc. IR could well be an erroneous reading but the continuity reading I repeated again and again.

Sure you're right. It's my c/u and the old tiny wylex board was packed full and the frame was falling apart from woodworm! Decided to just change it and pick up the peices afterwards.

 

[Octopus]

What was your Ze ? and Zs at the fitting?

 

[Richard Burns]

If Neutral and earth are connected in the CU bars and the main switch is closed then when the light switch is open the meter could measure a resistance loop, via the supply neutral earth connection, through the load and this could give a high reading of the sort of level you have measured.

 

[telectrix]

i assume the 0.75 ohms IR is a typo and you meant Mohms?

 

[HandySparks]

Did you leave the lamps in?

 

[shinypen]

Ze @ board was 0.2. R1R2 was 0.5. Didn't directly test as didn't want to energise it.

The ir must have been an error and I'll look in to it more tomorrow. Was 0.7 ohms nor m ohms! Most likely I'm just testing a lamp or something although as I say would ir line to cpc pick up this?

The continuity issue I'm sure about (that's what made me jump to ir test) so I'll dig further tomorrow. Just wondered if anyone magiclly had a solution from their experience!

 

[telectrix]

if you has an IR reading of 0.7 ohms, that would equate to 343A. surely that would cause a hell of a bang.

 

[shinypen]

Exactly! It's been running fine prior to my c/u change. I'm sure the continuity reading is right and pretty sure my ir reading is wrong which leaves me confused! Looks like I'll be doing some head scratching and floor boars lifting tomorrow (after I do a very well considered ir test).