16mm SWA tails maybe 9 mtrs from isolator on a 100a supply, and other concerns - EICR opinions

S P · Jun 16, 2018

This has come up many times before and after a couple of hours reading previous posts I'm no closer to deciding on a code, note or nothing at all.

BS7671 allows 16mm tails on 100A fuse if demand is less than the cables CCC, I have 16mm at 94amps and the max demand is 60a.

From a previous post I've read UKPN state switched fuse OR ISOLATOR within 3mtrs.

Would you code, mention or no mention this?

Dillb · Jun 16, 2018

You are assesong the job as per BS7671, nithing else so UKPN has no bearing on it. What you have to ask yourself is will the maximum demand ever chamge in the future seeing as the incoming fuses will allow it.

Wes1000 · Jun 16, 2018

Surely if the cable after de rating is at 94A and your max demand is 60A an 80A fuse would be more appropriate?

Dillb · Jun 16, 2018

Wes1000 said:
Surely if the cable after de rating is at 94A and your max demand is 60A an 80A fuse would be more appropriate?

Yeah but we cant change that init, beside thats not the question.

S P · Jun 16, 2018

Thanks Guys,

I agree Dillb, and it is feasible as separate 6mm cable has been run for hob and oven, new home owners may decide to install induction hob and higher rating oven.

It is a gas hob atm and 13amp SFS for oven.
Oven at higher rating is probably unlikely as most modern ones are 16A max.

Either way it didn't sit right with me as I would have installed switched fuse at 80A. Still unsure on code though?

Dillb · Jun 16, 2018

Well its your call as the one signing the EICR. From what you have said as its just my opinion I would give it a C2 as you never what they may do in the future.

S P · Jun 16, 2018

Im going to try to attach photos..
Other areas of concern are:

1) Un-enclosed SWA conductors - I guess it could be argued the meter cabinet is an enclosure opened by key. so maybe C3 not C2?

2) Main earth uses gas supply = C2
From suppliers terminal they have 10mm to first earth terminal, the 2x 10mm goes to water bond, the 2x 2.5mm go to SWA amour. Nothing connects to the other earth terminal! Which holds the 2x 16mm from the SWA and 2x 10mm Gas bonds. Therefore other than the gas the earth path is the 2x2.5mm to the amour.