EMI problem

[Shoe]

I have an issue where A/V equipment is being affected by EMI by fluorescent ballasts. The EMI problems only manifest when the fluorescent fixtures are on and can be seen with distortion on the overhead projector.

The fluorescent fixtures are 2x4 (< 10% THD ballasts) in a master/slave configuration. If you turn on half the lights (every other tube) on either side of the fixture, there is no EMI distortion. If you turn on all the lamps at once, you get EMI distortion.

The lighting circuit is completely isolated (separate hot neutral and ground) from the A/V circuits.

Could this be an issue with the master/slave wiring? I've had no issues like this in the past even when using master/slave.

Any thoughts or trouble-shooting ideas? This one has me scratching my head.

Thanks.

 

[Speedskater]

My guess is that when half the lights are on, the Hot and Return current paths are in close proximity to each other. But when all the lights are on the Hot and Return have very different paths.

 

[necnotevenclose]

and why are the lights on when the projector is on...just asking

 

[cadpoint]

My guess is that when half the lights are on, the Hot and Return current paths are in close proximity to each other. But when all the lights are on the Hot and Return have very different paths.

I was just going to guess 277V grey and ground crossed, or just a nicked neutral.

 

[Shoe]

Thanks. These are good suggestions. The contractor wants to swap out ballasts and remove the master/slave configuration for the light fixtures. I don't think this is a good idea.

I'm also leaning toward a wiring issue, but it is a matter of convincing the contractor