Max number fluorescent fixtures per circuit?

[jvitez]

Lithonia's Visual basic software gives me 30 two-lamp T8 fixtures for my garage, or 1920W. This would mean exactly a 20 amp circuit when calculated for continuous loads. This leads me to my question: is there a maximum number of fixtures per circuit based on the fluorescent ballast?

For example (hypothetical only), what if I wanted 60 two lamp fixtures on 1 circuit? This would calculate to a 40 amp circuit. Would it be possible? Possible but not allowable? Or would the large current flow overheat all the ballasts?

 

[porschedude996TT]

I think it is 80% of what the sum of the input load on the ballasts. Can't use just the tube wattage because that doesn't account for the ballast loss.

 

[jvitez]

Rats! I posted in the wrong section. Mods please move me. Sorry about that chief!

Yes, 80% for continuous loads, but I wonder if their is a current limit for each ballast. Large warehouses must have a huge number of fixture on one circuit, but I wonder if commercial ballasts have a different rating. Or does it matter?

 

[Garyl53]

It doesn't matter how many fixtures as long as the breaker is sized properly and the wire is sized to the breaker rating. The reason for many circuits is to keep the wire size down so it is affordable. Commercial buildings often use 277V for lighting to keep the current lower to support a large number of fixtures.

 

[Garyl53]

Also to add additional info. The Lithonia sold at HD have a rating on 0.8A @ 120V= 96W for each fixture (on the box). I would assume this takes into account for start up surges, low voltage brownout situations and the proper derating. So for 30 fixtures @ 96W each would be a total of 2880 Watts. Perhaps their software takes into account some actual measurement info versus the box maximum rating. I would create several sub-circuits and switch banks for the lighting. I wouldn't go for more than 20 fixtures on a 20A breaker also.

 

[jvitez]

That's the info I was looking for. Thanks a bunch!

I now know what to look for on the box to do my calculations. I was planning on about 3 switched banks anyway, but now I can make it 2 circuits. Much appreciate your help.