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3-phase supply to a garage from a house

David Kirkby

I've got a 3-phase (4-wire) supplied to my house, and are looking to get the 3-phase supply to the garage. The supply is fed via 3 x 60 A fuses.  I assume a 3-phase isolator with internal fuses is a typical way to do this. 

I was looking at the Axiom range, in particular the SF63

https://www.cedelectrical.co.uk/pdf/axiom_industrial.pdf

These seem significantly cheaper than similar units from Hager and elsewhere, and I was wondering what the quality is like. Since it is going to be located in  the house, supplying power to the garage, it is not going to get much use, like in an industrial location. It will probably only get switched once per year or so on average.

Is it acceptable to have the switch in one box, and isolator in the other, rather than both in the one box? Having these separate might be preferable, as I assume the depth will be less.  I have only 167 mm between the mounting surface and a sliding cupboard. It's not clear from the above data sheet if the 141 mm includes the handle or not. If so, that would fit, but if not, the handle will probably prevent the cupboard being closed.  In which case, I assume a switch in one box and fuses in another would probably allow for a smaller overall depth, but maybe I am mistaken on that. (On that particular range, the boxes are the same sizes, irrespective of whether there are fuses or not in there.

Currently the garage has a single-phase supply, fused at 60 A, but there is a 4-core cable, as some of the cores were used to supply economy 7 heating, although that's not being used any more. The conductors are 16 mm^2.

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    In some designs there is more giblets to remove to drill cable entry holes and then things are a bit finicky to put back together, the nicer ones have removable side plates that you unscrew, drill and re-fit.  Allow bend radii and jiggle  room for cables to be terminated, 16mm can be quite willful and at one end or the other the position of the terminals  will be fighting the cable's natural lay direction . If need be the cable can be glanded / Pirahna'd off to an adaptable box and then the single cores brought the last few inches into the switch gear in trunking or similar. In the past I have sunk such things partly into the wall so that the lid joint is more or less plaster flush. It does not say you can in the instructions, - but it does not say don't either.
    A respectable sparks will want to check the existing cable for insulation faults and visually inspect as much as possible before adopting it. If the existing cable is long the Zs and clearing time, or volt drops, may set the maximum fuse, rather than the thermal current rating.
    They are more likely to produce the job you want, if you do as much of the prep as possible so that is the route of least effort - at this point  I'd normally ask how you feel about digging your own trenches, but that is not relevant here, but drawing on the wall where you'd prefer things to go, where holes are and pipes to avoid  and so on is not a bad idea.

    I presume the switch in one box, and isolator in the other is a typo and 'fuses' was intended !?  If so that's fine, but only if it is worth it - many designs are the same depth anyway.

    Mike.

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  • 0

    In some designs there is more giblets to remove to drill cable entry holes and then things are a bit finicky to put back together, the nicer ones have removable side plates that you unscrew, drill and re-fit.  Allow bend radii and jiggle  room for cables to be terminated, 16mm can be quite willful and at one end or the other the position of the terminals  will be fighting the cable's natural lay direction . If need be the cable can be glanded / Pirahna'd off to an adaptable box and then the single cores brought the last few inches into the switch gear in trunking or similar. In the past I have sunk such things partly into the wall so that the lid joint is more or less plaster flush. It does not say you can in the instructions, - but it does not say don't either.
    A respectable sparks will want to check the existing cable for insulation faults and visually inspect as much as possible before adopting it. If the existing cable is long the Zs and clearing time, or volt drops, may set the maximum fuse, rather than the thermal current rating.
    They are more likely to produce the job you want, if you do as much of the prep as possible so that is the route of least effort - at this point  I'd normally ask how you feel about digging your own trenches, but that is not relevant here, but drawing on the wall where you'd prefer things to go, where holes are and pipes to avoid  and so on is not a bad idea.

    I presume the switch in one box, and isolator in the other is a typo and 'fuses' was intended !?  If so that's fine, but only if it is worth it - many designs are the same depth anyway.

    Mike.

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  • 0 in reply to mapj1

    Thank you. Yes, the isolator in one box and the switch in another were a typo. I did mean the fuses in the 2nd box.

    If the depth of the SF63 here

    https://www.cedelectrical.co.uk/pdf/axiom_industrial.pdf

    includes the handle, then that will fit without a problem. A similar 63 A unit from Hager would have been unsuitable.

    I don't know where the spark will pick up the three phases from. There's probably about 1.5 m between the end of the 16 mm^2 cable to the garage, and semi-convenient places to pick up the phases from. I don't know where he/she would pick them up from, as two go directly between the meter and a 3-phase contactor for the economy 7. The contactor has about a dozen entry/exit holes for cables. My guess is that the multiple bits of that are in parallel, and wiring two of the phases to the contactor might be easiest. There's not a lot of space between the meter and contactor - probably 200 mm or so.

    I would attach a photo, but my laptop battery is nearly flat, are we have a 6-hour power outage today - we received notification of this a couple of weeks ago.

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