IR variable results new install.

[Big Man]

Any ideas gratefully received.

I'm testing a new ground floor extension. Brand new lighting circuit. Live switches. Only feeding jcc fgled6. Continuity is fine. 0.33 at furthest point. Circuit disconnected from the cu I've had readings from 88MOhms to >299MOhms line/cpc. The others are fine. Being <1Mohm I became paranoid and began testing each leg. Each leg comes back >299MOhms but when I start bunching the cpcs into the terminal or croc clipped IR reading begins to drop off. It's wired in 1mm with 22 downlights the load being 1.8amps if they're all on. Ceiling void is insulated celotex and cable clipped direct or capped and in plaster. Multiple two way and intermediate switches.
It's not too hot today 23 degrees ambient but reasonably humid as tiling has been laying the large floor space.

Any ideas as I want to go home now!

 

[Big Man]

The lights aren't connected at the moment hence why I'm still here. Today's job was to get them all connected and the builders beginning to roll his eyes!

 

[malcolmsanford]

Have the walls just been plastered?

 

[Big Man]

They've been plastered but they're dry enough to have a mist coat put on in the majority of the room with no obvious damp plaster patches visible elsewhere.

 

[Baker1988]

Have the walls just been plastered?

Agree ^^^^ if the walls are still drying from the plaster it could be effecting you readings

 

[Baker1988]

Has a screw on the switches just caught line wire when it was screwed back, it may not be all the way through the insulation thats why you getting different readings from line to cpc

 

[Big Man]

If that is the case with the low uncertifiable readings do I just grit my teeth and put down the highest I've had????
its not the best situation I've found myself in.

 

[malcolmsanford]

Honestly I know it's pretty hot at the moment but plaster still takes a bit of time to cure and go off, and what you wrote would indicate to me that your getting these spurious reading via damp plaster.

Now you never heard this from me but if you have RCD protection on the circuit, bypass it and fire them up for a while. I'll be betting your results improve within a few hours

 

[Richard Burns]

You state you have a minimum of 88Mohms, but then say it is less than 1Mohm.
If you have 88Mohm as your lowest reading then just go home.

 

[Big Man]

Didn't hear a thing!! ;-)
It crossed my mind but they drill dead test dead test dead test.
Hmm I'll start fitting the lights then. Could be worse they're push fit!

 

[Brightspark2]

Switch them on and test again at a later date...to see if it's damp etc...

Its still 88Mohm at the moment...

 

[Octopus]

When you wired the lights were there any areas where the builders could have easily damaged the cables?

 

[davesparks]

If it is all brand new wiring then are you sure you want to accept 88Mohms? For an old installation ok, but brand new?

This is where an analogue IR tester is really useful, you can tell by the needle movement whether it's just damp or actually something untoward.

How long did you test the circuit for? was it a quick test and go or did you test it for 1 minute or at least wait until it had fully stabilized?

 

[jaypp]

Are the low IR readings on just one circuit or did you test with other circuits? What was R1+R2 as I make 0.33ohms for R2 in 1mm less than 20m which seems odd for circuit with multiple intermediate and 2way switches? Did you IR test when operating switches to see if that narrowed it down? Sounds like you've had a long day, under pressure and I would imagine if you returned tomorrow you'll 'kick yourself'! Good luck!:smiley2:

Edit, were cpc's connected at board as it seems to say 'circuit disconnected at CU' or was this after low readings

 

[Big Man]

If it is all brand new wiring then are you sure you want to accept 88Mohms? For an old installation ok, but brand new?

This is where an analogue IR tester is really useful, you can tell by the needle movement whether it's just damp or actually something untoward.

How long did you test the circuit for? was it a quick test and go or did you test it for 1 minute or at least wait until it had fully stabilized?

Totally lay agree with you re results

ive got a digital analogue display it flits about all over the place or creeps up slowly all the way to >299MOhms