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 42 replies
  • Subscribers 31 subscribers
  • Views 6068 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

Number of luminaires on a lighting circuit – new house

Dave Stevenson

Hi,


I am doing a provisional lighting layout for a new house which will use LED lamps throughout. (The final electrical design will be done by the building contractor, but I want to get things right in the design brief  that I give him and want to make sure that I’m not giving him “guidelines” that are not possible to meet.)


The intent is that there will be separate circuits for the ground and first floors, but that additional circuits should not be required. As all of the luminaires will be using low power, mains voltage, LEDs, predominantly downlights, I don’t think there is any concern around exceeding the current capacity of the (1.0 or 1.5mm2) cable and a 6A RCD.


The only issue that I could see is the electrical designer raising is the guidelines in the 2018 On-Site guide in Appendix on Maximum Demand and Diversity. The Appendix is marked as “Guidance Only” but I am concerned that it would be easy for the contactor to just take compliance with it as the easy way out.


Table A1 gives the assumed current demand for a lighting circuit to be 100W per lighting outlet (I guess from when 100W incandescents were the norm), that would be around 12 luminaires or 18 allowing for the diversity in Table A2. (The section does say that “The values given in Table A2, therefore, may be increased or decreased as decided by the installation designer concerned.”)  With LED downlighters everywhere, there will be around 60 luminaires with a load around 300W. (One could take the view that a new owner could replace all the LEDs with 100W fittings, but I think that would be an unreasonable argument.)


Other than arguments around inconvenience should the circuit trip, would it be unreasonable to ask the designer to implement a singe circuit for these loads? (Assuming of course, that the voltage drop was within spec.)


As an aside, is there any reason that external lights could not be on the same RCD protected circuit as the rest of the floor?


Regards

Dave

 


Parents
  • 0
    davezawadi (David Stone):

    I know you are always very aware of fire Z, but this is ridiculous. You need to realise that LED power supplies are inherently fire resistant in several ways. The components used are very small, they are often the fastest fuses known to man, and cannot dissipate many watts without vapourising. To start a fire one needs significant power dissipation but this is close to impossible with these items, at perhaps 5W maximum, and if anything goes short circuit (which it almost certainly will) the current will trip the circuit OPD. 


     A 16 Amp M.C.B. needs many Amps  trip it off. Especially a C16 type on a short circuit. So, do L.E.D. luminaries have internal fuses or do they just rely upon their tiny electronic parts exploding to clear a fault? I don't really like the thought of that happening. I know that the old wound toroidal lighting transformers had an electrical fuse, and a thermal fuse embedded into the windings for safety.


    Years ago, even electric clock points has a cartridge fuse, normally 1 Amp rated, for an electric clock that posed little fire risk or overload risk. Also Friedland bell transformers had internal fusing to supply just E.L.V. door bells. 


    Z.


Reply
  • 0
    davezawadi (David Stone):

    I know you are always very aware of fire Z, but this is ridiculous. You need to realise that LED power supplies are inherently fire resistant in several ways. The components used are very small, they are often the fastest fuses known to man, and cannot dissipate many watts without vapourising. To start a fire one needs significant power dissipation but this is close to impossible with these items, at perhaps 5W maximum, and if anything goes short circuit (which it almost certainly will) the current will trip the circuit OPD. 


     A 16 Amp M.C.B. needs many Amps  trip it off. Especially a C16 type on a short circuit. So, do L.E.D. luminaries have internal fuses or do they just rely upon their tiny electronic parts exploding to clear a fault? I don't really like the thought of that happening. I know that the old wound toroidal lighting transformers had an electrical fuse, and a thermal fuse embedded into the windings for safety.


    Years ago, even electric clock points has a cartridge fuse, normally 1 Amp rated, for an electric clock that posed little fire risk or overload risk. Also Friedland bell transformers had internal fusing to supply just E.L.V. door bells. 


    Z.


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