Fusing down a sub main to garage

[Llewelr]

Afternoon all.

Ive installed a sub main for a family friend in 10mm SWA (5 metres) from meter box to garage as they are converting to an office (x1 ring circuit and X1 lighting circuit) maximum demand in any case would be no more than 40amps.

I am aware that the SWA does not need to be RCD protected as per 522.6.100 and it's a TN-C-S supply however I would say it's obvious that this needs to be relevantly fused at the meter, my issue is the meter cupboard is already very cramped (new build) given that I've split the mains after the isolator and a KMF would not fit in there.

Any suggestions on how to fuse it down neatly/safely ?

Thanks

 

[GMES]

Hi and welcome to the forum.

 

[uksparks]

Is there space for an isolator switch?

any chance of a photo?

 

[Llewelr]

Is there space for an isolator switch?

any chance of a photo?

Thanks for the reply.

Ive just about managed to fit the earth block and the 100A Henley block in the cupboard, my only other thought was to terminate the armoured into an adaptable box below the cupboard and pop a din rail with a 40A breaker in there then 10mm T&E or singles up to the Henley block/earth block. Haven't got a photo of the meter box at present.

 

[Octopus]

How come the meter box is so small?

 

[Llewelr]

How come the meter box is so small?

Its just your standard new build meter box service head, meter, isolator but once you add earth block and Henley block you don't have any more room to mount anything on the chipboard.

Uksparks mentioned putting an isolator switch in ? I could do that below the meter box but it doesn't protect the cable.

 

[Richard Burns]

Once you want to start fusing down the distribution circuit you are again faced with the non combustible joys of the idiot IET.
Therefore anything you use should be non combustible, ahh, sudden thought, the meter box is outside the property so does not need to be non combustible, possibly.
I would use insulated and sheathed 10mm² from Henley to outside enclosure as termination safely otherwise is a nightmare.
Then depending on space you could use an IP rated consumer unit, discrimination from the garage is unlikely to be a major danger, but possibly you could use a fuse carrier in the CU instead of a breaker.

 

[rich.250]

Double pole circuit breaker in a small non combustible enclosure?
Or
Take out where it's been split and do it inside a 4mod enclosure.
One CB for each outgoing way?


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[Llewelr]

Thanks for the replies fellas, much appreciated.

Can someone just educate me on one thing (may sound silly) seeing as this is a sub main and will be terminated into a board not allowing more than 40amps anyway why does it need to be additionally fused ? Just thinking along the lines of tails to a distribution board in a dwelling in normal circumstances I.e. 16mm tails are still only protected by the 100A main incoming fuse which is beyond the rated current they would carry ?

 

[bigspark17]

Does the garage have any extraneous conductive parts.? Could you not run a 10mm t&e from db and put a small adaptable box somewhere appropriate. Diolch, cymru am byth .

 

[Llewelr]

Does the garage have any extraneous conductive parts.? Could you not run a 10mm t&e from db and put a small adaptable box somewhere appropriate. Diolch, cymru am byth .

Only if you class the garage door as an extraneous part haha , it's quite a large single garage and they've partitioned it so 3/4 of it is going to be office space and the rest is going to house the consumer unit and be for general storage and access to the roof space.

Im not concerned with the install in the garage as such, it's the feed from the meter to the garage and the fusing of the supply cable that concerns me.

 

[davesparks]

Its just your standard new build meter box service head, meter, isolator but once you add earth block and Henley block you don't have any more room to mount anything on the chipboard.

Uksparks mentioned putting an isolator switch in ? I could do that below the meter box but it doesn't protect the cable.

Yeah, absolutely no room to terminate SWA into a KMF in a standard meter box is there!

 

[Llewelr]

Yeah, absolutely no room to terminate SWA into a KMF in a standard meter box is there!

Not when there is a 100a isolator taking up the space where you've got your Henley block and KMF, No

 

[davesparks]

Not when there is a 100a isolator taking up the space where you've got your Henley block and KMF, No

Move it then

 

[davesparks]

All this does of course beg the question of why you have run a cable to a position where you already believe you cannot terminate it correctly? Why didn't you run it to somewhere more suitable such as the CU???


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[Llewelr]

All this does of course beg the question of why you have run a cable to a position where you already believe you cannot terminate it correctly? Why didn't you run it to somewhere more suitable such as the CU???


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CU Is in the downstairs toilet and completely unsuitable, would of meant making a phenomenal mess getting it there and that's one thing they wanted to avoid which brings us to this situation haha. Thanks for your input though I've got it sussed now

 

[davesparks]

CU Is in the downstairs toilet and completely unsuitable, would of meant making a phenomenal mess getting it there and that's one thing they wanted to avoid which brings us to this situation haha. Thanks for your input though I've got it sussed now

Care to share your solution to the problem so that others may learn from it?

 

[Llewelr]

Care to share your solution to the problem so that others may learn from it?

Going to put an adaptable box right below the meter box to terminate the armoured into, din rail with 40a double pole mcb and a din rail terminal for the earth, 10mm into the meter box, or in the adaptable box I could just put a KMF with a 45a fuse like you did.

 

[bigspark17]

Going to put an adaptable box right below the meter box to terminate the armoured into, din rail with 40a double pole mcb and a din rail terminal for the earth, 10mm into the meter box, or in the adaptable box I could just put a KMF with a 45a fuse like you did.

10mm tails into henley blocks.? What size is dno fuse, presuming 100A?!

 

[Llewelr]

10mm tails into henley blocks.? What size is dno fuse, presuming 100A?!

Fair comment, DNO Fuse is 100A so 25mm will be more suitable