Discuss low IR N-E in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

S

sivoodoo

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

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.:confused:

Thank you.
 
Aico 3000 Range
This official sponsor may provide discounts for members
S

Spudnik

  • Thread Starter Thread Starter
  • #2
Looks like something still maybe connected somewhere that may have a fault.

Spur, boiler etc.
 
P

Plan

  • Thread Starter Thread Starter
  • #3
long shot as reading is high but is neutral and earth disconnected at board?
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #4
Yes disconected at board.
Removed both legs of ring at board and tested L- E, L-N, N-E.

quick responses thank you guys.
 
Last edited by a moderator:
P

Plan

  • Thread Starter Thread Starter
  • #5
you say continuity results are ok what are they might throw up some clues
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #6
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
 
P

Plan

  • Thread Starter Thread Starter
  • #7
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
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #8
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?
 
P

Plan

  • Thread Starter Thread Starter
  • #9
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!
 
K

kung

  • Thread Starter Thread Starter
  • #10
Had same in kitchen rats and mice chewing cables ! bless em !
 
P

Plan

  • Thread Starter Thread Starter
  • #11
makes a change from the apprentices though god they get really hungry some times i have to feed them sometimes once a week!
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #12
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.
 
K

kung

  • Thread Starter Thread Starter
  • #13
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 !)
 
P

Plan

  • Thread Starter Thread Starter
  • #14
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
 
Last edited by a moderator:
S

Spudnik

  • Thread Starter Thread Starter
  • #15
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!
 
Maybe a extractor fan some where, try knocking off MCBs one at a time and re testing might tell you where resistance is.
 
W

wet string

  • Thread Starter Thread Starter
  • #17
had a similar problem on a pir recently, r1 and rn ok tho, thats probably a loose connection, had a lower ir on n-e but well within spec so didnt pay too much heed, untill i connected the new rcd cu, then the ring circuit tripped, remeasured and found short n-e which was not apparent at first test, so socket plates off, break ring and retest ir in sections, during this found a small nick in neg insulation, which i repaired, problem solved. the nick was so positioned as to be out of sight at first glance and was bearing against the backbox in varying amount when socket plate tightened, trapped neg to plate screw would give same fault, the act of plugging in and unplugging could vary the ir or even give an intermitttent short. really bad news is ,couldnt really charge the client for all the faffing about to find it,
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #18
Cheers everyone the client wants a rewire now, yipee. That saves a whole load of crawling about for (no swearing) all!
 
Last edited by a moderator:
Instyle LED Lighting Specialists UK
This official sponsor may provide discounts for members

Reply to low IR N-E in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Top Bottom