lighting load

[equatorman]

Any feed back on my question?

 

[GoldDigger]

Thanks for your reply GoldDigger. So if you had a bunch of fixtures I guess you would just multiply .80A by the number of fixtures and load the breaker to no more that 80 percent. Am I correct on this?

Looks good to me.

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[equatorman]

Thanks GoldDigger.

 

[Electric-Light]

Gentlemen, I was reading in a text book that for fluorescent lights the lamp ratings should not be used for load calculations. Ballast ratings should be used instead. I asked two guys on the job and they said they always use the lamp ratings. So I am totally confused now.
If you have a fixture with a single 120v ballast rated at .80A that takes two 4ft 40watt lamps, how would you calculate the load?
Thanks for your help. Remember I am fairly new to this.

No, you're not supposed to even though it may work fine mostof the time but it's not going to work out every time and that one time can be very costly. There weren't that many variations of F40T12 ballasts and all makes and models for general purpose applications gave close enough estimate by using lamp ratings.

The most common T8 ballasts are 0.88 and if you're talking 120v 1/4A per lamp gets you pretty close with a bit of margin in most cases. If the fixtures original to the building used 0.5A rated ballast and the existing branch are right at the max, you could run into problems. Normally lighting upgrades don't add power, so it's uncommon but here's an example.

You are modernizing with controls and dimming ballasts. Dimming ballasts are available in a several different ranges like 0.05 to 0.88/1.00/1.20. The maximum setting with higher ballasts give more output than 0.88, but they have higher amps. The 1.00 will likely be rated 0.6A. You'd look for another dimming ballast that is rated at 0.88 maximum if you'd rather not upgrade the circuit. This can get very costly if you discover after everything is installed.