What is a tail?

[MikeAustin]

I have fitted 10mm2 gas and water earths and, while the floorboards are up, I want to address other wiring. My supply board is as follows:

Electric Power Supply

• MikeAustin
• 3 Feb 2016
• 1

Main board installed at purchase, September 1985. Meter updated by SWEB April 2002.

The fused box on the left has a flat twin plus earth cable, plus an extra earth, running to the consumer unit 5m away. I was thinking of updating to 25mm2 plus 10mm2 earth. These would have to be separate cables, it seems, because I cannot locate flat twin cables of this size these days. Do these cables count as tails, or am I OK just to replace the existing flat twin with separate cables?

 

[EFLImpudence]

I have fitted 10mm2 gas and water earths

They are not earths; they are bonding conductors fitted because the pipes are earthed.

The fused box on the left has a flat twin plus earth cable, plus an extra earth, running to the consumer unit 5m away. I was thinking of updating to 25mm2

There is no need.

plus 10mm2 earth.

Probably no need either but if you want to replaced it, it should be 16mm².

 

[ban-all-sheds]

I have fitted 10mm2 gas and water earths

No, you have fitted gas and water main bonding.

The fused box on the left has a flat twin plus earth cable, plus an extra earth, running to the consumer unit 5m away. I was thinking of updating to 25mm2 plus 10mm2 earth.

Why?

What size is it, and what is the rating of the fuse?

Do these cables count as tails, or am I OK just to replace the existing flat twin with separate cables?

1) Why do you think it matters what they "count as"?

2) I really don't think you know enough about electrics to be doing this work.

 

[kai]

That switchfuse looks like a wooden backed one. It appears that you have a PME supply (Three Phase) - it may well be safer to call in a professional electrician to check that there are no problems lurking around. Three phase supplies have higher PFC currents, especially in Central London, where the declared PFC is as high as 46kA on a 3 phase supply near the substation.

 

[Iggifer]

That switchfuse looks like a wooden backed one. It appears that you have a PME supply (Three Phase) - it may well be safer to call in a professional electrician to check that there are no problems lurking around. Three phase supplies have higher PFC currents, especially in Central London, where the declared PFC is as high as 46kA on a 3 phase supply near the substation.

Looks like TN-S to me

 

[PBC_1966]

Looks like TN-S to me

And to me. Or at least it started out that way - Remember that in some areas the suppliers are bonding the sheaths of old cables to the neutral, so although it looks like TN-S at the house end, it's actually become TN-C-S.

 

[Iggifer]

Looks like TN-S to me

And to me. Or at least it started out that way - Remember that in some areas the suppliers are bonding the sheaths of old cables to the neutral, so although it looks like TN-S at the house end, it's actually become TN-C-S.

Doesn't look like that supply's been touched in a while. Love the CH flow and return right in front of the supply cable!

 

[PBC_1966]

Doesn't look like that supply's been touched in a while.

Not at that end. We don't know what might have been done at the other end.

 

[JohnW2]

It appears that you have a PME supply (Three Phase)

Eh?

Kind Regards, John

 

[MikeAustin]

OK guys, some more info. The house was built in 1860, fell into disrepair and converted to living accommodation in about 1960. These electrics are at least 30 years old, because I bought it in 1985. As far as I know, it is a TN-S supply, and single phase. The other two unused fuses on the supply may indicate that was not the case at one time. The isolator switch top left does have a wooden back. It has a 60A fuse. From the back of this comes the flat twin and earth, plus extra earth going to the consumer unit in a cupboard 5m away, here:

Consumer Unit

• MikeAustin
• 10 Feb 2016

Awful, innit? ... and half hanging off the wall! This certainly needs replacing and I would like to sort the cables for it in advance, while I have the floorboards up.

Some clarification: I do know the difference between earthing and bonding, but my terminology lapsed for a moment. I did a lot of electrical work 25 years ago (somewhere else), but requirements have moved on since then. I scanned this forum to find the required cable area for connection of consumer units to the meter. It seemed that the consumer 'tails' need to be 25mm2 - and restricted to maybe 3m in length. However, I know that consumer units can be distributed around buildings with a far greater distance than this. So, I guess 'tail' applies to a connection on the supply board? And I only need 16mm2 from my isolator to the consumer unit? Also, I do not know how much spare cable there is yet, just in case a new consumer unit needs a little extra length.

 

[EFLImpudence]

The tails do not need to be 25mm²; for 60A 10mm² would do so 16mm² is more than adequate.

You will be able to get T+E or armoured if you wish.

You have a switch fuse, which is the requirement for longer than 3m.

 

[MikeAustin]

The tails do not need to be 25mm²; for 60A 10mm² would do so 16mm² is more than adequate.

You will be able to get T+E or armoured if you wish.

You have a switch fuse, which is the requirement for longer than 3m.

Thanks. Your comments are helpful and constructive. So my cable joining the switch fuse is still termed a 'tail', the cable I have at present is probably adequate - but should the earth still be 16mm2 as you said earlier?

 

[EFLImpudence]

Your comments are helpful and constructive. So my cable joining the switch fuse is still termed a 'tail', the cable I have at present is probably adequate - but should the earth still be 16mm2 as you said earlier?

Probably. Everyone would fit that nowadays.

Your supply originally is obviously TN-S but as has been said it has likely been altered externally to TN-C-S.
No one will know how effective the original earth sheath will still be.
If it has then the earthing conductor should be the same size as the neutral but then you could get away with 10mm² neutral.

 

[RF Lighting]

I'd use 16mm² split con unless it's to be flush mounted in a wall then SWA is your only real viable option.