How thick cable?

[Brian Gaff]

Thicker the better methinks. after all you don't want it to be under road heating as well... Brian

[Tim Watts]

It would make no difference -

The limiting factors are volt drop and lop resistance.

It's one of those cases where the absolute ability of the cable to carry current without damaging itself is actually not the primary variable.

[Tim Watts]

Quite a valid proposal as disconnect times on distribution circuits are rather longer than end circuits (5s vs 0.4s)

[Tim Watts]

They'll run a bit dim.

That is why, although contrary to the regs, I would not bother too much about a couple of % discrepancy on the volt drop - it's not leading to an unsafe condition.

[harryagain]

Further to other replies. If it's a public "lane", he's not allowed to do it anyway. Even if it's private and others have the right to use it there could be legal problems.

He would have to get a wayleave.

[ARW]

Or 10mm for a 4% drop at 20A which was good enough for the 16th edition.

And there are small changes to calculation Iz in the 3rd amendment with the introduction of Cmin.

[Andy Burns]

Yes, but where's he going to find 100m of red & black 10mm^2 SWA now :-P

[dennis]

They will last longer, be a bit redder, a bit dimmer, that's about it.

[Adrian]

Thanks, everybody. 10mm2 it looks like it'll be.

16mm2* sounds like it might even struggle to fit through the gulley he was planning on using to take it under the tarmac...

• I typed 16m2 initially - that'd DEFINITELY be overkill...

[charles]

but lots of people do. It's no less legal than overhead and probably safer.

[meow2222]

Off a farm somewhere... this much copper needs to be fully hidden so it stays there.

NT

[Fredxxx]

My understanding is that when you "design" a system you are obliged to take into account of the fittings used. If they can tolerance 5% then I don't see why you're not allowed a deviation. You are allowed deviations?

[Capitol]

Only if he tells someone in authority.

[spuorgelgoog]

There were some nice farm electrics in the recent episode of BBC The Ladykillers involving rats in the potato barn.

Owain

[meow2222]

In fact given the cost I'd look at going aluminium. Note al does need larger conductors than cu, and end connectors designed specifically for al.

NT

[Nick]

Interesting thread. The expected load is not mentioned but also there seems to be no thought for either future expansion or unforeseen temporary loads. For example he might need a load of hot water and switch on two electric kettles. Just my 2d worth but if it were me I would definitely go for 16mm. Does he have a 3 ph supply? Nick.

[meow2222]

On the contrary, the huge cable size makes it suitable for a larger temporary load. None of the loads mentioned are very Vdrop sensitive. Uprating the cable isn't cheap.

NT

[John Rumm]

As has been mentioned many times in the past, the conductor colours tell you nothing since the switch-over grace period spanned the move from

16th to 17th editions. So new colours on a 16th edition install are fine as are old colours on a 17th edition one.

[John Rumm]

Not that significant in this case alas where voltage drop is the driver.

Personally I would be happy designed to a 16th edition spec in this case and allowing 4% drop on the submain - that would let you squeeze in with

10mm2 cable.

[John Rumm]

I suspect that heat lamps are a variant of incandescent... However being within the older 16th edition spec is not going to cause any problems.

(also note that the voltage drop figures shown in the wiki assume that the cable is operating near is temperature limit due to being at full rated load - so in cases where its been oversized just because of voltage drop, and not due to current handling capacity, there is actually more latitude that at first it would appear)