Low insulation resistance reading neutral to earth

[paulc01689]

Evening all,

Very new to this forum so please bear with me if this has been answered before, I have had a look around the site and can’t seem to see an answer.
Anyway I have fitted a spur onto an existing ring main and when it comes to test it, all test readings are coming back fine except the insulation resistance test between neutral and earth?
Line to neutral is fine >299Ω
Line to earth is fine >299Ω
But neutral to earth is coming back at around 6.8Ω
I have isolated the circuit being tested so that this is the only one being tested, I have checked each socket outlet for a possible pinched conductor but all seems fine. And have run out of ideas.
Any help or suggestions anybody has would be very much appreciated.
Many Thank
Paul

 

[Jason Smith]

Have you tested your spur separately from the ring main ?- see where the fault is first, in your spur or the ring.

 

[paulc01689]

Yes I have tested the spur and that seems fine, so it must be on the ring somewhere.
There has been an extension to the house and the ring main at some stage but without pulling up carpets and floorboards I can’t see if there are any connections other that at the socket outlets.

 

[Jason Smith]

Extension been built ? turn all the lights on in the house, then turn of the ring main Fuse/MCB. See if any lights dont work, or other minor appliances. - yes builders do bog straight of a ring to the lights, usually with alive to switch, but do this test and we go from there.

 

[paulc01689]

Thanks jason will try that and let you know what happens.

 

[cbw]

Something sup bonded into the ring on a PME and your not totaly isolated?????

 

[Hawk81]

i would split the ring at each socket and do an insulation test on each cable so i could narrow it down to 1 cable.

 

[Jason Smith]

remember ALL lights in the house, not just the extension, etc etc etc.

and enquire of the customer if there is a telley vision booster unit in the loft as well.

i would split the ring at each socket and do an insulation test on each cable so i could narrow it down to 1 cable.

The lights test doesnt even involve the use of a screwdriver, at this stage, and we can always step things up after.

 

[Hawk81]

The lights test doesnt even involve the use of a screwdriver, at this stage, and we can always step things up after.[/QUOTE]

i was just trying to give him a few optiions so he does not have to keep coming onto the forum to find out what to do next.

 

[Jason Smith]

Thats right mate, he needed to know your suggestion as well because he would of been there all day I expect, and its always better to start with the cheapest and simplest possible fault find. Another one is to re test after pulling the sockets forward, and to dry out the socket nearest the kettle, re testing in between.

one of the things about fault finding is that wonderful thing called hindsight, cor, could of saved myself loads effort if I had done so and so first etc. IMO.

 

[james hanley]

the neutral and earth are connected together at the substation,just a little suggestion you might want to think of.anything connected together will have a low resistance its called continuity.

 

[james hanley]

another thing to to think of is a cable sheath could be damaged between earth and neutral on any part of the ring a megger test at each socket point should find this if your reading between two points is low then the cable between them could be damaged but this would only be if some other workers were working and replaced floorboards a nail could have possibly nicked the cable or a cable runs down a wall and a picture has been put up and again a nail could damage the cable again you will need to megger the circuit. hope you find your fault mate it can be a major headache. jimbob

 

[GStueyXR]

the neutral and earth are connected together at the substation,just a little suggestion you might want to think of.anything connected together will have a low resistance its called continuity.

What James said...

 

[ringer]

the neutral and earth are connected together at the substation,just a little suggestion you might want to think of.anything connected together will have a low resistance its called continuity.

So to confirm this would you turn off main incomer, disconnect main earth, then test between the Earth and Neutral bars in the CU?

 

[james hanley]

how did you get on with your prob mate ?

 

[james hanley]

that is one way of verifying it ringer mate

 

[telectrix]

also test N/E with and without main bonding connected. surprising what plumbers can do when you let em loose with a blowlamp close to cables.

 

[andekoch]

do you have RCD's on the circuit?
try disconnecting your earth and neutral in the board to make sure you are not picking up a N-E fault on another circuit eg the immersion. also a continuity check between your disconnected E and the rest of the E's and yout N and the rest of the N's will confirm no supp bonding issues or borrowed N issues (with main switch off mind).