Insulation testing earth fault... strange one

[batty]

simple answerNo

Its a standard 5 + 5 wylex split load

Theres your problem never trust them wylex consumer units. Damn have two to fit tomorow.

 

[Dane]

OK, Dane:Have you checked for continuity to another circuits CPC and or Neutral?

Don

Yes and everything checks out fine there no continuity onto other circuits.

 

[The Godfather]

Yes and everything checks out fine there no continuity onto other circuits.

OK, with the ring main connected to the CU, remove the other circuits one by one (connection by connection if you have to).

(Assuming you've not done so already)

And see at what point there is any change (If any).

Failing that, with all connected, break the ring at the sockets, one by one.

Don

 

[steptoe]

you say connected to board,

are all the circuits turned off at the board?

you could be getting a feed through an appliance to neutral which in turn is earth on your PME.

or it could just simply be a fault elsewhere, which I tend to lean towards.

connecting a cable into a board shouldnt change the readings,

are you sure you actually have both correct legs of the ring and havent mixed something up?

beaten by the Don,

also, check that neutrals havent been swapped somewhere, when the Don says disconnect other circuits I think he means all cables being parts of other circuits, ie, L N E

 

[SPECIAL LOCATION]

Removed the ring main, tested it all fine. Once the ring is put into the board it fails tests insulation resistance to any earth is around 0.04M

40,000Kohms

Not usual at all. It threw myself and another completley at first. Was loosing light by 4.30 so had to pack up and got to go back in the morning.

Going to rip the ring main apart like you say lurch....

Some how, some where that 1 piece of cable is going to earth via the building. Again, there are no other metal parts within the builing.

Cables are all in plastic capping... yes it could be a capping nail! But its must be a very wet building on the structure side to get a reading through the building like this surely?

No it doesn't need to be a very wet building for a reading of 0.4meg.

I am inclined toward Lurch's suggestion here..

either

1/ cable one conductor pierce with nail into wall structure

OR

2/ cables squashed breaking insulation allowing direct contact the wall structure.

Have you tried,

with the ring circuit all isolated from the board..

Join LN&E together stick one of your meter leads onto these joined cables..

stick the other probe somewhere into the building..

e.g.

a concrete floor

bare brick wall in the motar...

see what reading you get?

For example If I stick me Ins Tester one probe going to the earth terminal of one of the sockets in my garage..

(garage sockets metal clad in PVC conduit screwed to facing brick on garage wall.)

and the other probe on my trailer standing in the garage..

(Metal trailer 2 x rubber tyres 1 x Hard plastic composite of some sort jockey wheel)

I can get a 0.03Mohm reading!!!!!

Thats through earth CPC, Brickwork, Concrete garage floor, Rubber tyres, Axle bearings, Metal chassis of trailer.

OR stick one probe direct onto wall of my trailer tyres,

(trailer tyres less than 6 months old i.e. good tread depth)

I can get a reading 0.02megohm!!!

From the description of the isolation tests you have already done..

It's pointing toward a 'Lurcho' nail or squashed bit IMHO!



DON'T BE FOOLED THINKING MEGOHMS DON'T GO THROUGH BRICK!

:|

 

[Dane]

DON'T BE FOOLED THINKING MEGOHMS DON'T GO THROUGH BRICK!

:|

never had anything like it before though so its a very strange one to me.

 

[Dane]

Just noticed this is in the wrong section lol :coat

Any how, bit of an update, this morning we tried to get a Ze reading

Cant get anything at all.

The strange one is that its showing 240v between L and N but check L - E and get nothing.

This is a PME, could this be anything to do with it, is there a certain way to take a reading on PME?? (this is the first PME system ive worked on, and its now bugging me)

How would they be allowed to leave the meter without them getting a Ze reading to confirm earth?

I know its not what you should do, but we took the neutral cover off the main incomer and but a seperate earth in

And the reading was the same, no earth .....

Am i missing something here? Wet Fish

 

[Andy™]

are you sure its PME?

i have known DNO to install a service head with earth block at side, but nothing internally connected and TT system

 

[jl-heating]

ooohhhhhh andy ..... long time how the devil is you .

 

[Lurch]

I know its not what you should do, but we took the neutral cover off the main incomer and but a seperate earth in And the reading was the same, no earth .....

Am i missing something here? Wet Fish

I think someone is. Even if it was a TT you would still get a Ze reading if you connected the earth to the neutral block on the incomer.

 

[Dane]

[quote name='Andy

 

[Dane]

There is a big sticker "this is a PME System - a minimum of 10mm tails are required"

Ive not actually been to the job today it some one who does a bit of work for me

 

[Andy™]

There is a big sticker "this is a PME System - a minimum of 10mm tails are required"

well, that sounds like a give away as to what it is....

whats the voltage N-E? hopefully DNO havent got it horribly wrong....

 

[Andy™]

ooohhhhhh andy ..... long time how the devil is you .

you made it a long time! im good. obviously your doing so well you dont have time to come here often!

 

[Dane]

After a bit of digging and phone calls...

and some fiddling about...

There was no earth connected within the service head! Very nice! Although the earth cable was there

 

[Andy™]

which is one very good reason for testing!

 

[The Godfather]

Just noticed this is in the wrong section lol :coat

Moved.

Don

 

[jimleen]

It's neither PME, TN-C-S or TT no?

It's a newbuild. So is it flats? If so, the DNO may have just earthed the conduit going upstairs and hoped that that the gas and the water weren't run in plastic. Which may well be the case.

Seems either TNS or a Friday job to me. But I'm most probably wrong. Hell, what do you expect at this time of night? Guinness

EDIT: steam powered computer has just caught up!

 

[steptoe]

this still doesnt explain the fault in #1

can I ask how much experience the OP has,

because this is the type of instance where i really think it makes a difference.

 

[ianmacd]

Maybe a neon somewhere?