Question on lighting MWBC calculation

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GaTech04

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I'm about to start a project that has an area with 45 hi-bays. Each hi-bay has six 57W CFLs, with 2 lamps per switch leg to give a dimming effect.

I just want to make sure I cover all my bases for a proper install.

Without taking into consideration the ballasts' effect on the amps/fixture, is it safe to just go by:

57W x 2(per switchleg) x 45 (fixtures) / 277V = 18.52 Amps on each phase

Would it be acceptable to use three 30A OCPD circuits extended to a bank of three 30A rated switches which then extends to each of the fixtures. Each fixture will have a 30A rated 4W+G cord and plug for disconnecting means.

Thanks for the help like always!
 
augie47

augie47

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I'm not as well versed as I should be on this, mostly because I have seldom seen it in the field, but I think (don't hang your hat on this) that hidden in the wording of 210.21(B)(3) exception and 410.62, you can use a receptacle with a rating less than 30 amps.
Perhaps someone more well versed will advise us.

I would check the manufacturing instructions to see if they have any limitations.

I will add that I have seen hardwired fluorescents on 277v 30 amp circuits and shorted ballasts are not a pretty sight.
 
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GaTech04

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Im really not sure - I havent seen the fixtures, as they are being supplied by the owner. I do have the cut sheets, but I dont see it mentioned.

Should I try to contact to manufacturer or is there an easier way to determine if they can be on a 30A circuit?

Thanks!
 
augie47

augie47

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If you have time, be patient and see what gets posted here. This Forum is a wealth of info normally.
 
Smart $

Smart $

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Location
Ohio
GaTech04 said:
Im really not sure - I havent seen the fixtures, as they are being supplied by the owner. I do have the cut sheets, but I dont see it mentioned.

Should I try to contact to manufacturer or is there an easier way to determine if they can be on a 30A circuit?

Thanks!
Click to expand...
There are two criterion to use lighting fixtures on a greater than 20: a) must be a non-residential installation, and b) fixtures must utilize heavy duty lampholders. [ref: 210.23]

If the cut sheet has no mention of heavy duty lampholders, they likely cannot be used on a greater than 20 amp circuit.
 
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augie47

augie47

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State Electrical Inspector (Retired)
Smart$, I am not disagreeing with you as I find myself at a bit of a loss on this thread knowledge wise. But, since the circuit is feeding the fixture (ballast) and not actually the lampholder, would it not fall under "utilization equipment" being fed rather than a "lampholder" being fed ?
 
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GaTech04

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Since these fixtures use ballasted CFLs I'm pretty sure they wont have HD rated lampholders. I think they are just the gx24q's I see in can lights.

I did e-mail the manufacturer to see what they had to say, but it looks like I will have to add in a 2-pole contactor for each phase to allow for the load.

Thanks again guys!

EDIT: I found this in the archives! http://forums.mikeholt.com/archive/index.php/t-84499.html

The commentary (although NOT enforceable) following 210.21(A) states:

The intent of 210.21(A) is to restrict a fluorescent lighting branch-circuit rating to not more than 20 amperes because most lampholders manufactured for use with fluorescent lights are not of the heavy-duty type and are rated at 660 watts or 250 watts.
Branch-circuit conductors for fluorescent electric-discharge lighting are usually connected to a ballast rather than to lampholders, and, by specifying a wattage rating for these lampholders, a limit of 20 amperes is applied to ballast circuits.
Only the admedium-base lampholder is recognized as heavy duty at the rating of 660 watts. Other lampholders are required to have a rating of not less than 750 watts to be recognized as heavy duty. The requirement of 210.21(A) prohibits the use of medium-base screw shell lampholders on branch circuits that are in excess of 20 amperes.
Click to expand...
 
Smart $

Smart $

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Location
Ohio
augie47 said:
Smart$, I am not disagreeing with you as I find myself at a bit of a loss on this thread knowledge wise. But, since the circuit is feeding the fixture (ballast) and not actually the lampholder, would it not fall under "utilization equipment" being fed rather than a "lampholder" being fed ?
Click to expand...
The full terminology used is "fixed lighting units with heavy-duty lampholders".
 
augie47

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
Thanks for the lesson this morning.
My belief was that they should not be on greater than a 20 amp, but I try to follow "Code", not my "beliefs".
Another education day.
 
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