neutral earth probs

[007paul]

hi i am in the middle of testing a installation. its tn-c-s when i drop the neutral link at the main incomer isolator i still get a dead short on earth to neutral at the dist/board. I have disconnected all neutrals and there are three neutrals going dead short to earth. I cant find where the fault is. the three circuits are old metal clad heaters but if i isolate them from the circuit it still shows dead shorrt to earth.
Can anyone help???

 

[RF Lighting]

Does the fault still show if you switch off the DP isolators adjacent to the haeters?

 

[ColJack]

but if i isolate them from the circuit it still shows dead short to earth.

unless you think that he's taking them out of the DP switch, leaving in circuit

 

[Spark123]

I think the TN-CS, the removing neutral link and all that doesn't have any bearing on the problem.

If you IR test neutral to earth and the circuit is showing a short without any current using equipment connected then the fault is on the cable or something else which is connected to it, maybe even connected up by a handy man or could be a knackered pyro or similar.

 

[007paul]

the means of isolation is by a live and neutral seperate fuses at each heater

 

[Spark123]

Fused neutrals? How old

 

[007paul]

i know its in a 25kv sub station really old.

 

[Spark123]

Why would you have TN-CS in a substation?
Is the wiring in Pyro?
If you have both ends of the cable disconnected and it is showing a N-E fault then the cable is at fault.

 

[007paul]

tnc-s from dno supply for domestic equipment. heaters are wired in singles in trunking, ill have another look tomorrow and get back with any findings

 

[Spark123]

Aye, I thought subs would all be TN-S as it isn't a big deal to have a separate neutral and earth, unless of course the 400v supply is from another remote sub.