Low Insulation Resistance reading of 0.63 MOhms , what does this indicate?

[telectrix]

it's all hypothetical as without being on site without test gear it's guesswork.

 

[TheSilverSpider]

Thanks to all for your responses, Much appreciated.

 

[Powerhouseelec]

When you split the circuit you may find they have taken a feed of the ring for something.

 

[telectrix]

When you split the circuit you may find they have taken a feed of the ring for something.

could well be. a lot of moisture in cannabis farms. could be the answer.

 

[Octopus]

on a ring testing Insulation Resistance L-N shows 0.63 Mohms
but L-E is ok.
I checked with the home owner that nothing was switch on, nor plugged in still.( its a 3 bed semi, looked every nook and cranny)

Is that kind of reading tell tail of anything causing that in particular, or is it a case of next visit to investigate each socket and feed to/between it individually?

Reason is they are getting random trips of the RCD for that circuit. BUT on a different circuit (hot water tank) MCB it was tripping out the RCD only when switching on the heater element , BUT NOW isolated that, and it still ocasionally trips same RCD when i.e. turn on toaster (happened once) or garage lights (happend once), also a few times when no appliance/switche were touched, both on different circuits but same RCD.

I've checked the trip out times and manual function of that RCD:

1/2: a/c tripped out, reset and never tripped on this setting after re-trying later numerous times.
1/2: d/c didnt trip

1: a/c 34ms
1: d/c 29

5: a/c 9
5: d/c 7

Its an MK RCD standard usual, Megger 1552 on 30mA setting

Heater tank circuit tested ok, and kitchen ring tested ok.

Thanks in advance

I'd say there is something connected you haven't found

 

[PEG]

How far round the dial did you IR test it? Lets hope it was'nt the hamsters lung-function machine :yesnod:

 

[Deleted member 9648]

What murdoch said...there will be a load still connected somewhere....have you checked the loft? L-N faults on T/E wiring are pretty rare and in my experience are always a missed load.

 

[SirKit Breaker]

Just wondering how l-n fails before l-cpc or n-cpc considering it has no insulation and is between l and n?

Cos the CPC does very little most of the time, somewhere between nothing and 30mA, until something goes bang, then it works very hard, but not for long, a bit like me!

Cheers........Howard

 

[stylus]

What was the IR between N and CPC ?I am with the two lads who suggest there is still a load on the circuit.maybe you could tong test to prove
Did you do a ramp test on the rcd to see what value it was actually tripping at when testing X1

 

[skydog23]

.65Mohm is about bang on the resistance of a neon indicator. L-N,
L-E would be clear.
0.4-0.7 would indicate that a neon at a fsu or emergency light is still present.
Did you notice any on your visual inspection ? They can be found in sneaky places like the hot water cylinder cupboard feeding the emersion heater.
Just a thought ?

 

[skydog23]

My bad, sorry just re-read and you've been to the hot water cylinder

 

[LittleHelper]

A rewire of the given circuit may be in order but i think its best to break down the circuit and test each leg to see if there is a faulty leg as all you would have to do is replace that leg if all other legs are good. That is of course after everything else has been eliminated (faulty socket, Neons, loose connections etc). More than likely there is somthing connected and thats your job as an inspector to determine that. Also you can get some wacky situations where part of the lighting circuit is connect to socket er.....anyway!! Goodluck
James

 

[TheSilverSpider]

.65Mohm is about bang on the resistance of a neon indicator. L-N,
L-E would be clear.
0.4-0.7 would indicate that a neon at a fsu or emergency light is still present.
Did you notice any on your visual inspection ? They can be found in sneaky places like the hot water cylinder cupboard feeding the emersion heater.
Just a thought ?

the home owner was avidly looking and checking that there was nothing plugged in, no neons, no tv booster or anything in loft. even after i checked to try and find something.
But i will investigate and progress in stages; half the circuit, check the legs,,,etc

thanks

 

[TheSilverSpider]

What was the IR between N and CPC ?I am with the two lads who suggest there is still a load on the circuit.maybe you could tong test to prove
Did you do a ramp test on the rcd to see what value it was actually tripping at when testing X1

...it was normal..between N - CPC... reading >299Mohm

 

[markc123]

the home owner was avidly looking and checking that there was nothing plugged in, no neons, no tv booster or anything in loft. even after i checked to try and find something.
But i will investigate and progress in stages; half the circuit, check the legs,,,etc

thanks

Try smash the IR at LN-E.

That's the way to do it IF there's hidden equipment vulnerable to test that can't be located and/or isolated. Do that, and then see what the reading is. There's a hole load of stuff vulnerable to test - what you've mentioned, dimmers, PIR's, RCBO's, luminaires - i know this is a socket circuit, but things can get fused down....

If not you'll just have to split it as suggested and work your way from there - the time consuimg process of fault finding awaits. However, this being L-N i'd start at each accessory, instead of testing legs - as someone has previouslly said 99.9% of the time a L-N is going to be at an accessory point.

Best of luck.