Insulation Resisitance (quick question!!)

[bleach]

Hi all!

IR global test: line & neutral connected together and tested to earth @ 250v... (nothing disconnected) eventually climbs after 2 minutes to give a reading of 140Mohms. (dampness?)

When tested on 500v it just sits at 0.30Mohms ???

I have tried individual circuits in the same way but all seems the same values? Is it because nothing is disconnected as well as damp? (Its TNS 100ma rcd main board)

Thanks in advance

 

[bigbaddave]

Ive never had it when it stays low at 500v but a rising reading as you say usually indicates dampness in the cable which when you whack voltage through it

 

[BrianDB9]

Has the apprentice come back from unplugging everything and taking lamps out

 

[bleach]

Yeah, I mean it doesn't affect the present 100ma RCD. It was just a pre check before cu change but will this trip the 30ma rcd once changed over?? My tester has only been calibrated last week aswell so I'm confused.

 

[Sharpend]

Some electronic items do not like the global approach and whilst at 250v they can withstand the voltage upping it too 500v hurts them. As they are not designed to operate at 500v.
I suggest that you switch of isolators to fans, boilers, etc. even neons can give weird and wonderful results.

 

[Brightspark2]

As said check for loads giving you the false readings...

 

[bleach]

Ok -will do, thanks. There are 2 neons that might be doing this. I was under the impression that they wouldnt affect the l&n to earth test?

It looks like there is definitely dampness though. All circuits are in use and no outside lights some perhaps bathroom / kitchen circuits damp ingress.

 

[Deleted member 9648]

A steady 0.3megs at 500v is often a surge protected lead plugged in somewhere. If it was damp it would most likely climb on 500v as well.

 

[wildgoose]

The low resistance at 500v, is often caused by a surge protector multiblock that customers use for their IT or audio equipment. Find it and unplug before the 500v test.

The gradually increasing resistance reading is probably capacitance within an electronic module? Heating controllers or lights with pir's are the favourites. Both these things are unlikely to cause you a problem with a 30ma rcd but occasionally those cheap surge multiblocks will result in nuisance tripping.

 

[Octopus]

Is there a RCD socket somewhere?

 

[stuartcourt]

TV amps sometimes straight off light circuits

 

[Guitarist]

Agree with all of the above. Some equipment just can't take 500v, even to earth. Remember, it's really the cabling you are checking and any equipment should be unplugged above 250v.

 

[bleach]

Super responses, thanks people!

(No there is not any plug in rcds anywhere).

 

[wildgoose]

Is there a RCD socket somewhere?

Nice one - forgot all about those things!!!

 

[somersetsparks]

UNPLUG YOUR GLADE PLUG-INS, theyre notorious for dodgy readings to earth, normally about 0.37!