lighting

I'm installing some recessed lighting. I'm using 12/2 cable on a 20amp breaker. The lighting will be 65watt floods. What's the maximum number of cans I can put on the same circuit? Thanks in advance.

 

27

 

John,
Thanks for the response. Where does 27 come from? My plan is to have 10 cans on the circuit. Can I and a pool table light to this circuit without overloading it?

 

I took 20 amps, multiplied it by 120 volts, to get 2400 watts. Then I took 80% of that, which provides a safety factor, and got 1920 watts. Then I divided 1920 watts by the 65 watts you plan for each bulb. That got me 27.5, and I rounded down to 27.

Ten lamps times 65 watts is 650 watts. That leaves you 1270 watts for your pool table lamp -- unless you're growing weed on your pool table, that's more than enough.

All of these calculations assume of course that you have no receptacles on this circuit, and nothing else either.

 

carefull with this. I believe that you must compute the branch circuit load according to art 220-3(b)(4) of the NEC 2002. you should base the load on the maximum rating of the allowed wattage for that fixture regardless of the lamp wattage you intend to use. I would say that is because someone else may put a higher wattage lamp in the socket than you are considering. typically for incandescant lighting this is often 150 watts even though the trim piece may have a lower rating. If it is flourescant you would use the rating on the fixture not the lamp wattage. after that you apply the 80% continuous load. in other words you cannot load a lighting circuit on a 20 amp branch breaker more than 16 amps. remember all the wiring components including the switches would need to be rated at 20 amps if you load it to its max, which is not a good installation.

 

With 1270 watts illuminating the pool table that would give you about 50 watts per square foot. So actually he could have the 10 recessed cans and still grow some pot on his pool table!

 

Whitey2 would be correct according to the NEC. It would be very important to make sure and get the appropriate 20A rated switches and/or dimmers for this branch. Most hardware stores have their big boxes of switches and recepts sitting out at 49-89 cents and they are rated for 15A...be careful with that.

JJRICK

 

Article 220 is for load calculations, not circuit design. Article 220 is not meant to apply to the design of an individual residential circuit.

I know of no NEC article that requires you to design a circuit for the maximum allowable fixture wattage.

15 amp switches are allowed on 20 amp circuits, unless a single switch is switching more than 15 amps.