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Recommended wiring topology for multiple lamps on one switch?

Nicholas Lee
As having an array of mains downlighters or spotlights in a ceiling is now fashionable, (rather than a single central luminaire), this begs the question of how to optimally and correctly wire them all up to the light switch.

In the case where one light switch operates multiple lights (as powered by from the domestic lighting circuit), there are several possible ways to wire from the switch to each of the lamps.

[It is taken as obvious that each lamp needs to be wired in parallel, with connections to the mains neutral and the switched-live wires.]


The (twin-and-earth) cable routing from the switch to all the lights and could be one of:

1) Daisy-chain   (the cable goes from the switch to one lamp, and then on to the next lamp, until all lamps are connected)

2) Ring    (like the daisy-chain wiring, but the final connection then links back to the switch to create a "ring main")

3) Star   (separate cables go from the switch to each lamp)

4) Tree   (i.e. a balanced spanning-tree, where the cable goes from the switch to two lamps, and each of them connect to two lamps, branching until all lamps are connected)

Each topology has different implications regarding the current distribution, and its associated heating losses in each segment of cable.

For example, a Daisy-chain topology has the highest current loading in the cable segment closest to the switch, but it uses the least cable; whereas the star topology has equal current loading in all its cable segments, but it uses the most cable.


Do the IET regulations recommend a particular wiring topology for particular scenarios, and what does everyone use in practice?

Thank you
  • 0
    Daisy chain - it's easiest and even with a score of 9W downlighters, it is difficult to see how they could overload anything.
  • 0
    Daisy chain - it's easiest and even with a score of 9W downlighters, it is difficult to see how they could overload anything.
  • 0
    Daisy chain - it's easiest and even with a score of 9W downlighters, it is difficult to see how they could overload anything.
  • 0

    Do the IET regulations recommend a particular wiring topology for particular scenarios, and what does everyone use in practice?




    1) No, though it should be laid out to allow maintenance and testing (so please avoid hidden joints if you can)

    2) As far as I can tell the preference seems to depend more on the building layout or personal foibles than any good electrical science.

    I'd not bother to ring unless there was some large CPC currents or a volt drop problem to think about, and this does not sound like either apply here. Radials, so either chain or tree structures or a mix of the same are common.


  • 0

    Do the IET regulations recommend a particular wiring topology for particular scenarios, and what does everyone use in practice?




    1) No, though it should be laid out to allow maintenance and testing (so please avoid hidden joints if you can)

    2) As far as I can tell the preference seems to depend more on the building layout or personal foibles than any good electrical science.

    I'd not bother to ring unless there was some large CPC currents or a volt drop problem to think about, and this does not sound like either apply here. Radials, so either chain or tree structures or a mix of the same are common.


  • 0

    Do the IET regulations recommend a particular wiring topology for particular scenarios, and what does everyone use in practice?




    1) No, though it should be laid out to allow maintenance and testing (so please avoid hidden joints if you can)

    2) As far as I can tell the preference seems to depend more on the building layout or personal foibles than any good electrical science.

    I'd not bother to ring unless there was some large CPC currents or a volt drop problem to think about, and this does not sound like either apply here. Radials, so either chain or tree structures or a mix of the same are common.


  • 0
    Indeed - usually it's strictly none of the above but some hybrid (e.g. a tree of several radials) - usually optimised by ease of cable runs (e.g. minimising the number of floor boards to be pulled up or joists drilled though) and restrictions on the number of cables that can comfortably be accommodated in each fitting.

      - Andy.
  • 0
    Indeed - usually it's strictly none of the above but some hybrid (e.g. a tree of several radials) - usually optimised by ease of cable runs (e.g. minimising the number of floor boards to be pulled up or joists drilled though) and restrictions on the number of cables that can comfortably be accommodated in each fitting.

      - Andy.
  • 0
    Indeed - usually it's strictly none of the above but some hybrid (e.g. a tree of several radials) - usually optimised by ease of cable runs (e.g. minimising the number of floor boards to be pulled up or joists drilled though) and restrictions on the number of cables that can comfortably be accommodated in each fitting.

      - Andy.
  • 0
    Let's take a 3 x 3 grid with joists running left to right.


    "tree": go up the right hand side - JB (MF of course) in the first space with its cables supplying the first three lamps to the left, and going onwards; drill through joist, another JB and supply the 4th to 6th lamps; drill through joist, supply 7th to 9th lamps.


    "daisy chain": start on the right hand side and supply lamps 1 - 3; drill through joist and supply 6th - 4th lamps; drill through joist, supply 7th to 9th lamps.


    One method uses two junction boxes, the other doesn't. However, I do accept, as Andy said, that it may not always be possible to lift boards as you would wish.

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