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Thoughts on replacing switched fuse with small consumer unit

Alan B

I need to take a garage feed from the meter box in the picture below to enable installation of an EV charger. as consume unit is in the middle of the house and far from easy to get a cable in to it.

My initial plan has been to use an external IP rated consumer unit connected by henley blocks to the output of the main isolator.

Then I have been thinking that looking at the real estate taken by the current switched fuse (protecting cable run through house) and the Henley block I need it's basically the same size as a small garage consumer unit, probably more untidy. 

I know the DNO's frown on consumer units in the meter cupboard but given the switched fuse and henley blocks would have to be there anyway and I think there is a reasonable argument for a small consumer unit being a neater and in some ways more space efficient solution.

I would mount the new CU on spacers so that the meter tails could run underneath to the isolator above and maybe move the isolator up a bit, SWA garage feed would come up from the bottom.

The alternative would be to move the isolator up, squeeze a Henley block between it and the switched fuse.

Does this sound like  reasonable engineering judgement, anything I am missing?

Thanks

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  • 0

    What's the current fuse rated at? 60A 80A 100A? I suspect you'll struggle to find an MCB for a CU that'll match that - I don't think I've ever seen anything above 50A in a CU. Larger MCBs are available, but I suspect are intended for larger DBs rather than domestic CUs - you'd have to check with the appropriate manufacturer.

    +1 for the issue of reducing discrimination by using an MCB upstream of MCBs/RCBOs - it would be a shame to arrange things such that a single fault could black out the entire main house, where the chances of that happening were much less likely before.

    I do agree that a single enclosure would be a much neater solution - but would prefer HBC fuses to MCBs. Unfortunately there aren't many consumer unit manufacturers that support that approach (that was one of the issues I attempted to address in the fictional "Concept" CU range). I did resort to putting a couple of DIN-rail mounted 22x58 fuse carriers, some chunky terminals and an isolator in an enclosure to solve a similar problem in my home, but with now BS 7671 insisting that doing so means that the installer takes all the responsibilities of a manufacturer under BS EN 61439 makes that approach much more of a challenge these days).

     Guess the "proper" solution would be to introduce a 2nd enclosed space right next to the exiting meter box (another meter box is often used) and stick a set of Henleys and switchfuses in there.

       - Andy.

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  • 0

    What's the current fuse rated at? 60A 80A 100A? I suspect you'll struggle to find an MCB for a CU that'll match that - I don't think I've ever seen anything above 50A in a CU. Larger MCBs are available, but I suspect are intended for larger DBs rather than domestic CUs - you'd have to check with the appropriate manufacturer.

    +1 for the issue of reducing discrimination by using an MCB upstream of MCBs/RCBOs - it would be a shame to arrange things such that a single fault could black out the entire main house, where the chances of that happening were much less likely before.

    I do agree that a single enclosure would be a much neater solution - but would prefer HBC fuses to MCBs. Unfortunately there aren't many consumer unit manufacturers that support that approach (that was one of the issues I attempted to address in the fictional "Concept" CU range). I did resort to putting a couple of DIN-rail mounted 22x58 fuse carriers, some chunky terminals and an isolator in an enclosure to solve a similar problem in my home, but with now BS 7671 insisting that doing so means that the installer takes all the responsibilities of a manufacturer under BS EN 61439 makes that approach much more of a challenge these days).

     Guess the "proper" solution would be to introduce a 2nd enclosed space right next to the exiting meter box (another meter box is often used) and stick a set of Henleys and switchfuses in there.

       - Andy.

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  • 0 in reply to AJJewsbury
    AJJewsbury said:
     Guess the "proper" solution would be to introduce a 2nd enclosed space right next to the exiting meter box (another meter box is often used) and stick a set of Henleys and switchfuses in there.

    I agree, but it does appear that the meter box might be inset into the wall rather than surface-mounted. If not, definitely a second enclosure.

    For me, it is tails to a second enclosure, henley blocks and and new switch-fuse installed there, and the existing one moved across.

    (If that isn't a smart meter, the supplier might have a job squeezing one in.)

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