Illumination/Lighting branch circuit breaker calculation

[Frank A]

Hello.


I'm trying to calculate a bunch of illumination/lightning branch circuits. Reading some guides on the Internet, I came upon a part that says the amps value must be multiplied by 140%. Is that true?


And if so, which article says so?

 

[augie47]

Hello.


I'm trying to calculate a bunch of illumination/lightning branch circuits. Reading some guides on the Internet, I came upon a part that says the amps value must be multiplied by 140%. Is that true?


And if so, which article says so?

If you read it on the Internet it has to be true, correct ?
Might depend on the value you are using. A lighting load that operates 3 hours or more continuously would have to be calculated at 125% of the load.
If you are working with lamp watts from a fluorescent or HID or LED you have to take into account the losses in the ballast (driver) and 140% might not be that far off so it depends on the type lamp, hours of operation and the number you are using (lamp watts vs actual load).

 

[Dennis Alwon]

Usually for lighting loads on commercial applications the lights will be on 3 hours or more so they are continuous.

215.3 Overcurrent Protection. Feeders shall be protected
against overcurrent in accordance with the provisions of
Part I of Article 240. Where a feeder supplies continuous
loads or any combination of continuous and noncontinuous
loads, the rating of the overcurrent device shall not be less
than the noncontinuous load plus 125 percent of the continuous
load.

 

[Frank A]

If you read it on the Internet it has to be true, correct ?
Might depend on the value you are using. A lighting load that operates 3 hours or more continuously would have to be calculated at 125% of the load.
If you are working with lamp watts from a fluorescent or HID or LED you have to take into account the losses in the ballast (driver) and 140% might not be that far off so it depends on the type lamp, hours of operation and the number you are using (lamp watts vs actual load).

Haha.

That's right. I missed that. They're calculating the lighting branch circuit for HPS luminaires.

Could you show me exactly which NEC article corresponds with the 140% for ballast?

 

[JoeStillman]

220.16(B) Inductive and LED Lighting Loads. For circuits supplying lighting units that have ballasts, transformers, autotransformers, or LED drivers, the calculated load shall be based on the total ampere ratings of such units and not on the total watts of the lamps.

(From the 2014 NEC)

 

[Dennis Alwon]

Haha.

That's right. I missed that. They're calculating the lighting branch circuit for HPS luminaires.

Could you show me exactly which NEC article corresponds with the 140% for ballast?

I don't believe the nec states 140% but as stated above you need to use the ballast etc not the wattage. You may have a 4-32 watt trouffer-- that is not nec essarily 138 watts because the ballasts will draw a bit more than the actual wattage. The older ones I believe were about .8 amps per ballast. 2 x .8 = 1.6

1.6 * 120 = 192 watts

138 * 1.4 = 193 watts so 140% is close but you still use the ballast rating