# Fluorescent amperage

• posted on October 7, 2006, 5:39 pm

How much current is drained by a 2x 40 watt T12 magnetic ballasted shop light trough at peak current draw? I assume this is at startup, while trying to saturate the transformer and ignite the tubes. How much is drawn once the lights are running?
Short version: How many such fixtures (too cheap to replace the old ones) can be run on a 15 amp circuit?

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• posted on October 7, 2006, 7:15 pm
On 7 Oct 2006 10:39:25 -0700, "Father Haskell"

I don't know

15A x 120V = 1800W You can only use 80% 1800W x 0.8 = 1400W (2x40) = 80W per fixture 1400W / 80W = 18
18

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• posted on October 7, 2006, 7:16 pm
15a x 80% = 12 a. Different ballasts will have a small margin in amp draw per ballast.
Does it not say on the ballast amps?

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• posted on October 7, 2006, 7:59 pm

I have an old textbook that says to allow 20% of the total lamp wattage rating for power to the ballast. That would mean 1.20 x 2 x 40 watts = 96 watts total power consumed (not appartent power) for a simple dual-40 fixture.
Maybe the new electronic ballasts are more efficient than this?
Beachcomber

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• posted on October 7, 2006, 8:07 pm
On Sat, 07 Oct 2006 19:59:33 GMT, snipped-for-privacy@notreal.none (Beachcomber) wrote:

That is lamp wattage. Not the ballast.

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• posted on October 7, 2006, 8:30 pm
The electronics are a lot better. Less amp draw Less heat The frequency on the output of the ballasts driving the lamps makes it better on the eyes. On the ones I have installed anyway.

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• posted on October 7, 2006, 9:55 pm
Most building codes require limiting lighting to 80% of the circuit load. The idea is that it could be on for long time and things will heat up. It also allows for the fairly minor start-up issues. For a 15A breaker at 120V thats 1440watts.
Your ballast should state it's amperage on the lable. Beachcombers 96W is about right. Any way you look at it you get quite a few fixtures! If you are running many fixtures for any length of time you can save a lot of money with new fixtures. ( 2 "T8" lamps, give more light, last longer and usually need about 0.52 amps. That's almost half the power!)
Richard Reid, LC Luminous Views
Beachcomber wrote:

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• posted on October 8, 2006, 12:30 am
Beachcomber wrote:

So I could just round up to a nice, easy 100 watts per fixture and calculate from there. Thanks.

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• posted on October 7, 2006, 10:43 pm

and `1800W x`80% = 1440W.

--
79 days until the winter solstice celebration

Mark Lloyd

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• posted on October 8, 2006, 12:51 pm
On 7 Oct 2006 10:39:25 -0700, "Father Haskell"

I believe you need to check each ballast power rating, not the bulbs.
Also, you have to figure if the usage is continous, or not continous loads.
later,

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• posted on October 8, 2006, 1:17 pm
Fluroscents use little power I have about 20 in my shop on a single 15 AMP breaker.
The starting current is no doubt higher than run but the typical breaker carries the load fine, like a slo blow fuse..
my fixtures are all old cheap ones dating back to about 1983 or so when i started my business

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• posted on October 8, 2006, 7:29 pm

The USA-usual "traditional" high power factor 2xF40T12 rapid start ballast that is about 8.25 inches long, 9.5 inches long including the mounting flanges, 2.25 inches wide, 1.5 inches thick, rated "Class P" (having a thermal cutout), and noted as having "high power factor" typically draws .8 amp when the lamps are running and less when the lamps are starting.
I would not push the limit of the circuit. Somehow I would rather not put more than 12 of these on a circuit, and first actually read a ballast label for the current draw.
http://www.codebookcity.com/codearticles/nec/necarticle210.htm - with a few notes from the National Electrical Code - states that a continuous load shall not exceed 80% of the rating of the circuit.
If the ballast has a shorted internal series capacitor, then it will draw much more - I would hazard to guess 1.5 to 2 amps. The "Class P" thermal cutout switch will not always cycle on and off when that happens, but lamp life is usually noticeably reduced and the lamps may not look much brighter. However, I consider it a safe bet that probably none to at worst few of your fixtures will have that problem, and never will most have it before you notice and replace the ballasts.
The shorter length ballasts used in cheap shop lights can do anything, but usualy draw similar current (near or somewhat under an amp), usually result in less light output, sometimes maybe often result in shorter lamp life, and often require the fixture to be suspended in mid-air (such fixtures usually come with chains) so that the ballasts do not overheat. Those ballasts are sometimes called "residential grade", and my impression is that a better name for such grade is "stool specimen".
- Don Klipstein ( snipped-for-privacy@misty.com)

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• posted on October 8, 2006, 9:34 pm
Don Klipstein wrote:

25 x 30 ft. shop has two 15 amp lighting circuits currently supporting 2 2 x FT40 fluorescents each. Would like to increase that to 4, maybe 8 fixtures per circuit, plus spot and task lights. The latter can be CFL or some other high efficiency lamp. I really only need to spot illuminate
the tiny area where a cutting tool meets a workpiece; 20 watt krypton spots might work better than fine enough.

Again, the short story is, I'm not eager to replace my 100% reliable 30 year old Sears lamps with Lights of America junk from HD.

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• posted on October 8, 2006, 10:39 pm

my fixtures date back to 1983 or thereabouts, other than a couple broken sockets and new lamps never a problem.

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• posted on October 9, 2006, 4:18 pm
The replacement question is mostly related to how much time you have them on. If you're a business then you can pay for new top quality fixtures in year or two (depending on lots of other factors.) If its a home shop that runs 10 hours a week, keep your old stuff.
1000 watts (10 fixtures) x 10 hours x 50 weeks = 500 kilo-watt-hours (KWH) at \$0.15 (high guess) = \$75 per year for power. You could save the price of one good fixture a year.
Raise that to 50 or 75 hours a week and you start getting somewhere.
BTW you don't have to buy the same type of old fixtures, or the el-cheapo HD. There are lots of good fixtures out there.
RickR

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• posted on October 9, 2006, 5:12 pm
My plan when I get some time, my shop is my basement often I am JUST passing thru, not doing any detail work.
But each time I must turn on ALL the lights.
So I am going to split the light circuit, just a few for walking thru, a second switch for being here doing something that needs brite lights.
Over time this will certinally save me replacement fluroscent bulbs and some power.
Probably way more money than replacing all my lights I have at least 15 fixtures plus a couple spares.
whatyever I do I will wire it that turning off main lights kills everything so I cant accidently wonder off leaving machines heating:(
I have a buddy who left a soldering iron on while on a weeks vacation, lucky he still had a home when he got back.......

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• posted on October 9, 2006, 3:34 am
Don Klipstein wrote:

Humbug. I have a bunch of these "cheap lights" three currently operate in my garage/workshop, the others have been used for Grolux operation. Never had a problem with any of them. And yes, the fixtures including bulbs cost less than a replacement ballast from an electric shop.