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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
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    A minimum spanning tree or minimum weight spanning tree is a subset of the edges of a connected, edge-weighted directed graph that connects all the vertices together, without any cycles and with the minimum possible total edge weight.

     





    I can't imagine many of the more domestic sparks I know chewing on a  pencil and describing  it that way, but if there is access from above that makes one layout easier than the other it will be done following the route of least aggro, using a similar level of native cunning to that required to work out where to aim next on the dartboard. And to me at least, tree and star structures are still legitimate examples of radial circuits, as well as the simple linear chain. Also you may feed any of these layouts from in the middle if there are lights to the left and right of the switch, indeed we have this in the scout hut, the switch by the main doors turns on lights to both right and left of the one in front of the door, as the corridor runs both ways, so you may think its two trees, or at least 2 'Y' shapes one trunk going down each corridor to supply 3 lights, and splitting as a Y because the corridor has a wider stub at the location of the fire exits.
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    A minimum spanning tree or minimum weight spanning tree is a subset of the edges of a connected, edge-weighted directed graph that connects all the vertices together, without any cycles and with the minimum possible total edge weight.

     





    I can't imagine many of the more domestic sparks I know chewing on a  pencil and describing  it that way, but if there is access from above that makes one layout easier than the other it will be done following the route of least aggro, using a similar level of native cunning to that required to work out where to aim next on the dartboard. And to me at least, tree and star structures are still legitimate examples of radial circuits, as well as the simple linear chain. Also you may feed any of these layouts from in the middle if there are lights to the left and right of the switch, indeed we have this in the scout hut, the switch by the main doors turns on lights to both right and left of the one in front of the door, as the corridor runs both ways, so you may think its two trees, or at least 2 'Y' shapes one trunk going down each corridor to supply 3 lights, and splitting as a Y because the corridor has a wider stub at the location of the fire exits.
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