Low reading in new kitchen ring

[Nijinski001]

I have just tested a kitchen circuit and have a low reading for insulation resistance. 0.353 megaohm to be precise. I have checked and double checked the test just to make sure.

The guy who fitted it tells me that he split the old downstairs socket circuit using one end as the start for his kitchen ring. He then used the old 6mm cooker cable to link up the other end of the ring. In bewteen is completely new 2.5mm cable. And a fused cu of course,

The circuit seems okay in everything I can gain access to.

Any ideas what the low reading is telling me that I haven't found?

I could understand the low reading if the circuit wasn't freshly laid.

 

[pdcelec]

Is there a neon anywhere? such as fused spurs etc.

 

[Nijinski001]

1 fused spur for the cooker hood.

 

[pdcelec]

Isolate all items of equipment and retest. Are the low readings between L-E, N-E, or L-N?

 

[Nijinski001]

L-N 0.385
L-E 0.391
N-E Reading 0.00

 

[sparkybird]

Was the 6mm cooker cable brand new?? If not maybe this is your problem Not quite sure how you are getting a reading of 0.0 for N to E - this indicates that the conductors are in contact surely?

 

[pdcelec]

That is virtually a dead short. Does the mcb stay in at all! With readings like that, I would suspect a nail or screw through the cable, or a crushed cable somewhere.

 

[Nijinski001]

The cooker cable wasn't new but is only to the start of the ring. Would it have that dramatic an effect on the reading? Especially bearing in mind the ring is brand new between outlets.

 

[Nijinski001]

pdc
The MCB stays in and it's on an RCD as well. The appliances attached are working okay so it's also taking a load with no ill effects.

 

[Lectrician]

Are you testing this circuit completely isolated from others at the CU?? Disconnect the neutrals and turn off the MCB for this circuit.

N to E 0.00 suggests you are reading through the N/E link in the service head.

If you are reading N to E, then all other readings will mix with other circuit readings etc etc.

Disconnect EVERY appliance, remove the two neutrals from CU, and try again.

 

[Nijinski001]

Guys the plot thickens.

Just been back to do a new reading.
Disconnected fused spur, and cooker.

New results
P/N 1.06
P/E 0.69
N/E 0.48

Better but still not there.

Also took new continuity readings.
P/P 0.67
N/N 0.67
E/E 0.35 (??)

I opened up every socket and checked connections. Everything fine. Found a junction box under the cupboards. All connections okay. I think this has two spurs running from it as well as the ring.
I can't find the 6mm cable so this has to be under the floorboards somewhere.
Could find any crushed cables in the bits I can see.

Apart from "get the hell out of this fast" what other advice can you give on a possible solution.