ECN Forum Forums Code Related Discussion NEC & other Code issues How many lights per circuit?

I forgot to mention a few things

1: There is an article in the NEC that requires fixtures that have interchangable lamps [in this instance - Incandescent lamps that have higher wattage ratings] to be rated at a minimum value. In your case, I think it's either 150 watts, or maybe it's higher, like Bill stated - 180 watts [I know 180 VA is the general purpose receptacle rating for commercial load calcs! but it might also apply to recessed fixtures]. I don't do that much work with non-fixed lighting [like the recess cans you're installing], but the few I have done in the past, I rated each one at 150 VA [or watts] per fixture.

You should design the lighting circuit to handle any future increase to the fixed outlets, which would be the result of someone changing out the 65 watt lamps for 100 watt lamps in the future. Since the largest Medium base Incandescent Lamp that is readilly available to the public is 150 watts, that would be the minimum you should rate each fixture at [the Incandescent fixtures, that is]. If there is any other manufacture's listings, follow that, but don't go below 150 watts per fixture.

2: If these lights will be on for 3 hours, or more, than the branch circuit needs to be LCL derated.
This means that the maximum ampacity of the branch circuit is reduced by 80% when the load continues for 3 hours or more.
Example: 15 amp circuit, maximum ampacity that can run for 3 hours or more = 12.5 amps [15x0.8]. This is an LCL derating [Long Continuous Loads].

Best if you do not max out your circuits, even if there is no LCL involved, just to keep the conductors cooler. Better to use #12 cu on the home runs [even in the outlets], but not totally needed [my own preferences ] and protect it with a 15 amp breaker.

Even doing this will cover the LCL derating situation

Just wanted to add these few things. Anyone that is more into the Residential angle should comment on these points beforehand [I do so little Residential work, that I am inclined to use Commercial calcs on stuff]. This lighting circuit might not require as much load calculation as I am figuring - rating the entire circuit by the minimum amperes of total connected fixtures. In my case, I would limit the number of fixtures per circuit to 10. This would be a total of 1500 VA [watts is OK], and includes an LCL derating, making the circuit's maximum current 12.5 amps.

Check other's comments first, then consider my calculations.

Scott SET