what size swa to use

That's gonna be well over a grand's worth of cable, wouldn't it be easier to find out how much the rec would charge to put in a new supply?

 

I had a new supply put on for a LL, 4 metre run, we dug the trench. £1300. But wow 140 metres is a long run...Looks like 35mm is about right but 2 core should be ok.

 

Have a look at:

https://www.tlc-direct.co.uk/Techni...230&length=90&submit=Calculate+Min+Cable+Size

It is the distance that pushes it up. Remember, you also need to consider the actual load allowing for diversity.

 

what size overcurrent protective device are you basing your calculations on?

 

35mm doesn't sound big enough to me. The last similar one I done a couple of years ago worked out to 70mm swa, that was basing it on a 40 amp supply. (volt drop etc.) I think the distance might have been greater, can't remember without looking back through my records. Have you checked it with the TLC cable size chart? Best to TT it all, the swa armour and the far end circuits.
I suggested the client getting the supply moved, the DNO wanted 12 grand!

 

It will be 35mm. You need to budget for a suitable switch fuse at the cutout end and enclosure at the CU end to make the SWA off in. There's no way you need 3-core though. Use 2-core. You'll be TT-ing it at the bungalow end.

 

Thinking about it now I believe the job i'm talking about was 220 metres.

 

I meant to say "at least 35mm". That'd be from a 60A switchfuse. But there's many a 3-bed terrace house run from a 60A fuse on a loop-in, loop-out supply.

If the demand is too much then use LPG cooking.

 

A few quick calcs and 35mm looks to be okish based on a 63A OCPD with regards to recommended max volt drop as it ever so slightly over but TBH you will never be pulling 63A. 1.365x63x140/1000=12.03V. 35mm 3 core would give you an R1+R2 of around 0.15Ohms......1.048x140/1000=0.14672. Two core would give you an R1+R2 of around 0.42 which would be no good for an 80A bs88 fuse. IMO you would be correct to use 3core or up the size of the SWA and use 2 core which ever is cheapest if your TTing the far end.

 

That would be daft IMO....For one a perfectly good DNO provided earth would be better for the distribution circuit side of things and two being TT the chances are you would never achieve stable TN values so would need to be on an RCD........RCD trips and customer has to trot 140 meters to reset it.

 

Would it not also depend on the Ze and the earth type at the origin?

 

No because the calculated R1+R2 is already over the 80% maximum EFLI value so added to Ze whatever the earthing arrangement its going to be even more over.

 

Mate, I'm not sure if I'm missing something blindingly obvious but to me it's a submain so it would have be within the max Zs at the other end, which would include the Ze. So I don't get why you think otherwise. I mean, if it's a high Ze at the origin, he may not be able to comply with the Zs unless he fits and RCD at the origin, which aint really a realistic option.

 

Yeah that was my point, using two core SWA and the armour as the CPC would produce a Zs that was higher than the maximum permitted EFLI so wouldn't be acceptable.

 

So I don't get why that should make any difference using 3 core. The OP hasn't put up the Ze so without knowing this how can you make that judgement?