Im hanging some new 8' t-12 dual fluo. lights in the garage and dont want to overload the circuit.
I dont know exactly how to phrase this, but what is the max wattage you could run on a 15 amp circuit, including lights and outlets?
Is there a standard formula?
The ballast on the lights say 120 volt 1.74 amps 60hertz.
Since it draws 1.74 amps does this mean the circuit can handle approx. 8 lamps ? (1.74x 8= 14amps)

You could, but I would back it down to 6 or 7 tops. Quite often what i have seen is the manufacturers will give the amperage of the lamps, but not include the small amount of amperage the ballast also consumes. You would be better off at like 7 max per 15 amp circuit.

By the way, being in Nebraska, unless you have a heated shop those lights aren't going to fire up real when it is cold unless they are HO's.

Jeff

By the way, being in Nebraska, unless you have a heated shop those lights aren't going to fire up real when it is cold unless they are HO's.

Jeff

They don't even fire up in Washington.:sad:

Thanks Jeff,
Yes they are HO's.
The garage is 2 car attached, temp never got below 26 Degree inside even when outside temp was below zero this winter, they still fired up at that temp.
I installed a 5000 watt electric heater and it can maintain the temp at 70, though its only used when Im working in the garage.

By code, you are only supposed use 80% of a breakers capacity. On a 15 amp breaker you can put 12 amps.
James

jfkheat has got it right. there is the issue of wire size on the excisting circuit,typically lighting circuits are 15amp (breaker size) 14 gauge wire, 12 amps max. if you have 12 gauge wire in the walls u can use a 20 amp breaker and get 16amps max. dont upsize the breaker to 20 unless u are shure there is 12 gauge in the wall........ be glad to answer any ac electical questions. superbee

yes to the above
only load a breaker to 80% of the stated value on front
15 amp breaker max 12 amps on #14 wire
20 amp breaker max 16 amps on #12 wire
The amps stated on ballast is total consumpsion of ballast to lite lamps as designed.
HOs are good just be sure that the ballast are 0* start type or they will take a long time to come up to full brightness

Thanks guys,
Old circuit is 15 amp 14-2 wire.
I ran two additional circuits to the garage also, one is a 20 amp 12-2 wire and a 15 amp 14-2 wire.
For what Ive got I'll be way under the 80%.
Thanks again

By code, you are only supposed use 80% of a breakers capacity. On a 15 amp breaker you can put 12 amps.
James

jfkheat has got it right. there is the issue of wire size on the excisting circuit,typically lighting circuits are 15amp (breaker size) 14 gauge wire, 12 amps max. if you have 12 gauge wire in the walls u can use a 20 amp breaker and get 16amps max. dont upsize the breaker to 20 unless u are shure there is 12 gauge in the wall........ be glad to answer any ac electical questions. superbee

yes to the above
only load a breaker to 80% of the stated value on front
15 amp breaker max 12 amps on #14 wire
20 amp breaker max 16 amps on #12 wire
The amps stated on ballast is total consumpsion of ballast to lite lamps as designed.
HOs are good just be sure that the ballast are 0* start type or they will take a long time to come up to full brightness

What article of the NEC says you can only load a lighting circuit to 80%?

I know article 210.21(b)(2) states 80% max, but that is for maximum cord and plug connected load to a recepticle. 310.15(B)(2) is for derating to 80% but romex wouldn't be 4-6 current carrying conductors in a single raceway either.

I hear others say this 80% rule, but nobody has ever been able to show me where. So do any of you guys know where to find this 80% rule?

Jeff

I haven't been able to find it in my code book yet, Ill look some more.

I haven't been able to find it in my code book yet, Ill look some more.

I can find it for certain applications, none of which would pertain here. I hear this so often, I am curious as to where it is in the NEC.

Jeff

210.20 (A)Overcurrent Protection (continous and non continuous loads)
found on ecmweb.com
A requirement in 210.20(A) of the 2002 NEC states “the rating of the overcurrent device shall not be less than the noncontinuous load plus 125% of the continuous load.” In other words, you shouldn't load the overcurrent device at more than 80% of the continuous load. An exception permits you to rate the overcurrent device for 100% of the noncontinuous and continuous load “where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100% of its rating.” A similar requirement appears in 215.3 for feeders. Consider the following differences between standard devices and those rated for 100%, and their application in equipment.

A 100% rated MCCB is intended for continuous operation at 100% of its marked rating in an enclosure. That means it will carry 100% of rated current without overheating or tripping when enclosed. UL-Listed, 100% rated MCCBs are marked “Suitable for continuous operation at 100% of rating only if used in _____.” The blank identifies the enclosure or equipment in which they may be used.

Standard MCCBs are neither rated 100% nor marked as indicated above. All MCCBs are tested to carry 100% of rated current continuously without overheating or tripping when connected with conductors sized for their current rating. However, that test is done in open air without an enclosure. When standard MCCBs are enclosed — and especially when they're group-mounted, as in a panelboard — they're applied at 80% of their rating. In temperature tests within panelboards, switchboards, circuit breaker enclosures, and similar equipment, MCCBs are loaded to 80% of their rating unless they're 100% rated.

This applies to lighting which is continous duty.
assemble = panel and all of it's breaker
as I understand it

Thanks Barry!!

You wouldn't believe how many times I looked right over that in my search for where it says it. I have read that section so many times and never even realized that is what I was actually reading. :clonk:

Jeff

15 amps x 120 volts = 1800 watts.
1800w x 80% = 1440 watts.

I always use the 80% factor and I always put the lights on more than one circuit. If something blows I don't want to be in the dark! I've got lights on 3 circuits in my garage. 2 for the fluorescent and one for incandescent for those quick trips just to grab a tool.