Limited Space For Out building supply

Oliver Luke Martin · Apr 2, 2019

Hi all,
I am looking a installing a new supply to an out building, but very limited in space in electrical cupboard.
Could you use a double pole mcb in place of a switched fused disconnect ?

If not could you please enlighten me as to why.

Thanks all.

Pete999 · Apr 2, 2019

Oliver Luke Martin said:
Hi all,
I am looking a installing a new supply to an out building, but very limited in space in electrical cupboard.
Could you use a double pole mcb in place of a switched fused disconnect ?

If not could you please enlighten me as to why.

Thanks all.[/QUOT
Not in your CU because the CU will be single pole so a DP wouldn't compute

Pete999 · Apr 2, 2019

Let me know your location I'm willing to visit and advise if you like.

davesparks · Apr 2, 2019

Oliver Luke Martin said:
very limited in space in electrical cupboard.
Could you use a double pole mcb in place of a switched fused disconnect ?

If not could you please enlighten me as to why.

Thanks all.

How big is the incoming supply and the new supply you are installing?
Possible reasons for choosing a fuse over an MCB are a high level of fault current or the need for discrimination.

Why do you need the DP MCB?

SparkyChick · Apr 2, 2019

The problem with using MCBs upfront like that is discrimination, sorry... selectivity.

When you say space is limited, how much room do you have available? A picture may help.

Charlie_ · Apr 2, 2019

Is it a sub main?
And what’s the means of protection for it?

Oliver Luke Martin · Apr 2, 2019

It will be a SWA our going. It’s the standard electrical cupboard on the outside of house. It will be straight from a Henley Block in 25mm2 to MCB then out in 16mm2 canny get a switch fuse with 40A fuse.

Dustydazzler · Apr 2, 2019

Use a little consumer unit with rcd and 40a breaker ?

Oliver Luke Martin · Apr 2, 2019

That’s an idea. But didn’t think you needed RCD protection on SWA?

buzzlightyear · Apr 2, 2019

Oliver Luke Martin said:
hen out in 16mm2 canny get a switch fuse with 40A fuse.

canny or cant.

Oliver Luke Martin · Apr 2, 2019

Don’t think you can get 40A fuse for KMF type switch and it’s a 10k braking capacity on the MCB so should ok as fault curren on site is only 4.8k
I’ll have a look when I’m back on site to see if I can fit a larger DB in

Midwest · Apr 2, 2019

Allegedly the DNO's don't like you putting your stuff in 'their' meter cupboard. Bit like fake Earth Moon landings or the Flat Earth. Could enquire with them though.

Taylortwocities · Apr 2, 2019

Oliver Luke Martin said:
That’s an idea. But didn’t think you needed RCD protection on SWA?

You don't. But just a DP main switch + 40A fuse carrier. Wylex NSC40 is an option.

123 · Apr 2, 2019

Midwest said:
Allegedly the DNO's don't like you putting your stuff in 'their' meter cupboard. Bit like fake Earth Moon landings or the Flat Earth. Could enquire with them though.

They don't, but the birds have to nest somewhere