watts per fixture?

I am unsure of how to properly calculate the watts per fixture so that I might try filling out this comparison tool (for both current system and proposed system): Cost of Waiting Estimator | Energy Usage Tool | GE Lighting North America
Say for example the current system uses three T12 F40 lamps per fixture. Would that simply mean I'd multiply 40 (watts) x 3 (lamps) to find the current watts per fixture, or do the ballasts also figure in to the calculation? Thanks for any help.

 

I habitually allow 40W per lamp when installing 32W T8 lamps, to allow for ballast load, so I'm guessing the older ones might work that way too. That said, I can always double-check by reading the ballasts once the new fixtures are on the job, or by looking up the spec sheets before the truck shows up.

What is the information on the ballast labels?

 

What is meant by "ballast load", please?
Comment quoted above: You're referring to simply reading the ballast label (or looking at the specs), correct?
Well, there is Hz information, doesn't seem to be any info on these old magnetic style ballasts in regard to how much wattage the ballast might use. I'm unclear on what kind of info I might need to find/determine "ballast load" if that's what I need.
Thanks

 

On one of the old ballasts, the Advance catalog number HM-140-1-TP the label looks like this http://i207.photobucket.com/albums/b...psab2a9ea8.jpg and I've had no luck finding any spec sheet for this basically obsolete model.

 

That would be the current consumed by the ballast. Yes, a magnetic ballast like you have uses power just like the lamps do. No, they aren't very energy efficient and that's why they are no longer manufactured. If you figure 20 to 40 watts per ballast you'll be fine.

 

Okay, thanks CasualJoe. Yeah we've got some fixtures that use the magnetic ballasts along with three of the F40T12 4’ 34W lamps. So, if I can figure 34 x 3 = 102, plus 30 watts per ballast (per your 20-30w suggested estimate), I'd have a total of 132 watts per fixture. That seems to jive very closely to what I just came across here http://www.xcelenergy.com/staticfile...tage-Guide.pdf where on the bottom line of the first page it shows total wattage for three such lamps in a magnetic ballast being 127 watts.

 

And so now I have another question. The "input watts" spec as described for this particular T8 ballast is shown as 65-85w GE LIGHTING Electronic Ballast, T8 Lamps, 120V - Electronic Ballasts - 1PCW1|GE-332-120-N - Grainger Industrial Supply.
Is that the same as the ballast load (or current consumed by ballast)? Or does it mean something different?

 

Yes......input watts is the same as ballast load or current consumed.
It varies based on the exact type of lamp and quantity.

 

Right. That label says "Line Current .45 Amp." So that's a load of 54 watts. The diagram appears to show that that ballast supplies a single 40W T12 tube. If so, the ballast load is 14 watts. One of the more efficient models, apparently.

 

Okay so if I had fixture that uses three F32T8 lamps that would be 96w total for the lamps. And if the fixture was using a ballast such as the one shown in the link I posted (#7 this thread), which has input watts of 65-85w, that means the total watts for that fixture would be the 96 plus the other 65-85? That would be a total wattage of 161-181w for the fixture. Is that correct? That amount is way higher than the 86.2 total watts shown for three F32T8 4’ 32W lamps with an electronic ballast as listed on page 4 of this chart here http://www.xcelenergy.com/staticfile...tage-Guide.pdf
I'm confused.

 

If the ballast load is 14 watts, then what is the load of 54 watts you mention? When/how would it use 54 watts?

 

When it is on. 54 watts is the lamp load and the ballast load added together.

 

Okay, got it. Thanks. A 14w ballast running a 40w lamp. 14+40=54. I see.
Can you tell me what is the apparent formula for calculating ballast load from the "line current" spec and the number and type of tubes? In other words, how did you come up with the 14w ballast load for that ballast? Please. Thanks.

 

Sure. .45A X 120V = 54W. 54W - 40W = 14W.

 

I see. How about the case where the same ballast were running a single 34W T12 tube? Would that lessen the "line current" number? If so, to what, and how is that figured? If not, could I get the explanation otherwise please.

 

IDK. It might drop the total to 48W and it might leave the ballast load at 20W. Will a 34 W lamp work with that ballast?

 

Yep, been running 34W on it, and others, for a long time, with no apparent problem.
I also have some old magnetic ballasts that run two T12 bulbs. The label on those says .77A line current. So what might be the total wattage used with those ballasts and two 34W T12s?

We have really old style magnetic ballasts in each fixture. Each fixture uses three F40T12 4' 34W tubes, with two ballasts. One ballast runs one of these tubes, and one ballast runs the other two tubes. So, looking at what's listed on this chart http://www.xcelenergy.com/staticfile...tage-Guide.pdf I can see that the 2-lamp ballast with that size/type lamps would be using 78W total. And I can see that the 1-lamp ballast with that size/type lamp would be using 48W total. So those added up (78 + 48) equals a total of 126 total watts per fixture.

Now, if I want to replace the two separate old magnetic ballasts and three T12 tubes per fixture with a single new electronic ballast in each fixture that will be running three F32T8 4' 32W tubes, the retrofitted fixture(s) would then, according to the chart, be using a total of 86.2 watts.

What I don't understand is if there are three 32W tubes, which equals 96W, how can the total fixture wattage consumption be only 86.2W? That's less the total of the tubes, plus doesn't even take into consideration the power consumed by the electronic ballast. How this can be?