Best way to parallel 25mm/35mm singles

Mark42 · Feb 15, 2023

Hi

I'm installing two new sub-mains. I need to parallel some of the supply cables.

It's the main incomer in 5 x 25mm, with 5 x outgoing 25mm tails to the adjacent DB, and an outgoing 4-core 35mm SWA going off to another building a long way away.

I will terminate in a 300 x 300 x 75mm metal box. What would others use to make the connections inside this box?

I thought about line taps screwed to the back plate, or five of these tails blocks. But if feels a bit unwieldy. Is there a better way?

Thanks, Mark

[ElectriciansForums.net] Best way to parallel 25mm/35mm singles

James · Feb 15, 2023

I would normally prefer to put a distribution board in.

pc1966 · Feb 15, 2023

Don't you want and/or need (a) some means to isolate each supply, and (b) some form of OCPD or fault protection for the longer sub-main?

Flanders · Feb 15, 2023

What about using a small ryfield board

Mark42 · Feb 15, 2023

Thanks. I didn't explain this well.

The incoming 5 x 25mm runs from a 3P 50A MCB in the main DB at the origin. That protects this cable, and anything else (so long as the CSA is big enough) downstream, without further protection. I dislike cascading MCBs for multiple sub-mains as it's usually impossible to provide discrimination.

And there are already 11 DBs in this install - which is my own house and workshops - and I don't want any more!

But ... there is already a DB (Hager 3P 12-way) next to my proposed joint box, to be run from the outgoing 25mm tails.

I really don't want to ram two heavy cables into the supply side of that DB's main switch, even using crimp tags, as that little 100A switch is not designed for it; and taking the 35mm lines out from yet another MCB would be, in my opinion, poor practice.

Effectively I'm running the two downstream sub-main DBs from the one 50A mcb in the main board. How is that different from running from a bus bar chamber? I just want a simple solution.

My question was how best to terminate. I'm a bit rusty, and there may now be connectors I've never heard of.

pc1966 · Feb 16, 2023

If you are looking at 35mm/25mm paired in to a 100A switch then yes it is a bit of a tight fit.

If you are looking at using a DIN box then you can get terminals for it that have bolts so doubled-up lugs are an option, for example:

1SNA190001R2000 Entrelec Power Terminal Two Studs 2.5 - 35mm Cbl D35/27.FF

Buy 1SNA190001R2000 Entrelec Power Terminal Two Studs 2.5 - 35mm Cbl D35/27.FF | Order By 1pm For Same Day Shipping | Log In For Better Pricing

www.cse-distributors.co.uk

You also get terminals that can be paralleled, so 2 * 2-way for 4 cables, for example:

https://uk.farnell.com/entrelec-te-connectivity/1snk516010r0000/terminal-block-din-rail-2pos-10awg/dp/1750565

https://uk.farnell.com/entrelec-te-connectivity/1snk916303r0000/terminal-block-jumper-bar-3-pole/dp/1750625?MER=sy-me-pd-mi-acce

You can also get DIN mounted distribution not unlike the Henley blocks as well, but not always for 35+25 sort of splits:

1561770000 | Weidmuller Distribution Block, 2 Way, 50 mm², 70 mm², 300A, 1 kV ac/dc, 600 V, Grey | RS

uk.rs-online.com

Mark42 · Aug 2, 2023

Six months later I got around to finishing this job, as digging 200m of trench did not fill me with enthusiasm. I eventually rented a chain trencher which I'd not used before. It's a marvellous piece of kit, highly recommended.
Thanks for the suggestions, but in the end I screwed four 35/25mm line taps to the box, run the uncut 35mm through and piggy-backed the 25mm on top. It's analogous to an underground branch.
I think it worked well, was simple, and reduced the number of joints.
To recap, this is downstream of a 3P 50A MCB, and is to run two DBs, one local, one 200m away.
I'm posting this conclusion for completeness, and in case this is useful to others. Plus I'm sure some will enjoy telling me I'm wrong, the job is rubbish, and it doesn't comply with some regulation or other. Carry on

.

James · Aug 2, 2023

Looks like a neat solution
as long as those terminals are rated for over 50A (would be amazed if they are not) then it all gets a thumbs up from me.

however if you are really looking for criticism, why can I see a hole to the right of the left hand cable entry?

pc1966 · Aug 2, 2023

James said:
however if you are really looking for criticism, why can I see a hole to the right of the left hand cable entry?

Well spotted! Looks like 20mm gland in 25mm punch-out?

Given the earthing nut and decent flying lead to it I guess the only issue us if it is not able to stop the gland pulling away, but that seems unlikely.

A few spare banjos might have hidden it!

EDIT: Realised it must be bigger then 20mm/25mm for that cable size, doh!

Mark42 · Aug 2, 2023

James said:
… why can I see a hole to the right of the left hand cable entry?

Ha ha! I though someone would notice that. Excellent attention to detail.

The 32mm hole I drilled in the top intersected some pre-cut 20mm entries. A remaining bit of steel sheet fell out when I tightened the gland.

I suppose I’ll have to fix that now

brianmoooore · Aug 2, 2023

Everything in that pic is much bigger than it looks at first sight. The screw heads securing the box to the wall are the giveaway.

Mark42 · Aug 3, 2023

brianmoooore said:
Everything in that pic is much bigger than it looks at first sight ...

Good point. Here's a better picture for scale.

Best way to parallel 25mm/35mm singles

Mark42

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James

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pc1966

Flanders

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Mark42

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pc1966

1SNA190001R2000 Entrelec Power Terminal Two Studs 2.5 - 35mm Cbl D35/27.FF

1561770000 | Weidmuller Distribution Block, 2 Way, 50 mm², 70 mm², 300A, 1 kV ac/dc, 600 V, Grey | RS

Mark42

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James

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pc1966

Mark42

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brianmoooore

-

Mark42

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