I have 6 fluorescent lighting fixtures in my garage each one has 2-40watt bulbs and they are all on a 20 amp breaker.My problem is when I go to use my plasma cutter my lights flicker like a strobe when I turn on the plasma cutter.Do I have too many lights on one circuit?I wouldn't think it would be.I checked all my grounds in the main circuit box and everything seems fine.Anyone have any ideas what it could be?Also I am using 12g wiring.and the plasma cutter is only drawing 27 amps when I cut steel with it.Thanks

You could be getting feedback from the machine. If there is enough it can cause your lights to go out of phase.

You could be getting feedback from the machine. If there is enough it can cause your lights to go out of phase.
Thanks,how do I resolve this problem with feedback?

I am not sure what kind of "feedback" and "out of phase" is being referred to. I will leave that to Cal to answer.

The reported symptom of lights flickering when the cutter operates can indicate a low voltage issue.

Either due to a long distance and/or small wire size of the feeder to the garage, or due to a loose connection somewhere in the wiring, panels, circuit breakers, etc.

Need to know the distance of the feeder to the garage and wire size.