odd "earth" cable between 2 PME heads

1Justin · Jan 27, 2015

I have some works at a small flat (4 properties). PME. Service head has been doubled up by DNO, so that supply cable for the second head exits the bottom and feeds the second.

I find a 6mm green/yellow conductor strung between the PME break-outs of the two heads. It looks like the unusual work of a previous installer who didn't know what they were doing. (I have other earthing/bonding to sort to so here that wouldn't be surprising).

But what is odd is both break-outs have DNO seals, which were added after said cable, which implies DNO may have wanted it there (or perhaps they were laughing so much they couldn't be bothered to remove it?)

So WTF is that 6mm cable? Might it be the work of DNO? If so, - why? Note: gas/water bond should (read will..) run only to the MET off the first head. On this basis if the cable were 16mm might it be described as combined bonding/earthing for the RHS suply? - Only the PME in the supply cable between the heads is surely performing that function anyway.

(Please restrain comments on the 10mm tails and 100A fuse.. yes there is work to do here..)

Clicky for full pic..

[ElectriciansForums.net] odd "earth" cable between 2 PME heads

ImpededLoop · Jan 27, 2015

I would hazard a guess that it's incase the DNO CNE (neutral) between the service heads came loose, so it maintains both MET's at the same potential in such a scenario.

1Justin · Jan 27, 2015

That sounds a plausible reason why it may be intended. Might you leave it (6mm) ..or fit 16?

Marvo · Jan 27, 2015

Looks like main earthing not bonding so I'd leave it well alone. If you mess with it then you take responsibility for it.

davesparks · Jan 27, 2015

If it ain't broke don't fix it!

I'd be far more concerned about the obvious breach of the gas laws which has been perpetrated by an electrician there, or didn't you notice that bit?

Anthony S · Jan 27, 2015

davesparks said:
If it ain't broke don't fix it!

I'd be far more concerned about the obvious breach of the gas laws which has been perpetrated by an electrician there, or didn't you notice that bit?

Its redundant and bonded :laugh:

davesparks · Jan 27, 2015

Anthony S said:
Its redundant and bonded :laugh:

What is redundant and bonded? I assume from that comment you have visited this site in person?

1Justin · Jan 27, 2015

davesparks said:
If it ain't broke don't fix it!

I'd be far more concerned about the obvious breach of the gas laws which has been perpetrated by an electrician there, or didn't you notice that bit?

Nope.. I was more concerned with working out if there was a MET (Not exactly, but there is a choc-block out of shot where a few other random 6mm green and yellow cables connect together!), why 10mm tails were on that fuse, 6mm Earthing conductors, and if I could fix it without upsetting old people in 4 flats simultaneously (A: No).

What did the gas man do?

davesparks · Jan 27, 2015

1Justin said:
Nope.. I was more concerned with working out if there was a MET (Not exactly, but there is a choc-block out of shot where a few other random 6mm green and yellow cables connect together!), why 10mm tails were on that fuse, 6mm Earthing conductors, and if I could fix it without upsetting old people in 4 flats simultaneously (A: No).

What did the gas man do?

What actual load is on the 10mm tails? What do they connect to? What size earthing conductor does it require when calculated using the adiabatic equation?

It's not what the gas man did, that pipe is obviously older than the tails, those tails must be at least 50mm away from the gas pipe.

Knobhead · Jan 27, 2015

I don’t suppose you put a clamp meter on that “earth” jumper did you?

The only time it will cause trouble is if the two feeds are off different transformers or an open CNE. You’ll soon know if either is the case.

Guitarist · Jan 28, 2015

The fact that there are seals doesn't necessarily mean that the earth cable has anything to do with the DNO. When the meter on the right was changed, the guy may have seen that seals were missing and popped some on everything that should have them.
Just a possibility...

1Justin · Jan 28, 2015

Tony said:
I don’t suppose you put a clamp meter on that “earth” jumper did you?

The only time it will cause trouble is if the two feeds are off different transformers or an open CNE. You’ll soon know if either is the case.

No but I will check when I return

1Justin · Jan 28, 2015

Guitarist said:
When the meter on the right was changed, the guy may have seen that seals were missing and popped some on everything that should have them.
Just a possibility...

They are embossed seals, the real deal. DNO guys are usually in and out in a few minutes, so as you say, that's likely yes.