How many fluorescent fixtures on a 15 amp circuit?

Notch1988 · Oct 9, 2012

I'm planning to use the 8 foot, 4 bulb T8 strip light fixtures. With 4x32W bulbs per fixture I'm looking at about 1.2 amps in bulbs alone. I'm wondering if 6 of these fixtures on one 15 amp circuit is too much or should I go with 4 per circuit. I'm doing 12 fixtures in total, so it's either 2 circuits or 3.

Steevo · Oct 9, 2012

Six of the 8 foot, 4 bulb T8 strip light fixtures should be no problem on a 15A circuit.
Check the ballast for actual amperage draw, not a cumulative multiplier of bulbs

Charles (in GA) · Oct 9, 2012

Code says you cannot exceed 80% of the capacity of a circuit for continuous loads. Lighting is defined as a continuous load (3 hrs or more is the def of continuous, but code also defines specific items as continuous, including lighting).

Thus you should not exceed 12 amps on a 15 amp circuit, or 16 amps on a 20 amp circuit. This would make 10 fixtures your max on a 15 amp circuit. If these fixtures have magnetic ballast, the induction loads are much higher, and I would not put this many fixtures on a circuit.

Indeed, use data plate specs for the calculations, not a 4 bulbs times 32 watts calculation.

Charles

Aceman · Oct 9, 2012

Every 4 lamp T8 ballast I've looked at draws between .99-1.00 amp at 120v. It's easy to check for yourself.

marty_p · Oct 9, 2012

Aceman said:
Every 4 lamp T8 ballast I've looked at draws between .99-1.00 amp at 120v. It's easy to check for yourself.

With 12 four-bulb fixtures, prepare for serious light!!!

Oh, and don't forget to post our sought-after pics later on... :thumbup:

eljefino · Oct 10, 2012

You can do a bunch on a circuit but check into what your 69 cent switches are rated for capacity. It's also cool to have a couple switches to "stagger" the startup and just have more control over things.

theoldwizard1 · Oct 10, 2012

I know Square D sells special breaker just for fluorescent and HID loads (QO115HID).

Ferrino · Oct 10, 2012

Can I please ask which fixtures you went for? I'm in the same position of adding T8 lighting to my garage...

Falcon67 · Oct 10, 2012

I used 1A / fixture as my mark. One 20A light run has 8 fixtures (T8 4 bulb) and the other has 5, so the wires are loafin'.

This is what i used: http://www.homedepot.com/h_d1/N-5yc...3&langId=-1&keyword=lithonia+t8&storeId=10051

Notch1988 · Oct 10, 2012

Falcon67 said:
I used 1A / fixture as my mark. One 20A light run has 8 fixtures (T8 4 bulb) and the other has 5, so the wires are loafin'.

This is what i used: http://www.homedepot.com/h_d1/N-5yc...3&langId=-1&keyword=lithonia+t8&storeId=10051

Are these fixtures rated for a 20 amp circuit?

Falcon67 · Oct 10, 2012

What do you mean "rated for a 20A circuit". It's a 12 gauge wire run on a 20A breaker, the lights don't care.

Notch1988 · Oct 11, 2012

Falcon67 said:
What do you mean "rated for a 20A circuit". It's a 12 gauge wire run on a 20A breaker, the lights don't care.

I just wired my basement and discovered that fixtures hard wired into a 20 amp circuit need to be rated for it. I had run a 20 amp circuit to the bathroom and put the lights and fan on it and got told it wasn't correct cuz the lights and fan weren't rated for a 20 amp circuit. I'm not sure how you find out if it is or isn't though.

Falcon67 · Oct 11, 2012

Must be a Canadian thing. You can put a 7 watt Christmas light on a 20A circuit if you want. The 20A is just the circuit capacity maximum. Wire size is specified for certain max capacity of a circuit. 14 ga wire is typically used for a 15A, 12 ga is considered good for 20A. Rules require that lighting circuits only be loaded to a certain percentage of the capability of the circuit as noted above. You can hang permanent connected lights, etc on there until you reach the 80% max figure. The actual current draw or load on the circuit is determined by the sum of the connected devices and not by the size of the breaker or wire size installed. If your connected device(s) exceed the 80% max, then you have to upsize the wire and breaker that supplies the device(s). If I was looking for a circuit rating, it would be some minimum requirement specified by the manufacturer or just the voltage requirement - 120V or 240V. Reviewing the spec sheet shows that the ballasts are rated for use on 120-277V power.

miner · Oct 12, 2012

The way I have heard it described is: take amperage times voltage to get wattage capacity (e.g., 15 amps * 120 volts = 1800 watts) then you can distribute this capacity to as many fixtures as you want so long as the sum total of the rated wattages of all fixtures does not exceed this amount. Multiply by .8 for continuous load derating. If your fixtures are rated at 130 watts max, that would be about 11 fixtures on a 15 amp circuit.

mrb · Oct 12, 2012

miner said:
The way I have heard it described is: take amperage times voltage to get wattage capacity (e.g., 15 amps * 120 volts = 1800 watts) then you can distribute this capacity to as many fixtures as you want so long as the sum total of the rated wattages of all fixtures does not exceed this amount. Multiply by .8 for continuous load derating. If your fixtures are rated at 130 watts max, that would be about 11 fixtures on a 15 amp circuit.

on fluorescent fixtures you have to use the amps listed on the ballast, not the wattage of the lamps.

Notch1988 · Oct 12, 2012

mrb said:
on fluorescent fixtures you have to use the amps listed on the ballast, not the wattage of the lamps.

Wouldn't it be both, or does the rating listed include the ballast and bulbs?

eljefino · Oct 12, 2012

Falcon67 said:
Must be a Canadian thing. You can put a 7 watt Christmas light on a 20A circuit if you want. The 20A is just the circuit capacity maximum. Wire size is specified for certain max capacity of a circuit.

Maybe canada is worried that the little pigtail coming from the fixture might melt down if the fixture itself goes berzerk and the hookup wire is too skinny for too big an incoming feed/breaker?

pattenp · Oct 12, 2012

Notch1988 said:
Wouldn't it be both, or does the rating listed include the ballast and bulbs?

Ballast have a label that shows what the amp draw is based on the number and type of tubes being used.

Falcon67 · Oct 13, 2012

eljefino said:
Maybe canada is worried that the little pigtail coming from the fixture might melt down if the fixture itself goes berzerk and the hookup wire is too skinny for too big an incoming feed/breaker?

Eh? Not following exactly

How many fluorescent fixtures on a 15 amp circuit?

Notch1988

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Steevo

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Charles (in GA)

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Aceman

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marty_p

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eljefino

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theoldwizard1

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Ferrino

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Falcon67

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Notch1988

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Falcon67

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Notch1988

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Falcon67

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miner

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mrb

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Notch1988

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