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
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?
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?
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
Fluroscents use little power I have about 20 in my shop on a single 15
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
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
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 ( firstname.lastname@example.org)
25 x 30 ft. shop has two 15 amp lighting circuits currently supporting
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
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.
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.
Father Haskell wrote:
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
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.......
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.
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