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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
    Hmm ,

    last item I wonder why they say "normally" and what is a "circuit watt" as opposed to a "watt".

    I can`t think of a reason.

    Seems if I put 8 x 50W lamps on one switch in say a kitchen then it contravenes the building regs or maybe just the guidance to them.
  • 0
    Hmm ,

    last item I wonder why they say "normally" and what is a "circuit watt" as opposed to a "watt".

    I can`t think of a reason.

    Seems if I put 8 x 50W lamps on one switch in say a kitchen then it contravenes the building regs or maybe just the guidance to them.
  • 0
    Hmm ,

    last item I wonder why they say "normally" and what is a "circuit watt" as opposed to a "watt".

    I can`t think of a reason.

    Seems if I put 8 x 50W lamps on one switch in say a kitchen then it contravenes the building regs or maybe just the guidance to them.
  • 0
    it is a direct quote from
    Domestic Building Services Compliance Guide  which in turn is an explanation of the non statutory advice in


    The 4 versions of part L in the Approved documents  which in turn is supposed to be advice on meeting the  legally enforcable
    Building Regulations 2010. here


    The law says nothing about no. of fittings per switch, but requires simply that

    Reasonable provision shall be made for the conservation of fuel and power in buildings by:
    (a) limiting heat gains and losses–(i) through thermal elements and other parts of the building fabric; and(ii) from pipes, ducts and vessels used for space heating, space cooling and hot water services;
    (b) providing fixed building services which–(i) are energy efficient;(ii) have effective controls; and(iii) are commissioned by testing and adjusting as necessary to ensure they use no more fuel and power than is reasonable in the circumstance





    It is part of 'b'.

    (the approved doc does not mention light switches at all either)


    You could be forgiven for thinking that it has all become far too complex for what is really needed, and with complexity comes a great deal of scope for not doing it very well.

  • 0
    it is a direct quote from
    Domestic Building Services Compliance Guide  which in turn is an explanation of the non statutory advice in


    The 4 versions of part L in the Approved documents  which in turn is supposed to be advice on meeting the  legally enforcable
    Building Regulations 2010. here


    The law says nothing about no. of fittings per switch, but requires simply that

    Reasonable provision shall be made for the conservation of fuel and power in buildings by:
    (a) limiting heat gains and losses–(i) through thermal elements and other parts of the building fabric; and(ii) from pipes, ducts and vessels used for space heating, space cooling and hot water services;
    (b) providing fixed building services which–(i) are energy efficient;(ii) have effective controls; and(iii) are commissioned by testing and adjusting as necessary to ensure they use no more fuel and power than is reasonable in the circumstance





    It is part of 'b'.

    (the approved doc does not mention light switches at all either)


    You could be forgiven for thinking that it has all become far too complex for what is really needed, and with complexity comes a great deal of scope for not doing it very well.

  • 0
    it is a direct quote from
    Domestic Building Services Compliance Guide  which in turn is an explanation of the non statutory advice in


    The 4 versions of part L in the Approved documents  which in turn is supposed to be advice on meeting the  legally enforcable
    Building Regulations 2010. here


    The law says nothing about no. of fittings per switch, but requires simply that

    Reasonable provision shall be made for the conservation of fuel and power in buildings by:
    (a) limiting heat gains and losses–(i) through thermal elements and other parts of the building fabric; and(ii) from pipes, ducts and vessels used for space heating, space cooling and hot water services;
    (b) providing fixed building services which–(i) are energy efficient;(ii) have effective controls; and(iii) are commissioned by testing and adjusting as necessary to ensure they use no more fuel and power than is reasonable in the circumstance





    It is part of 'b'.

    (the approved doc does not mention light switches at all either)


    You could be forgiven for thinking that it has all become far too complex for what is really needed, and with complexity comes a great deal of scope for not doing it very well.

  • 0
    Mood lighting and ambience requires consideration as well.


    Andy
  • 0
    Mood lighting and ambience requires consideration as well.


    Andy
  • 0
    Mood lighting and ambience requires consideration as well.


    Andy
  • 0

    what is a "circuit watt" as opposed to a "watt"



    It's the power that flows in the supplying circuit, rather than just the lamp. E.g. an 18W fluorescent fitting might draw current equivalent to maybe 25W once you take account of control gear losses etc.

      - Andy.

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