LOAD CALCULATOIN

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shaw0486

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HELLO,
I AM WORKING ON A FEEDER CALCULATION. I AM HAVING TROUBLE LOCATING THE INPUT AMPS FOR THE ATTACHED LIGHTING FIXTURE. WHERE DO THE ENGINEERS GENERALLY GET THIS INFORMATION. I AM SOMEWHAT GREEN WITH THIS. ANY HELP WILL BE GREATLY APPRECIATED.
 

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The information you need is on the ballast. The fixture can be ordered with a few different ballasts, and you can choose a 120V or 277V ballast which will also affect the nameplate amps. So need to find the ballast electrical input information. For a ballpark estimate, most 4' T8 lamps are 32 watts each (F32...) and this fixture has four. I'd add a bit to cover power factor or something unusual if you can't get the exact nameplate value.

I've been surprised that the residential T8 fixtures I've been buying have a nameplate of 0.5 amps (at 120V) for a two lamp F32T8 ballast. Thought it would have been at least .55 or more.
 
shaw0486 said:
HELLO,
I AM WORKING ON A FEEDER CALCULATION. I AM HAVING TROUBLE LOCATING THE INPUT AMPS FOR THE ATTACHED LIGHTING FIXTURE. WHERE DO THE ENGINEERS GENERALLY GET THIS INFORMATION. I AM SOMEWHAT GREEN WITH THIS. ANY HELP WILL BE GREATLY APPRECIATED.
Click to expand...

The fixture itself should tell you the maximum wattage lamps it can take thats what you use in your load calcualtion for branch circuits NEC 2008 220.14 (D). If the lights are on for more than 3hrs then you have to calculate it as a continous load (ie 125%) . For feeders, you use the table 220.12 assuming this lighting is listed in one of them assuming the actual load is less than the table, if not then you use the actual load, which ever is greater. And remember if there is no demand factor for the feeder load you're doing, then you might have to add 125% in the feeder as well for continous load for the lighting. Hope this helps.
 
This particular spec sheet does not give you that information. It does say this fixture can be used with either 1 ballast [supplies all 4 lamps] or 2 ballasts [which supply 2 lamps each]...also, this fixture is available with 120v or 277v [that's a ballast issue].

Without knowing which voltage and configuration there's no real accurate way to determine the exact amperage [i.e. rating of the ballast(s)].

...what is this? 3 guys decide to answer at once!
 
brother said:
The fixture itself should tell you the maximum wattage lamps it can take thats what you use in your load calcualtion for branch circuits NEC 2008 220.14 (D). If the lights are on for more than 3hrs then you have to calculate it as a continous load (ie 125%) . For feeders, you use the table 220.12 assuming this lighting is listed in one of them assuming the actual load is less than the table, if not then you use the actual load, which ever is greater. And remember if there is no demand factor for the feeder load you're doing, then you might have to add 125% in the feeder as well for continous load for the lighting. Hope this helps.
Click to expand...

For the fixtures in the OP (ballasted florescent) isn't the actual reference 220.18(B) and, as mentioned, is based on the amperage of the ballast not the lamps?
 
infinity said:
For the fixtures in the OP (ballasted florescent) isn't the actual reference 220.18(B) and, as mentioned, is based on the amperage of the ballast not the lamps?
Click to expand...

Good article point. But I think we are basically saying the same thing, the one I referred to NEC 2008 220.14(D) is dealing with mostly the outlets and it does say the maxium va rating of the 'equipment' and lamps for which the luminaire is rated. The ballast is going to help determined the maxium that is allowed for that fixture, or what that fixture is rated for :). I don't think anyone is going to put in more lamps or higher wattage lamps than the ballast can handle. ;-) At least thats how I reconcile those 2 articles.
 
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