3 phase temp supply ?

Hi guys, iv been doing loads of basic new build single phase.

The next one is going to be 3 phase and a bigger house. I will treat as normal apart from adding a 3 phase board and balancing on the phases.

The owner has asked me to set up a temp supply. Can I do this but setting up say a garage board and couple of sockets, but using just one phase and not connecting the other two in, obviously neutral and earth will be connected. Thank you for any help

  • I am not clear what you are proposing. Will it be something like a construction site installation?

    There will have to be a service head and a meter. Yes, you could get a supplier to fit a SP meter and then fit a small CU. If you fit TP from the outset, you will need a TP board, but of course you would be perfectly free to install just the one socket circuit.

  • No problem just utilizing one of the three phases for the temp supply (provided of course the builders don't have any equipment that needs 3-phase).

    For a builder's supply, you might want to consider not using the supplier's earth but going TT instead - just because you'll almost certainly not be able to bond things properly on a building site which can increase some of the dangers with PME.

       - Andy.

  • If the 3 phase meter is installed then you could do worse than fit one of these 4 pole isos beside it,


    and then take L1 and N on some meter tail to any old single phase box with an RCD incomer feeding a board full of sockets. The switch stays and makes it easier to hook up and test the final 3ph board later.

    I have used  a wooden trestle in the past (yes this sort of thing, really that crude ) with plywood board on it with a DIN box RCD and a couple of breakers on one side, and about 8 double sockets on the other   If the decorators are in as well, it can be waterproofed with a bin bag or two, This is for when all the walls are being plastered, and there was no wish to leave a funny patch where the temp board was. I have even been known to screw it to the floorboards for the duration,,,

    The RCD means it is not so serious if the earthing is a bit hit and miss.


  • Thanks guys that was exactly what I needed. It will just be in one of the houses , il set a temp board as u suggest with a single phase board and sockets, just come off L1 and N

  • and balancing on the phases.

    Check with the DNO -  some (WPD?) I've heard prefer people to put the normal single phase loads all on the same phase (L1 say) and use the other two only for 3-phase loads (e.g. heat pumps and EV charge points). The idea being that they'll then balance things by rotating the phases for each house connection to the main - and can get a better overall balance that way than if say a whole estate is done with all the cookers on L1, showers on L2 and sockets on L3 or similar not entirely random pattern made up by electricians.

       - Andy.

  • Some MOPs will fit these free as part of the meter fitting.  E.on comes to mind but I guess there will be others.

  • In my case it was a devil of a job to get the MOP NOT to install the REC4 isolator. However, Mike's solution seems ideal.

  •  A TT earthing sytem would be needed for builders temp as per reg 704.411.3.1