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Thread: Ring and radial circuits

  1. #1
    Automated Home Legend Paul_B's Avatar
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    Default Ring and radial circuits

    First off I know that most of what I am discussing here falls under Part P regulations and as such needs to be done or approved by a qualified electrician. I'm just trying to improve my understanding to make sure I can speak with an electrician and know what is and isn't possible.

    In the UK most houses will use ring mains apart from the radial connection to the cooker and maybe an electric shower. It is also my understanding that you can spur from the ring using a fused connection, but this must only have one connection. You can spur as many times as you have sockets on the ring but each spur is limited to one device, i.e. you can't spur from a spur.

    So I'm guessing that if I wanted to add a radial circuit this would mean a new circuit from the main consumer unit?

    The reason for asking the above is I'm considering the use of an Idratek QRH-001 (DIN mounted and looks similar to the QRI-002
    although I might need 2 per room to control all sockets.

    MT

    Paul

  2. #2
    Automated Home Lurker
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    Not an electrician here either, but I have had a couple of major electrical works done of a similar nature.

    From previous experience there are 2 options. The first is to run a separate cable for each radial back to the main consumer unit. The second is to run a single cable of suitable size from the main unit to near your Idratek controller, put in a smaller sub-consumer unit and put radials in from there - in the same way garage consumer units work.

    I think it would all depend on how easy the cable routes are, and the intended load on each circuit to what would be best.

  3. #3
    Automated Home Legend Paul_B's Avatar
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    Thanks for responding tolley01. I was thinking exactly the same as your second option. Now to find a friendly electrician that will let me do most of the work but sign-off part-P

  4. #4
    Automated Home Jr Member
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    Hi Paul, As a sparks by trade I agree with most of the above - In the UK we use mostly ring final circuits - both ends of cable terminate in consumer unit, this provides dual paths for the current to flow - although it always chooses the path of least resistance. Our continental friends prefer radial circuits - which are easier to install, easier to fault find, but have lower current ratings. The issue with radial circuits is that the cumulative current of connected devices flows through a single cable - worst rating is the cable from the consumer unit to the first device. At a potential of 26A per double outlet on a normal 2.5mm T&E cable you are very near the max operating parameters of the cable if used on a radial circuit, hence the use of 13A fused connection plates and why 2.5mm radial circuits fed from a consumer unit should use an mcb of 16 or 20A, 4mm etc would have higher ratings.
    I hope you get an electrician to do the work, as any electrician that belongs to a professional body should NOT certify work they haven't installed themselves :-
    1. They have no idea how you installed the cables - jointed using selotape under the floor ??
    2. The certificates issued are legal documents and can be used in a court of law should anything go wrong - electricution, fire etc. And it would be the electrician that goes to jail if proved negligent.
    Regards, Paul.

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