Sizing the feed for a lighting circuit.

[John Gustafson]

How does the code address permanently installed sighting circuits? Do you supply for the rated maximum of the fixtures or to the load you are going to install?

I'm installing 32 recessed can lights in the 16' x 42' "attic" over the shop. The cans are rated for 75 watt incandescent bulbs. If you use the 75 watt value You need a feed capable of supplying about 3000 watts.

My plan is to utilize LED lamps. Load is about 13.5 watts per lamp. That drops the calculated load down to aboy 500 watts. 3000 watts at a minimum requires 2 15 amp branch circuits, more likely splitting the load between a 15 amp and a 20 amp circuit.

500 watts and thatch well within the capability of the 15 amp circuit that's already there for the stair lights.

My thoughts are that within the next 5 years or so you won't be able to buy incandescent 75W bulbs. Hard enough to find now as it is. Not going to worry about me, I know I won't put any thing but LED's in there and the first set will probably be the last set I'll ever have to concern myself with.

[Grant Aldridge]

Not positive on the code question but you should use the fixture rating. 32 can lights is a lot and they should be split info multiple circuits. Have you considered using dedicated led fixtures instead?

[Jason Roehl]

I think there's something about only having 10 boxes (in this case that would be fixtures) on a circuit.

[Greg R Bradley]

NEC does not specify maximum number of fixtures on a circuit. 10 is a reasonable practical limit if you are running your wiring to the first fixture, then to the second, etc. so you can just adjust the way you run your wiring.
You can use 80% of the circuit rating for a continuous load so 12amps on a 15a breaker and 16amps on a 20a breaker.
The problem comes that this is based upon the rating of the fixture, which seems to be 75watts. So it will NOT pass inspection on one circuit unless you install low power LED can lights.

[Paul F Franklin]

This is one of those things that probably comes down to your local AHJ, but in my case, the retrofit LED trims came with stickers that said something like, this fixture has been modified to use LED lamp and cannot be used with incandescent lamps. (even though the modification involved screwing in the light bulb base shaped adapter from the LED trim.

I have 20-22 fixtures on a single 15 amp circuit. Inspector has no issue.

This is not a safety issue. If someone went back and plugged in incan bulbs, the breaker would blow.

[Peter Christensen]

Unless you have already paid for the can lights I would go directly to the LED fixture because insulation can be placed directly on top whereas the pot lights you mentioned have to have space around them in case someone were to put incandescents back in the fixture. You don't loose the insulation value with the 1" thickness of the LED fixture and it is easier to seal the vapour barrier too. The ones we have in the house are 12 watts and draw .2 amps at maximum each. Your 32 lights would draw 6.4 amps total. If you are still planning look into buying direct from the makers in China through Alibaba or AliExpress.

[Ken Fitzgerald]

Talk with your local electrical inspector. When I built my shop, I got a lot of good information I used in the planning and executing stages. The inspector can be a wealth of information.

[John Gustafson]

Petr, I had considered something along those lines, Not AliBaba per se but was looking for a Desigbed LED fixture. I was looking though at "New Work fixtures". Ones that could be installed without a finished ceiling. That sequence gave me lights to work on finishing the room. You made me rethink that sequence. The prewireing could be done ahead of the ceiling install. Then the ceiling and go with retrofit LED units. Get it all in place and blow insulation in afterwards. Pricewise the higher cost of the fixtures is almost covered by going to 14 gauge hookup and getting rid of the new 20 amp feeds from the panel. Only issue is putting up the ceiling earlier than I had planned but then it goes up easier since don't have to match cutouts to fit the installed lights.
I can do this with Home Depot hardware but I do want to look at the alibaba idea. . Thanks for triggering a rethink of this whole process.