120mm to 25mm connection

[tony rowan]

Hi, I have a domestic job coming up that requires a 100A supply but it's 260mts from where the metered supply will be installed.
120mm 3 core supply SWA cable (260m long, 120mm 3 core due to voltage drop)
My problem is, how do I connect the 25mm meter tails to the 120mm SWA cable at the meter end & also how would I terminate back to 25mm tails at the consumer unit end?
I know that I could use a300A 3 phase TP & N fused isolator but trying to find a cheaper option for the client.

I have considerd a bus bar chamber or 300A TP&N isolator?

any suggestions would be appreciated

Regards
Tony

 

[freddo]

I've used this sort of thing in an enclosure before to change from a larger to smaller cable:

 

[brianmoooore]

I did a similar job to this several years ago, using 90mm2 SWA. May have been 4 core.
I fitted ring terminals to the 90mm2 conductors and the 25mm2, bolted them firmly together inside a plastic adaptable box, then filled the box with resin. The adaptable box was smaller than you might think.

 

[DefyG]

300A TP&N isolator

Did you mean switch-fuse or thinking of relying on DNO's cut out fuse for protecting the distribution cable?

 

[westward10]

Just looked, not necessarily cheaper. Check you calcs and run all options!

Wasn't looking at cost but the ease of smaller csa. That aside the vd has not been assessed correctly.

 

[JD6400]

We use these with heat shrink , either in an adaptable box or a bit of 4 / 6 inch trunking as a chamber .
They are set to shear off at the correct torque.

 

[Rockingit]

For that kind of money, three things strike me as worthy of investigation:

1. Ask the DNO to price for a closer installation point;

2. Conductors in parallel;

3…. slightly out of the box thinking here, but, use a matching pair of LV to MV transformers and do the long run in 11kV

 

[Yozza19]

Done something similar before got two units made by ec services in Bradford double pole mccb front end and a at dwelling end was small bus bar set up got both for around a grand to my exact spec

 

[pc1966]

Thanks for the reply, The client has taken delivery of the 120mm 3 core SWA.

OK so they are kind of committed to the cable sizing now!

I did consider a resin torpedo joint (this may be an option?) but I don't think this option would work with the meter box/cupboard

I really doubt the resin joint would fit in there at all!

But you can bury it and just take some 25mm (or 35mm if saving a few mV drop) from a buried resin joint in to the DNO cabinet.

 

[pc1966]

3…. slightly out of the box thinking here, but, use a matching pair of LV to MV transformers and do the long run in 11kV

I suspect going above LV is a whole lot of trouble for most folks and would really push the job back to the likes of the DNO who have HV approved persons.

It all seems a done-deal now, but they might have been better to have gone for a smaller 3-phase supply. After all 40A/phase would match the total 100A single phase supply and less issues of volt drop. However, no idea what the additional DNO cost or standing charges would have been.

 

[Rockingit]

I suspect going above LV is a whole lot of trouble for most folks and would really push the job back to the likes of the DNO who have HV approved persons.

It all seems a done-deal now, but they might have been better to have gone for a smaller 3-phase supply. After all 40A/phase would match the total 100A single phase supply and less issues of volt drop. However, no idea what the additional DNO cost or standing charges would have been.

Would be an interesting conundrum for Part P / DI’s, though! Not even a departure from 7671 as 7671 wouldn’t apply to that bit….. Interesting.

 

[pc1966]

Would be an interesting conundrum for Part P / DI’s, though! Not even a departure from 7671 as 7671 wouldn’t apply to that bit….. Interesting.

Indeed!

You could step up to something like 400-0-400V for the link and still be within sane normal LV voltages for most switchgear, etc, but it would really take a bit of computing for the transformer/installation cost versus the cable costs.

 

[westward10]

Cable that size you are either looking at an mccb in an enclosure at the source or a Glasgow switch-fuse. Personally it would be a 315A switch-fuse with an extension and down rate the factory fitted fuses to 100A. Same the other end but replace the fuses with links.
I have just been on a site where a 400A supply was required to a new building but due to cost the new head was fitted to the perimeter of the site, here a Schneider NSX board was fitted and parallel 150.0s connected from a 400A mccb.
Unfortunately big cables require big switch gear.

 

[pc1966]

I have been impressed by the Schneider Square D Quadbreak fused-switches, but they are fairly compact considering so as you say you really would need an extension box to get the cores fanned out and aligned with the terminals.

You might get away with a 250A one down-rated with 100A fuses, but having taken a quick look I'm really struggling to see any specifications from Schneider on the max cable capacity or BS88 size to see what choices would be supported.

From memory the 100A uses M8 bolts, but by 250A it would have to be something like M12 and matching lugs / crimp tool, or those shear-bolt ones shown in one of the above posts?

EDIT: Found this:

https://www.rselectricalsupplies.co.uk/images/webupload/products/downloads/Quadbreak%20tech%20and%20dimensions-31-10-2016-11293.pdf

Has 200A & 250A as M10 and max 120mm, then 315A is M12 and up to 400mm.

I just can't begin to imagine how hard 400mm is to wrangle!!!

 

[pc1966]

This sort of thing:

250A TP+N Metal Fused Switch

Rated for 240V and 415V

www.cef.co.uk

You could use one line and the non-switched neutral link for single-pole isolation, but for DP use then use two of the line terminals but have one with a link instead of the fuse.

 

[pc1966]

Come to think of it, if you bought a TPN fuses switch for the feed and (e.g. the SQB2503K above), and the switch-only version for the consumer end (SQB2503L), you would have a spare link from it for such a trick without buying any more.