Question: Are the amps listed on a fluorescent light ballast the amount continuously drawn, or the max under certain conditions?

I recently installed some older T-12/magnetic ballast lights in my basement (got them at a good price). I added up all the amps and it comes to slightly over 18 amps. I wanted to test the illumination so I temporarily connected them to a 15 amp circuit, and it didn't trip the breaker. I've tested for several days, hours at time, with no problem. I still plan to upgrade the circuit or possibly split the lights on two circuits. Just wonder if I'm missing something here as this will help in my wiring plans. Thanks

Ballast amperage would be the maximum for that ballast.

Amperage used would be determined by the number and size of the bulbs.

For instance two 40 watt bulbs would draw a total of 80 watts.
80 watts divided by 120 volts would be .666 amps.

So, count the number of bulbs, multiply by the watts and divide by 120 for total amps on the circuit. Doubt that you could exceed 15 amps in a basement.

HK, thanks. Using that calc I have slightly over 13 amps-I installed a lot of lights w/40 watters. Will up grade to 20amp/12 gage.

Will up grade to 20amp/12 gage.

OK, but should not be necessary.

HK, thanks. Using that calc I have slightly over 13 amps-I installed a lot of lights w/40 watters. Will up grade to 20amp/12 gage.
Pick up a clamp on ammeter. The calcs are just to get you close, never exact.
Too many factors to consider, from input voltage, length of circuit voltage drop, type and wattage of bulb. It's unlikely you will have to change the circuit.

The rated current for a fluorescent fixture is written on each ballast...
the lamp wattage may not always give you the correct current draw as there may be a power factor to the ballast.