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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.

  • 0

    I guess the first question is what are you supplying in the garage? Is it going to be a 3 phase distribution board?

    There’s a couple of ways you could do it but yes a 3 phase switch fuse would be a good way. I’ve used the 100a version of the unit you link to and I would say it was “ok”. Not as nicely designed or nice to install maybe as other brands but as you say it is significantly cheaper and perfectly adequate. I’m pretty sure the dimensions do include the handle so should fit into your space. 

  • 0 in reply to Sparkymark

    Hi,

    Thank you for getting back. In the garage a few things will be powered.

    1) A lathe and/or a milling machine. I don't have either at the minute, but typically these  have 3-phase motors, so that's why I want to get a 3-phase supply in the garage.

    2) Some single phase items - lighting, air-conditioning, 13 A sockets, and a 7.2 kW water heater, used to wash hands. That will only every run for a few minutes at a time.

    Although this is a garage, I have made a small section into a laboratory. That bit is air-conditioned. I forget what the maximum power that can draw is, but I don't think it is any more than 3 kW, and probably not more than 2 kW.

    So in essences, there will be one or two 3-phase items, and the rest will be single-phase.

    Since you say the Axiom range is perfectly adequate, that will be good enough for me. I will get an electrician to do this, but I want to have some idea of what the cost of the parts are. If he says the idolator is £300, I can reasonably say that one can be obtained for a lot less.

    I noticed a Hager 63 A fused isolator. The depth was given, and that would have been okay, but then it said something like "plus 70 mm for the handle". That would have made it too big. That's why I was concerned about the size. I found a data sheet on the Axiom one, but it was not exactly very informative. I have seen better data sheets.

    Dave

  • 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.

  • 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.

  • 0

    more likely to re-route the those tails to something else, which could just be a couple of "henley blocks" (example) to split them. Or routed to the to the side into to a 3 phase isolator  (some suppliers fit something like this) popular if further changes are expected as it  saves calling out for a DNO fuse pull each time to turn it off for an hour or whatever.)
    If the SWA falls badly short then an adaptable box with line taps in it or din rail and din terminals to make a  3 phase junction box is likely

    Mike

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