The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 114 replies
  • Subscribers 31 subscribers
  • Views 11489 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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
Parents
  • 0
    Okay, I think this question is daft, but let’s run with it.


    A 3 x 3 grid is probably not workable if the joists are at even centres as you will hit one or more of them on the crossing run, an even number of lights usually work better on that run.


    I will typically put three lines of lights on the narrow run, joists permitting and switch the outer runs together and the centre run separately. At home I have six lights on the two outer lines and two in the centre, staggered. This allows the lighting level to be adjusted without dimmers for energy efficiency.


    This complies with the Building Regulations that have been in force for the last five years, a sngle light switch should normally operate no more than six light fittings with a maximum load of 100 circuit Watts.


    So I would take the circuit feed into the light switch back box then run a radial our to each group of lights with the lights daisy chained, if there is a junction box make sure if can be pulled out through a down light hole.


    What possible reason could there be for installing a ring, “tree” or “star”?


    Andy 




Reply
  • 0
    Okay, I think this question is daft, but let’s run with it.


    A 3 x 3 grid is probably not workable if the joists are at even centres as you will hit one or more of them on the crossing run, an even number of lights usually work better on that run.


    I will typically put three lines of lights on the narrow run, joists permitting and switch the outer runs together and the centre run separately. At home I have six lights on the two outer lines and two in the centre, staggered. This allows the lighting level to be adjusted without dimmers for energy efficiency.


    This complies with the Building Regulations that have been in force for the last five years, a sngle light switch should normally operate no more than six light fittings with a maximum load of 100 circuit Watts.


    So I would take the circuit feed into the light switch back box then run a radial our to each group of lights with the lights daisy chained, if there is a junction box make sure if can be pulled out through a down light hole.


    What possible reason could there be for installing a ring, “tree” or “star”?


    Andy 




Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines