Hi All - Insulation Resistance!!!!!!

[reginald]

Sorry if i'm not in the right place, i'm new to the forum.
Just studying 2391 and having a problem getting my head around this!!
When testing a simple radial circuit we like to see 299 megohms as this shows the circuit is clear.There for why dothe regs say 1 megohm is ok???? But guidance note three say any circuit below 2 meg should be investigated??? Can,t understand why both ends of this scale are classed as ok- what am i missing??
Pleas help and put me out of my missery.

 

[Mr Mark Sparks]

i guess the reason 1meg is ok is that the circuit i considered safe at that level some meters test above and some below the 299 you mention so that is why the figure is as low as can be deemed safe

 

[brucelee]

hi mate
1M/ohm is the lowest that can be accepted But you should investigate if below 2M to confirm the reason for the low reading but 1.0M is still acceptable anything over 2 doesnt need investigating
a total ir of a installation could give you 1.2M but the individual circuits when tested seperately could be a lot higher when tested individually upon further investigation and will probably all be over 2M but when you add them all together by calculation will give a lower overall ir of 1.2 M which is Rt resistance total the sum of all resistances in paralell and this is what you would record

 

[Sintra]

Hi & welcome.

 

[CRAGS]

Hi and welcome

 

[reginald]

Thanks for your reply, perhaps its not as complicated as I first thought!! So am I right in saying that if the feed to the garage is 30 metres in 1.5 armoured with an ir of 1.5 this may contribute to nuisance tripping of the RCD???

 

[Guest123]

Welcome along.

 

[dook]

Thanks for your reply, perhaps its not as complicated as I first thought!! So am I right in saying that if the feed to the garage is 30 metres in 1.5 armoured with an ir of 1.5 this may contribute to nuisance tripping of the RCD???

What are you testing IR between? L-N, L-E or N-E?

 

[reginald]

L-E but all are similiar readings between 1.4 & 1.6 meg

 

[telectrix]

sounds like a common neutral is causing the low reading. try with all the neutrals dissed from ther neutral bar, and make sure all loads are removed, including light bulbs.

 

[reginald]

Garage supply we are testing has been disconnected both ends.

 

[telectrix]

is the cable damp at the garage end? this could be the cause.

 

[jpmiff]

Hi

welcome along

 

[Kamikaze]

Welcome to the institude of electrical confusion...​