Puzzling Earth Fault

[brucyboy]

Apon functional testing or circuits and then blanket testing between the neutral and earth bars inside the board I had a reading of 0.00Megohms. This is with the main switch closed (On) and all MCBS open (off).

Don't know if it will help, but can you measure N to E as a finite resistance, e.g. using the continuity range? Just wondering if there is some way an external fault e.g. in neighbours property and via gas/water bonding could be contributing in someway (not sure it's likely, but might be good to know).

Try disconnecting each earth conductor until you find the link. ??

 

[derek preece]

Hi SJD, Yeah I thinks its service side as the fault disappears when the service isolator is opened. Bearing in mind this is TT, Close the isolator and then its 0.0Megohm between the neutral and earth bars in the DB....Its weird......

Richard Burns was correct in highlighting your confusion over this issue. Perhaps you could set up a temp board with RCBO's in if you have one lying about that might help identify which circuit (if any) is causing the problem then the householder can tell you which circuit is tripping if it is an intermittent fault not showing up with IR tests.

 

[guest119]

Ref the zero n to e reading, a possible cause.
Your side is bonded to common water/gas pipes/ steelwork so is the neighbour.
Neighbour has a n to e fault, you get a zero reading to n coming from your install/bonding.

 

[Captain Custard]

If you are taking a insulation resistance reading with the main disconnecter closed you will get virtually 0M as regardless of the earthing system the neutral is always connected to the star point of the generator which is bonded to earth to stabilise the neutral referenced to earth i.e. neutral and earth are effectively the same conductor.
I had a very similar fault some years ago caused by poor earth bonding in local property's on the same overhead two wire supply
I would suggest getting a PME terminal added costs £35 around here and if the problem persists add a 100ma S type RCCB to the supply tails and obviously retain the existing 30ma.