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).

 

[Loki]

Just a thought - I know some of the the loft light switches we install on new builds have a neon light on the switch.

Michael

 

[7029 dave]

What cable?, pvc , that is a very low reading, lamps out.?Maybe something else on the circuit.TV booster etc.

 

[westward10]

Am I the only one who has no idea what these readings are all about.

 

[Pete999]

Am I the only one who has no idea what these readings are all about.

No Westy you are not the only one.

 

[7029 dave]

Am I the only one who has no idea what these readings are all about.

I am taking it he means Mohms Westie.?

 

[PEG]

I'm not brave enough,to ask what the readings were,before the board swap...

 

[Anthony_wayne]

No damp areas? Almost like there is something else in the circuit? Or when you IR'd did you have cpc on the bar still with neutral connected?

 

[dmxtothemax]

could there be a switch with built in ilumination ?

 

[Pete999]

I'm not brave enough,to ask what the readings were,before the board swap...

Get the impression that there wasn't any testing before CU change hope I'm wrong

 

[Deleted member 9648]

It always mystifies me when an (alleged) low IR is encountered that a neon always seems to get the blame. This would only happen on a L-N test, the OP has not specified what IR test has been carried out but I doubt it's L-N. Or is it OP?

 

[shinypen]

Tested polarity of incoming supply, ze@ board, direct zs and pfc of several points on system and bonding before hand. All were fine. The board was a mess and a real tangle of too short cables.

I freely admit to being new to this so as an aside is it really common practice to do a full set of tests on every part of every circuit before a board change?

In this instance it's my board and any problems that arise need to be fixed by me anyway. Surely safer and easier once a new board in place.

 

[shinypen]

No damp areas? Almost like there is something else in the circuit? Or when you IR'd did you have cpc on the bar still with neutral connected?

Thanks anthony. This is helpful. I did indeed have the cpc still connected to the bar. Hadn't realised this could introduce problems. I'll update this post at the end of the day with the results! Hopefully just that and an incorrect ir test...

 

[Pete999]

Yes it's always best to IR test before CU change why? because you are adding RCDs to the system, and any IR N-E L-E will trip the RCD, nothing more frustrating than changing CU all nice and neat, then do your testing, no bonding IR faults file:///C:/Users/Pete/Downloads/Best-Practice-Guide-1-Issue-3-(1).pdf

 

[shinypen]

Yeah can see the logic. Point taken. IR tests are such a pain though!

 

[Pete999]

Yeah can see the logic. Point taken. IR tests are such a pain though!

Even worse pain is not IR testing and the RCDs trip and you have to start ripping your nice neat CU to bits to find the fault