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:
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?

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