low IR N-E

[sivoodoo]

Hi all,

Just done a quick test on a ring for a friend, the results are as follows.
Continuity tests are all fine.

Insulation Resistance:
Line - Neutral = >299 MΩ
Line - CPC = >299 MΩ
Neutral - CPC 39.6 MΩ

Where should I begin in finding the problem with the N-E low IR.

Thank you.

 

[Spudnik]

Looks like something still maybe connected somewhere that may have a fault.

Spur, boiler etc.

 

[Plan]

long shot as reading is high but is neutral and earth disconnected at board?

 

[sivoodoo]

Yes disconected at board.
Removed both legs of ring at board and tested L- E, L-N, N-E.

quick responses thank you guys.

 

[Plan]

you say continuity results are ok what are they might throw up some clues

 

[sivoodoo]

here are the continuity results:

r1 = 0.44
r2 = 1.35
rn = 0.55

(R1+R2) at all socket outlets were between 0.38 (min) to 0.46(max)


Thanks

 

[Plan]

you say its ok but r1 and rn have different readings its a ring so they should be the same r2 should be higher (assuming 2.5 t&e installation) due to higher resistance, code 3 im afraid further investigation required

 

[sivoodoo]

yup just realised that r1 and rn are 0.1Ω difference and as far as I can remember isnt the maximum supposed to be a difference of only 0.05Ω
Yup further investigation required.

What could be a cause of this, a screw catching the neutral someplace?

 

[Plan]

could be mice chewing on cables for all i know (sorry but with out seeing it pretty hard from where im sat to say thats yours problem)
but what i would check first is all appliances un plugged, neons turned off, isolated all spurs (test later if needed) etc then re test. if that dont work split ring (think of it as two radials) and re test. in theory one radial will be faulty one will be ok. keep splitting 'faulty radial' till you find the 1. previously un noticed fuse spur with neon and dodgy connections! or 2. bad leg of cable that the mice have been eating!!!!!!
have fun!

 

[kung]

Had same in kitchen rats and mice chewing cables ! bless em !

 

[Plan]

makes a change from the apprentices though god they get really hungry some times i have to feed them sometimes once a week!

 

[sivoodoo]

Thanks Plan, and welcome to the forum!
I shall be going back in a couple of days to have a play around, the house is empty so I can take my time, thanks for the advice.

 

[kung]

Dont know what attracts them to cables ! pvc ? emf ? knowing their being a pain in the rear ? (your not feeding me ir'll stop your cooker !)

 

[Plan]

They are nearly as adorable as cheeky unobservant lazy apprentices, but as all sparks know these apprentices are a urban myth!!!!!!

No idea why they go for them warmth from overload boredum dares from their mice friends

 

[Spudnik]

They gnaw at anything they can get hold of to sharpen their teeth.

Back on topic, i have in the past had clear IR results only to find that cables had been chewed.

A little test for you to try is to cut off a length of say 2.5 and put 500V on it.

Then strip away chunks of insulation down to the copper so that its well damaged and test again.

See what the result is!