Consumer Unit Tails

[Rick Hughes]

Question on behalf of neighbour.

He has a 3ph PME supply, he still working on his build so has a temporary supply box (DP switch, MCB, RCCD and pair of sockets)and earthed via Earth rod.

I recommended he installs a a 3ph switch fuse, taking the meter tails and then from that he can feed his garage 3Ph units as well as single ph domestic supply.

His Consumer units are about 8m cable run away from meter (and intended switch fuse location) ... he went to TLC and they provided his with a 3 core cable (non armoured) to create the switch fuse to Consumer unit link.

I was surprised that this cable has 3 core - brown, black & grey ......

Is it permissible to have grey as the earth conductor ? ........I have only used cables with bare earth wire and sleeved to green/yellow.

Is Grey the approved earth core for high current cables ?

[charles]

that's the 3 phase colours. He should have got a 5 core cable.

As I understand it, you can use any colour provided it is appropriately sleeved at the ends.

[Martin Bonner]

I think that's a 3-phase cable without an earth. Brown, black, and grey are phase colours (with blue as the neutral).

I think at this point in the system, earth is supposed to be a separate conductor.

No. green+yellow is.

I think he's got the wrong cable.

[Tim Watts]

On Thursday 22 August 2013 14:25 Rick Hughes wrote in uk.d-i-y:

Yes - he can do this. Sleeve the chosen earth core with green/yellow sleeve or tape. Sleeve the neutral blue and use the brown as is.

It's what you might do with 3 core SWA using one of the cores as a parallel earth to the armour.

Talking of which - are you sure he should be using anything other than SWA cable? This feed is not (presumably) protected with a 30mA RCD so will have to follow onerous routing rules - ie be surface mounted or > 50mm deep below a wall surface or in earthed metal conduit or trunking.

[Andy Wade]

This is for a single-phase distribution circuit for the house CU, so only 3 cores are required.

Yes, with the proviso that a single-core green/yellow conductor can't be used for any purpose other than earthing and/or bonding. Marker sleeves must be used at all terminations and identification should be /preferably/ along the whole length. Using a 2-core cable and separate CPC would have been a better choice here.

The grey core, sleeved blue, should be used for the neutral, not the earth. This is understood as conventional practice. Use the black core, appropriately sleeved, for earth.

I trust the OP's neighbour is aware that this cable must be surface wired (clipped direct or in conduit with appropriate derating). Being non-armoured and not RCD protected it cannot be buried in a wall without additional mechanical protection.

[ARW]

Now I am wondering what cable the OPs neighbour has got. Hi-tuf would be my best guess.

The earth need not always be green/yellow, it is allowed to over sleeve a core with green/yellow sleeving.

Cheers

[Andy Wade]

Or NYY-J (again), which seems to have replaced hi-tuf? (But TLC only list it up to 6 mm^2 on the website.)

Agreed.

[ARW]

So it's not just me wondering if the 6mm cable (or whatever cable TLC sold) is fed direct from the cut out and therefore possibly fed direct via a 100A fuse?

[Tim Watts]

On Thursday 22 August 2013 20:42 ARW wrote in uk.d-i-y:

He said switch-fuse - but did not qualify the fuse rating.

[Rick Hughes]

Switch fuse is 3 x 63A

I went and checked and cable is actually armoured, he had just cut them back and put heat shrink on ends.

This is a single phase only connection over to the CU's

Any time I have bought 3 ph cable it has been red, blue yellow not the brown, black grey .... guess I'm not used to the new colours now in use.

I'll pass on the advice - # sleeving black with Gr/Yel # sleeving Grey with Blue # correctly terminating cable at either ends with armoured cable glands. - one direct to switch fuse box ... - other to a termination box along side CU's - only armour wires terminating (and earthed) conductors continuous to CU's

Cable is surface clipped to concrete wall and concrete ceiling, so no problems there ... not buried anyway.

Thanks all

[Tim Watts]

On Thursday 22 August 2013 22:26 Rick Hughes wrote in uk.d-i-y:

OK - then the SWA needs to be capable of carrying 63A *and* it needs to meet the required tripping time for a L-N and L-E short at the for end against the 63A fuse (for a distribution circuit).

It also needs the armour earthed at the supply end - and ideally bonded to the wire carrying earth at both ends for good measure. Failure to earth the armour would be a regs failure.

[ARW]

"Oh dear" said the polite electrician.

[Tim Watts]

On Friday 23 August 2013 18:22 ARW wrote in uk.d-i-y:

Oh go on - let's have the professional translation...

[ARW]

Work it out for yourself:-)

[Tim Watts]

On Sunday 25 August 2013 09:41 ARW wrote in uk.d-i-y:

Did it rhyme with Toothless clucking punt?

[spuorgelgoog]

Unless the polite electrician has a lithp, it'd probably be closer to Juiceless Clucking Punt.

Owain

[John Rumm]

And, since the supply is PME, and he plans to export the suppliers earth, then it will also need to function as a main bonding conductor to allow the equipotential zone to be extended into the outbuilding.