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Multi-way domestic switch fuse: does anybody make one?

Chris Pearson
Scenario is intake in a store room: the other part of the building, which forms the front boundary of the plot, is the garage.


25 mm2 SWA supplies the house, which is at the back of the plot, and the intention is to protect it with an 80 A switch fuse in the hope that it will provide a measure of discrimination should a fault occur in the house (max 32 A MCB). Clearly there is plenty of choice here.


One option for supplying the garage is to put its CU adjacent to the intake and connect the tails to it (via Henley blocks) but Sir would prefer to have it in the garage itself. The distance back to the intake is unlikely to be less than 3 m, which rules out the possibility of putting the tails through the internal wall.


So if the CU is to be in a separate room, it seems that a second switch fuse is required. It would be so much neater if there could be one device with one switch and two (or more) fuses. I cannot find one, but does such a beast exist please?
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    Chris


    I think splitting the tails with a Henley block and a second switch fuse would be the simplest option. The other option would be a small distribution board with 2 fuses or circuit breakers to supply the different consumer units.
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    why can house and garage not share the one big fuse? It will never blow unless there is a dead short in the bit that would have been split tails otherwise.

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    I had a similar problem at home - intake in the cellar so wanted two submains - on to the main CU upstairs in the house and another out to the garage (and room for a 3rd if I ever got a workshop). Couldn't find anything ready-built so ended up putting 50x22 DIN rail fuse carriers in a box along with some terminals and isolator and a bit of bus-bar. Not entirely to the letter of the regs but the council electrician didn't even blink about it for the part-P inspection.


    Another possibility might be a 3-phase switchfuse - but using a single-phasing kit to put all three fuses on the same phase - but last time I looked down that road it was going to be rather an expensive approach (and you'd have to be careful to make sure the N wasn't overloaded - e.g. use a 100A rated unit even though you might only want 63A or 80A fuses.


    But otherwise, I agree it's a messy solution of henley blocks and several single-way switchfuses.


      - Andy.
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    mapj1:

    why can house and garage not share the one big fuse? It will never blow unless there is a dead short in the bit that would have been split tails otherwise.




    'Cos (1) that would require a JB downstream of the fuse, which wouldn't be easy to fit, so may as well have two switch fuses; and (2) the branch line would have to be 16 mm2 which would be overkill.

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    AJJewsbury:

    Another possibility might be a 3-phase switchfuse - but using a single-phasing kit to put all three fuses on the same phase - but last time I looked down that road it was going to be rather an expensive approach ...




    Sir has deeper pockets and shorter arms than a Yorkshireman.


    Yes. My first thought was that you would need a TPSN switch fuse (462.1.201) although in fact a TPN would do 'cos it would be possible to use two fuses for the lines and put in a solid link for the neutral.


    I think that Sir is going to have to lump it and have the CU in his shed, but thank you all for the comments - I thought that it was worth asking.

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    Cos

    (1) that would require a JB downstream of the fuse, which wouldn't be easy to fit, so may as well have two switch fuses; and

    (2) the branch line would have to be 16 mm2 which would be overkill.


    1) So you cannot fit two cables to one switch fuse ? Or an   adaptable box  and some line taps?

    2) is the max demand in the garage so high you'd need the full fat cable size - if only 32A breaker and 6A lights, then some 6mm would do  so long  as S/c protection is OK.



     

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    Sir has deeper pockets and shorter arms than a Yorkshireman.



    Quite possibly! My research at the time found things like this: https://www.tlc-direct.co.uk/Products/HGJFE310U.html which I still see as expensive - although there do seem to be cheaper versions available now I see.


      - Andy.
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    Speaking as a Yorkshireman by birth, but living the decadent south, I can concur on the short arms thing. Nowt wasted.
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    mapj1:






    Cos

    (1) that would require a JB downstream of the fuse, which wouldn't be easy to fit, so may as well have two switch fuses; and

    (2) the branch line would have to be 16 mm2 which would be overkill.


    1) So you cannot fit two cables to one switch fuse ? Or an   adaptable box  and some line taps?

    2) is the max demand in the garage so high you'd need the full fat cable size - if only 32A breaker and 6A lights, then some 6mm would do  so long  as S/c protection is OK.




    I fear that I must defer to Mike's wisdom. I had forgotten that the sum of the final circuits means that there would be no overload of a smaller cable to the garage.


    The length of the cable is so short that a s/c at the downstream end would still allow ADS to function.


    All that said, if it were my house, I would make provision for 32 A worth of EVCP.

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