Insulation resistance problem

[Schoe1]

Hi all i was wondering if anyone could shed some light on my problem. Came to test a ring circuit today L-L 1.23 ohms N-N 1.23 ohms E-E 1.98 R1+R2 0.73 then i did my insulation resistance tests L-N 500 ohms N-E 500 ohms then L-E 0.00. Nothing plugged in, only a few sockets connected the rest in junction boxes while the plastering is finished. Is there any obvious reason for this reading, how could i narrow down the problem? All the tests were carried out from the consumer unit.

Thanks very much

Chris

 

[Pete999]

Hi all i was wondering if anyone could shed some light on my problem. Came to test a ring circuit today L-L 1.23 ohms N-N 1.23 ohms E-E 1.98 R1+R2 0.73 then i did my insulation resistance tests L-N 500 ohms N-E 500 ohms then L-E 0.00. Nothing plugged in, only a few sockets connected the rest in junction boxes while the plastering is finished. Is there any obvious reason for this reading, how could i narrow down the problem? All the tests were carried out from the consumer unit.

Thanks very much

Chris

500 ohms then you have a problem, any Neons, loads connected, or are you reading your MFT wrong? were you testing IR on the IR setting?

 

[bigspark17]

Is this a new install or an eicr on an existing installation?

 

[Leesparkykent]

megohms or ohms? you have a short L-E....screwed/nailed through cable etc.

 

[ruston]

Plasterers water in your jb's or the back boxes, sockets wet,fly leads pulling your reading of Mohms down

 

[Schoe1]

Sorry 500> Mega ohms

 

[davesparks]

At a guess I would say that there are two different faults, the one causing the 500ohm readings and the direct short.
I say two faults as having a precise 500ohm reading twice is so extremely unlikely that it's almost certainly the same fault causing both.

Just follow the usual fault finding procedure of logical division of the circuit to find these faults.

It would be interesting to know what has caused the 500ohm fault though as it's such a precise round number and faults generally don't conform to such things.


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[Schoe1]

it is a new installation

 

[Schoe1]

no loads connected, no neons,not reading the MFT wrong, and testing at 500 volts

 

[Pete999]

Sorry 500> Mega ohms

You meam MEG OHMS

 

[Schoe1]

I didn't have long to investigate today, quickly split the ring and tested as two radials got o.oo reading again on both L-E

 

[Pete999]

I didn't have long to investigate today, quickly split the ring and tested as two radials got o.oo reading again on both L-E

What scale were you testing at Res or IR?

 

[Schoe1]

Sorry miss type yes Meg ohms

 

[Schoe1]

What scale were you testing at Res or IR?

Sorry Pete not sure what you mean, I was testing the Insulation resistance at 500 volts.

 

[Pete999]

Sorry Pete not sure what you mean, I was testing the Insulation resistance at 500 volts.

Don't know if it's me but your description of the readings you are posting are misleading, to help us/me help you, you need to be more explicit when describing your readings "I tested as 2 radials and got 0.00" don't mean a lot you have to admit, sorry if I come across as a git, but I don't mean to honest.

 

[telectrix]

sorry if I come across as a git, but I don't mean to honest.

C'MON PETE, WHY BREAK THE HABIT OF A LIFETIME?

 

[davesparks]

I didn't have long to investigate today, quickly split the ring and tested as two radials got o.oo reading again on both L-E

The go back and test it when you do have time.

 

[Schoe1]

Don't know if it's me but your description of the readings you are posting are misleading, to help us/me help you, you need to be more explicit when describing your readings "I tested as 2 radials and got 0.00" don't mean a lot you have to admit, sorry if I come across as a git, but I don't mean to honest.

Sorry not a problem my fault. So the insulation resistance readings test at 500v

L-N = 500>megohms (reading fine)
N-E = 500> megohms (reading fine)
L-E = 0.00> megohms

Quickly split the ring circuit and tested as two radial circuits and on both radial legs I got the reading again of 0.00> megohms which i wasnt expecting. If there was a break in the cable i should be getting a reading on one radial circuit.

 

[bigspark17]

Is this a new install.???

 

[Schoe1]

Yes its a new install.

 

[bigspark17]

Yes its a new install.

Well assuming you are the one who installed it you would know if there are any hidden outlets with something still connected, in which case sounds like its time to split the circuit down half by half until you find the culprit. Keep us posted with your findings. Could well be a pinched live in metal back box

 

[Richard Burns]

I assume there are no USB integrated sockets or surge protectors in circuit? If there are then it might be worth testing at 250V to see if the fault appears to clear.

If you are getting 0.00 MΩ it is often worth changing to low ohms and see if the result is a short or if the value can give an indication of the type of connection.
If you also get 0.0Ω on continuity you know it is a direct contact.

Because you are getting this reading on both side of the ring it sounds like either a cable manufacturing fault or a repeated installation error where someone else was unaware of the the cable location and has damaged it in all directions. however this seems unlikely and may just indicate a wiring error on some accessories.

 

[PEG]

It also may assist,to describe how you separated the RFC,how and where it was tested. It seems unfortunate that the same identical fault should appear on both halves.

If the fault is described accurately,it should take only one more splitting of the RFC,and the re-testing of the now disconnected six cable ends,to determine whether it is a fault,or a testing error.

Accurate terminology and result nomenclature,is vital. It is not "picky",to pull anyone up,on mistakes of this nature.

If you took your pregnant missus on holiday, to a foreign land,and asked regarding medical assistance,you would not be thrilled to find out it was 100 miles or 100 minutes or 100 pounds away...

With an accurate description of a circuit layout,together with test methods,and results,a fair guess can be attempted,at possible issues,and additional methods to apply.

 

[hightower]

Probably a daft suggestion, but sometimes the daft ones are the best ones - you've removed your temporary links at the board (sometimes installed line -> cpc to measure R1+R2 of other circuits) if you used them?

 

[bigspark17]

Probably a daft suggestion, but sometimes the daft ones are the best ones - you've removed your temporary links at the board (sometimes installed line -> cpc to measure R1+R2 of other circuits) if you used them?

The OP has stated its a ring final circuit, test links betwenn R1 & cpc would only be used on radial circuits.

 

[hightower]

The OP has stated its a ring final circuit, test links betwenn R1 & cpc would only be used on radial circuits.

Hence why I said "to measure R1+R2 of other circuits" - the scenario I had in mind:

OP puts temp link in to measure all his R1+R2's (new install, could be lots of circuits). Then does his rfc tests (end to end and R1+R2) and then terminates the cables back in the mcb etc. Then he comes along to test IR as a whole board (which is acceptable) forgetting he has a temp link, which would give him a dead short line->cpc.

I know it's a long shot, and very unlikely, but it's a valid suggestion in my mind still and it has cost me nothing to put it forward.

 

[andyb]

You meam MEG OHMS

Well mega means a million Pete.
I'm sure both are acceptable.

 

[SparkyAndGeorge]

Did you have any look finding the fault? Did you try completely splitting the ring to every individual point and testing every single cable run? Have a good look at every point on the circuit, I had a similar fault once, turned out when one of the sockets was being pinned back into the backbox the socket pin caught on one of the live conductors and caused a nick! And it wasn't me before anyone says anything!!

 

[Risteard]

Well mega means a million Pete.
I'm sure both are acceptable.

Whilst it is usually Mega for millions only Megohms is correct for referring to millions of Ohms (Megaohms is NOT correct).

 

[Schoe1]

Yes found the problem yesterday morning, it was a plaster board screw straight through the wire which the plasterer have carefully placed. Problem solved, thank you to all who gave useful advice.