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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
    Modern L.E.D. lights often cause a large current surge (inrush current)  when first turned on. This has to be considered.


    Outside lights connected to internal lighting circuits could potentially cause trouble after a year or two. Outside lights are the ones that have to tolerate extremes of temperature, rain, wind and snow. If they become faulty and they trip off a protective device, then that can cause inconvenience. They can be a nuisance when fault finding after you have spent ages looking for an internal fault.


    Lighting does not have to lower and upper lighting circuits. The lighting could be divided to left side of house and right side of house to allow lights to work if one circuit fails, thus allowing some light to each floor.


    I used to supply a ground floor light near to the ground floor consumer unit on the upper floor circuit so that the user could change a fuse or reset a breaker with some helpful light.


    If outside lights are on their own independent dedicated circuit then villains or vandals that damage the outside lights will not trip off the inside lights as well. So safety and security are maintained.


    Z.
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  • 0
    Modern L.E.D. lights often cause a large current surge (inrush current)  when first turned on. This has to be considered.


    Outside lights connected to internal lighting circuits could potentially cause trouble after a year or two. Outside lights are the ones that have to tolerate extremes of temperature, rain, wind and snow. If they become faulty and they trip off a protective device, then that can cause inconvenience. They can be a nuisance when fault finding after you have spent ages looking for an internal fault.


    Lighting does not have to lower and upper lighting circuits. The lighting could be divided to left side of house and right side of house to allow lights to work if one circuit fails, thus allowing some light to each floor.


    I used to supply a ground floor light near to the ground floor consumer unit on the upper floor circuit so that the user could change a fuse or reset a breaker with some helpful light.


    If outside lights are on their own independent dedicated circuit then villains or vandals that damage the outside lights will not trip off the inside lights as well. So safety and security are maintained.


    Z.
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