Meter tails over 3m

[Bobble23]

Hi all,

Just doing a newbuild where the DB will be about 8m from the cut out/meter box. 25mm tails run in conduit on the surface of the outside wall then direct through the wall to the DB inside the house. DNO have provided a (non-fused) isolator in the meter cupboard after their 100A cut out.

I feel the simplest way to keep tick all the boxes would be to put a 100A switch fuse next to the isolator. Can't fit it (possibly not allowed to?) in the meter cupboard, so would have to put another enclosure next door.

Customer is asking, based on both price and not wanting more boxes than necessary on his wall, why the DNO's fuse won't do the same job as my switch fuse. To be honest, he's building a brand new house so fifty quid for an enclosure and a switch fuse won't break the bank, but I'm struggling to come up with a good reason that he needs two identically-rated fuses next to eachother.

Any ideas, or could I just use the DNO's fuse and leave it with just the non-fused isolator?

Thanks.

 

[Lister1987]

434.3 (iv), I think is the reg you are after. You need it because the regulations say so. The switch fuse supplements the main fuse, if I under the reg correctly.

If they are adamant they don't want it then you'd note as a departure I imagine.

 

[davesparks]

To me the obvious soloution here is to have the meter installed behind the CU location instead of 8m away, or install the CU behind the meter location.

 

[Ian1981]

To me the obvious soloution here is to have the meter installed behind the CU location instead of 8m away, or install the CU behind the meter location.

DNO‘S won’t install their cables in new builds over a certain distance from the road, their meter and cabinet will either be on the front of the dwellings or just to the side within a couple of meters from the front.
If you installed the CU behind the meter cabinet then your CU Can be randomly in your front room on the back wall or anywhere really, it typically is a design nightmare in some house types.
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434.3 (iv), I think is the reg you are after. You need it because the regulations say so. The switch fuse supplements the main fuse, if I under the reg correctly.

If they are adamant they don't want it then you'd note as a departure I imagine.

That only applies where the supplier will not allow their protective device to afford protection at the origin of the installation downstream of their ocpd.
That is something I can never get them verbally or written to commit to
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Hi all,

Just doing a newbuild where the DB will be about 8m from the cut out/meter box. 25mm tails run in conduit on the surface of the outside wall then direct through the wall to the DB inside the house. DNO have provided a (non-fused) isolator in the meter cupboard after their 100A cut out.

I feel the simplest way to keep tick all the boxes would be to put a 100A switch fuse next to the isolator. Can't fit it (possibly not allowed to?) in the meter cupboard, so would have to put another enclosure next door.

Customer is asking, based on both price and not wanting more boxes than necessary on his wall, why the DNO's fuse won't do the same job as my switch fuse. To be honest, he's building a brand new house so fifty quid for an enclosure and a switch fuse won't break the bank, but I'm struggling to come up with a good reason that he needs two identically-rated fuses next to eachother.

Any ideas, or could I just use the DNO's fuse and leave it with just the non-fused isolator?

Thanks.

Are you really running the tails in conduit externally to a new build?
Why not run internally and comply with regulation 522.6.204?

 

[mattg4321]

I think it’s likely the DNO isolator might go ‘missing’ to make room for a switch fuse in the existing enclosure if I were doing the job.

 

[telectrix]

I think it’s likely the DNO isolator might go ‘missing’ to make room for a switch fuse in the existing enclosure if I were doing the job.

same here. 3

 

[pc1966]

434.3 (iv), I think is the reg you are after.

That allows for it provided the DNO agrees to it. Normally their fuse is to protect their system, not the end user!

Otherwise the various regulations require provision of an OCPD under your control, such as 433.2.2 and 434.2.1 which give the 3m limit.

 

[SJD]

Just completed an EICR on a 5 year old house, the CU in a central hall cupboard is about 8m from the meter cabinet on an external side wall. In the cabinet is a DNO-supplied isolator, immediately followed by a switch-fuse from the original contractor.

At least you have a choice of which one to switch off!

 

[Ian1981]

That allows for it provided the DNO agrees to it. Normally their fuse is to protect their system, not the end user!

Otherwise the various regulations require provision of an OCPD under your control, such as 433.2.2 and 434.2.1 which give the 3m limit.

That 3 meter limit is relevant to where the ccc is reduced due to reducing csa for example and overcurrent protection is no longer afforded by the upstream ocpd , 3 meters limit means you can install overcurrent protection on the load side upto said 3 meters as long as other conditions are satisfied.
This is not applicable to say 25 mm tails where the ccc is equal to or greater than the service fuse but an ocpd maybe needed for 433.3.1 (iii) and 434.3 (iv).
This 3 meter limit for tails has been confused with the other regulations you have quoted.
It is the supplier who will stipulate if their fuse can be used and to what length.
This is generally 3 meters as I think they have taken that from the regulation numbers you have quoted however some only allow 2 meters and I’ve been allowed 6 in the past.

 

[BruceBanner]

I

I think it’s likely the DNO isolator might go ‘missing’ to make room for a switch fuse in the existing enclosure if I were doing the job.

ts been known to happen ?!

 

[Bobble23]

Thanks all. Finally spoke to the DNO today who (verbally) said they were happy with the long tails being protected by their fuse. Not what I expected from them tbh, but the call was recorded so I'm going to leave it at that. Thanks for all your help.