Humour me please

[Ramjam]

I'm pretty sure I know what size tails are supposed to be but I just want to look it up but I'm going mad trying to find the regulation in 7671 can you point me in the right direction please?

 

[DurhamSparky]

supply characteristics!! BIG HINT!!!

 

[ezzzekiel]

depeds what current they will be carrying

 

[Deleted member 26818]

There is no specific Regulation regarding 'tails'.
You would determine their size as you would any other conductor, bearing in mind the rating of the existing main fuse.
Ib < In < Iz.

 

[Ramjam]

I'm sure I've seen something somewhere which gives the size of the head fuse and the size of the tails, 60amp head 16mm tails, 100amp head 25mm tails. The onsite guide just gives meter tails minimum 25mm.

 

[richy3333]

I'm sure I've seen something somewhere which gives the size of the head fuse and the size of the tails, 60amp head 16mm tails, 100amp head 25mm tails. The onsite guide just gives meter tails minimum 25mm.

Was that in GN3?

But as said, supply characteristics...

 

[telectrix]

you are correct there. however, it is usual, in a domestic to use 25mm as standard,as that would mean that the service fuse could be uprated from 60A to 100A without replacing the tails.

 

[ian.settle1]

Was that in GN3?

But as said, supply characteristics...

The OP did say the onsite guide

 

[Lioned]

Well i have just this morning had my assessment and pleased to say got through no problems or non conformers and not even any observations,so thats a relief for another year.
I am with ELECSA and the Inspector i had has done me a couple of times before and has previously been a pain but today he was in a good mood.
Anyway the job i took him to was a CU change and upgrade main earth and main bonding, in a first floor maisonette with meter box outside.16mm tails going up metal conduit in the cavity,no way was there enough room to drag up 25mm tails but i managed to draw up a new 16mm earth off the old one so that was ok and 10mm to the gas and water was a bugger but got it all done ok.And also got an earth on the conduit in the wall.
So i was a bit worried about keeping the 16mm tails as the on site guide clearly says 25mm minimum.So i had pre warned the Inspector that it hadnt been possible to change the tails.So he says no problem as the cut out is 60 amps and he recons 'from the book' you could get 87 amps or 76 in conduit.He did also say that your looking at the load/demand ,so if your looking at a smallish flat/house so long as you havnt got a 10kw shower you could argue a case even on a 100 amp cut out,though not recommended.
So in other words if you can change the tails without too much hassle then always go to 25mm,if you have a 60 amp cut out and its a real sod to change them then 16mm is ok.