earthing

Dave Fone · Mar 4, 2009

We are working on a job where the incoming supplies two cables,live and neutral enter the service head.The neutral is fused and there is no dedicated earth point.
We need to instal a new pump and obviously require an earth.
Is it acceptable to now run an earth from the fused neutral point which know becomes a TN-C-S system rather then a T-N-S system.

Guest123 · Mar 4, 2009

Hey Dave.

I would say definately not.

How is the system earthed at the moment??

It sounds like that is a TT system and there should be an earth electrode somewhere.

The only people that can give you a TN-C-S system are the DNO you cant make one yourself because you dont know wether or not the neutral is spiked down along the line or not.

Worth a phone call to DNO methinks.

Cheers.

Dave Fone · Mar 4, 2009

The visual checks are that the service head is feed from a joint that has been crutched onto a mains feeder.
I would guess that the outer sheathing of the feeder cable is the CPC.
Not to sure if an earth electrode is used as there is no sign at all of an earth cable.

Any ideas?????

Guest123 · Mar 4, 2009

Hey.

Seems strange that.

Have you taken a Ze reading?? this may give you an indication of what type of earthing system you have.

Are there any D.B's you can open up to see if there is an MEC in there somewhere.

Is it a new service head??

Deffo worth contacting your DNO to find out what the score is.

Cheers.

Dave Fone · Mar 4, 2009

The service head is about 1970`s ish and there was lighting and power connected to it via a consumer unit.
Like I said no earth but only live / neutral.

Any suggetions

Spudnik · Mar 4, 2009

You really do need to get shot of that fused neutral ASAP.

These were done away with along time ago.

wattsup · Mar 5, 2009

If the N is fused, then it is beyond normal (it does happen in certain situations) ...but very unlikely in the case you mention.

I would convert it to conventional and bridge the neutral, but you may need to check that all feeds in the installation are not switching neutrals, rather than line. It could well be you have neutrals switched rather than live ...a mine field if a big installation.

I have seen it before, we were lucky in that all switches were double pole

Guest123 · Mar 5, 2009

Hey.

Ring the DNO and explain that you have on old cut-out with a fused neutral and that you'd like it changed as it is now unsafe.

If there are no other obvious signs of a main earth then I would definately install an earth rod.

Cheers.