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essexboy

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hi

just done a insulation resistance test on upstairs ring and got the following results

P-N >299Mohms
P-E >299Mohms

N-E>0.26Mohms ??????

as you can see the N-E result is unacceptable can anybody shed a bit of light on what the problem could be or how to find out where the cause of the low resisatnce reading is...

thanks for your replys :confused:
 
A

adamh

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  • #2
is it pme or is that just a daft answer lol
 
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PAUL M

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  • #3
did you test the ring at socket or at ccu? did you remove the neutral and earth from the board to do test?
 
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essexboy

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  • #4
thanks for your responses

the earthing system is tn-s but the test was done at the ccu end on the upstairs ring circuit only not through the meter tails .2 fused spurs feeding shower pump and tail rail were isolated there is no other vulnerable equipment on the circuit so tested between L-N ,L-E ,N-E

???
 
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PAUL M

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  • #5
but did you remove the cpc and neutral from the board to do test?
 
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essexboy

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  • #6
yes paul both all conductors of both ends of the ring were removed from the board
 
S

sparkyork

not sure but could it be the fused spurs are only single pole and your getting a reading through neutral earth that way, or did you physically disconnect the pumps as well?
failed socket outlet somewhere?
something somewhere still plugged in, tv amps, etc etc

hope you get it sorted matey
 
J

jimes

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  • #8
go to what you think would be furthest away from board and split the ring will narrow it down, prev post about single pole could be it or maybe a trapped cable etc
 
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EasyFox

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  • #9
go to what you think would be furthest away from board and split the ring will narrow it down, prev post about single pole could be it or maybe a trapped cable etc
Divide & conquer :D
My money is on a doubled up neutral in backbox thats been nicked by plate screw.
 
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Shakey

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  • #10
but did you remove the cpc and neutral from the board to do test?
as a side issue you cant do that anymore

17th says insulation test between live conductors and the cpc connected to the means of earthing:confused:

cant think why, but hey, there it is its in the regs.:eek:
 
W

wayne

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  • #11
as a side issue you cant do that anymore

17th says insulation test between live conductors and the cpc connected to the means of earthing:confused:

cant think why, but hey, there it is its in the regs.:eek:
ok leave the cpc connected but take the neutral and phase out
go with easy fox ,divide up and find the trapped wire /nicked wire (known it to be caught in capping before now)
 
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tc3

  • Thread Starter Thread Starter
  • #12
as a side issue you cant do that anymore

17th says insulation test between live conductors and the cpc connected to the means of earthing:confused:

cant think why, but hey, there it is its in the regs.:eek:
Hi Shakey

do you know the reg number on that one. is it just for rings or all circuits.

thanks in advance

couldn't find my regs book before. i was just reading christopher kitchers book. p57 he says disconnect neutral or cpc.
found my regs book 612.3.1 ,can't see why, whichever is easiest would seem logical.
thanks
 
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M

mdshunk

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  • #15
At what voltage do you guys do insulation resistance checks at? When I get a really low reading like posted when I do them, I can't help but to think that I might have just blown up someone's television or computer accidentally. I never have, but my mind races for a few minutes, thinking like that. We check domestic wiring at the US typically at 500 volts.
 
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PAUL M

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  • #16
we check at 500v d.c. ,and we unplug our tv and everything ellse why we are at it.
 
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EasyFox

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  • #17
I tend to unplug everything then test at 250v as this at least gives an indication of anything still plugged in thats hidden away. If the reading is ok at 250v I bang 500v round the circuit.

Hidden items I've come across in the past:

fcu + neon behind cookerhood
Floods spured off ring final with fcu's in loft space (blew a pir on security light last week when meggered circuit :()
Tv amp in loft (either off the lighting circuit or ring)
Plug in air freshner behind bed
Tube heater in toilet taken off ring to fcu
Fitted appliances in kitchen no isolator above worktop.
Oven plugged into ringfinal.
Spur from ring final out to greenhouse feeding heaters/lights
 
S

Shakey

  • Thread Starter Thread Starter
  • #19
I tend to unplug everything then test at 250v as this at least gives an indication of anything still plugged in thats hidden away. If the reading is ok at 250v I bang 500v round the circuit.

Hidden items I've come across in the past:

fcu + neon behind cookerhood
Floods spured off ring final with fcu's in loft space (blew a pir on security light last week when meggered circuit :()
Tv amp in loft (either off the lighting circuit or ring)
Plug in air freshner behind bed
Tube heater in toilet taken off ring to fcu
Fitted appliances in kitchen no isolator above worktop.
Oven plugged into ringfinal.
Spur from ring final out to greenhouse feeding heaters/lights
Easyfox old chap

thats exactly what i teach my students to do,
and 612.3.2 specifically allows you to do it:D
 
T

tc3

  • Thread Starter Thread Starter
  • #20
finally a sensible regulation hurrah
 
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mdshunk

  • Thread Starter Thread Starter
  • #21
I tend to unplug everything then test at 250v as this at least gives an indication of anything still plugged in thats hidden away. If the reading is ok at 250v I bang 500v round the circuit.

Hidden items I've come across in the past:....
That's what I've taken to doing as well. Since we're dealing with a phase-to-neutral voltage of 120V here in the states, I'll do my preliminary check at 50 or 100 volts; whichever scale the megger I'm using happens to have. The stuff I miss are things like chime transformers, roof exhaust fans in the attic, television amplifiers, plug-in air fresheners, dimmer switches, and switches w/neon lights.

You all might find it interesting that megger checks are not required here in the US at all, at any interval. I do them myself following water damage, fire damage, or a hard lightning strike. Seems like the only prudent way to pass or fail the installed wiring following such occurrances.
 
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EasyFox

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  • #22
md you ever worked over here in the uk?
 
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mdshunk

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  • #23
md you ever worked over here in the uk?
No, but I'm pretty well tuned in to the way you all do things there. Pretty much the same as here, except you use a lot of loop feed circuits, and we're not allowed to do that here. You switch pretty much everything, which really helps with your regular testing you do of the wiring, I'm sure. You all are required to do a lot of testing on certain intervals, and we have to do *zero* testing of anything here in the states. Smart electricians do, however. Sort of a "cover your butt" type of thing. I do have a copy of the 17th edition regs, just for my own reading entertainment.
 
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greekislandlover

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  • #24
I'm sure I can think of many other books I'd rather have for bedtime reading! But it's certainly interesting to know the differences between the two countries.
 
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