Low insulation resistance reading

[PJW]

i've recently installed a new Consumer unit at home and will be using it as my first niceic assessment. I'm getting an insulation resistance reading of 1.7 on a lighting circuit in the osg it says minimum reading of 1 is this going to be ok?
I've discovered what section of the circuit is giving the low reading but as I've had a loft conversion recently I can't pop the floorboards to access where the fault lies and would have to cut open the ceiling to get to the cable.

 

[telectrix]

under 2 Meg, i'd be concerned.check at fittings first, and if no joy, get cutting. can you not fish a cable in the place the damaged section, maybe an alternative route.

 

[SJD]

If you can access both ends of the offending cable section (which often you can, unless there are hidden junction boxes) and can be sure it is the cable itself, then likely the cable is damaged. E.g. rodent nibbled, or damaged during the loft conversion. In which case it is only likely to get worse, in my own home I'd want it fixed.

However, in terms of avoiding any difficulty during the NICEIC inspection, you might find if you re-measured it, you got a reading of 2.1 MOhm.

 

[David M]

When you say a reading of 1.7, between which conductors? Also did you test just the circuit? or were all the fittings and switches connected?
I'd make sure it is the circuit first before you panic about pulling new cable. I'd eliminate the possibility of a dodgy fitting, switch or some kind of electronic device e.g dimmer or fluorescent

 

[PJW]

Basically I've done a test from the start of the first light fitting and the reading as should be +299 at 500v and disconetced cables at start of circuit and the reading is 1.7, we have had a mice problem recently so maybe it has been nibbled. The initial reading was low between line and neutral others 299

 

[PEG]

Could very well be damage,but do not discount many other areas of fun...for instance,were the smokes linked in during the loft conversion?
A reading of such,would require investigation,bearing in mind the installations age and recent previous readings.

 

[PJW]

sorted, was a bad connection on the first ceiling rose i disconnected all the wires and put it back together and >299 reading

 

[Pete999]

What sort of bad connection are you talking of PJW?

 

[PEG]

Must have been a "badly made off" connection,to give rise to a low IR value,a simple "bad connection" would surely only hamper impedance.

We need descriptions and admissions!

...i'm only pecking,coz a while back,an issue similar to the one discussed,came to my attention.

The cause for concern,was a break-down in the insulation,on individual conductors,at the same position on every termination. Where they curled out of an accessory,or rose,the separate conductors touched each other,as is common,but as the insulation was damaged in exactly the same place on each one,it didn't take much pressure or moisture,for the IR to fail.

The culprit,on forensic (----) attention,was the spark's apprentice,who had stripped the cables at these terminations,using one of those CK stripping multi-tools,which were doing the rounds at all the shows,years back,with the competition stripping T&E sheath and then conductors,in a second or two.

These are quite good bits of kit,but someone,must of had a go at stripping everything in sight,and consequently,the serrated clamping jaws,had picked up some deformation,which,when on the clamp side of the strip,sliced up the insulation.

 

[telectrix]

as peg pointed out, i'd also suspect some damaged insulation where you have cleared the fault by disturbing the cables.

 

[Pete999]

Come on OP give.

 

[PEG]

...First rule of IR club...DON'T talk about IR club