Do i still need to add a switch fuse?

HappyHippyDad · Wednesday at 10:13 PM

The cut out fuse is 60A.
The new CU is over 3m away.
I'm not going to be putting a fuse <60A in a switch fuse.
I'm not too sure what to do?
Nothing?
Get DNO to up main fuse to 80?

Pretty Mouth · Thursday at 8:20 AM

As I understand it, omitting an OCPD on the consumer's side in this situation is a non-compliance. However, two identical fuses in series like that, bit pointless. Also, I think you don't get full selectivity between 60A and 80A fuses under fault conditions (I might be wrong on that though, can someone confirm?).

BPG4 does not code this assuming Zs is ok, and has has it as 'NC'. To quote, "NC only. A non-conformity with BS 7671 which does not give rise to danger and where improvement is not recommended and is not required to be recorded on an EICR."

PS Electrics · Thursday at 9:21 AM

HappyHippyDad said:
The cut out fuse is 60A.
The new CU is over 3m away.
I'm not going to be putting a fuse <60A in a switch fuse.
I'm not too sure what to do?
Nothing?
Get DNO to up main fuse to 80?

Just match the cut out fuse size.

efixx did a video on this and Lewden do a Switch Fuse specifically for this scenario

100A DP Fused Switch
Includes 63A, 80A & 100A fuses (22 x 58 IEC 60269-2).
New & improved range.
Extra wiring space.

Comes with 3 fuses to match the 3 standard domestic cut out sizes.

HappyHippyDad · Thursday at 7:12 PM

PS Electrics said:
Just match the cut out fuse size.

efixx did a video on this and Lewden do a Switch Fuse specifically for this scenario

100A DP Fused Switch
Includes 63A, 80A & 100A fuses (22 x 58 IEC 60269-2).
New & improved range.
Extra wiring space.

Comes with 3 fuses to match the 3 standard domestic cut out sizes.

I've just watched the efixx video, there was no mention of what to do when you have a 60A fuse in the cutout. They just showed the standard 63A, 80A and 100A fuses.

mainline · Thursday at 7:57 PM

HappyHippyDad said:
I've just watched the efixx video, there was no mention of what to do when you have a 60A fuse in the cutout. They just showed the standard 63A, 80A and 100A fuses.

Match the 63a in the cut-out and locate the switched unit as close to the CU as practical without going over the 3 mtr tail rule.

7029 dave · Friday at 7:57 PM

If you know its a 60A in the cutout change it to 63A and put 60A in the switch fuse selectivity met. lol

HappyHippyDad · Friday at 10:15 PM

7029 dave said:
If you know its a 60A in the cutout change it to 63A and put 60A in the switch fuse selectivity met. lol

That's actually a really good idea Dave.
Of course I won't do it because we can't remove the fuse

brianmoooore · Friday at 11:01 PM

Given that in most cases we don't actually know what size the cutout fuse is (unless we pull it and check), and it's subject to change by the DNO, then I'd select the fuse in the switchfuse to suit the extended tails/SWA or whatever.
Chances are you'll never achieve selectivity on a short circuit anyway.

DefyG · Saturday at 7:32 AM

60A or 100A the issue is still the same where the DB is more than 3m away and we dont have much choice but to match the cutout fuse.
Mark it as a departure on the cert as selectivity is not can not be fully met.

EalingBadger · 2025-04-28T10:16:52+0100

I had something very similar after a conversation with the very nice chap from the DNO some years ago.

He agreed with me that it was mildly absurd to install a 100A fuse 250mm away from the board cutout ahead of a run of SWA down the side of a building but that "rules are rules".

richy3333 · 2025-04-29T12:12:42+0100

The Efixx video gives the relevant Regs and the 1.6x rule. I'd speak to your Scheme provider but think the answer Id to get the fuse upgraded to 100A or move the service head or consumer unit?

I have a similar problem where the installer has fused down from 100A to 80A but really to have selectivity it should be 60A. There's an issue reducing the fuse to 60A as they have an ASHP, EV, Sauna, large oven and a supply to a barn! Thing is the house was refurbished and the service head could have been relocated very easily at the time.

Do i still need to add a switch fuse?

HappyHippyDad

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Pretty Mouth

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PS Electrics

HappyHippyDad

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mainline

7029 dave

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HappyHippyDad

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brianmoooore

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DefyG

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EalingBadger

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richy3333

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