Source4 dimmer on 208v source

I'm not sure how you got to 3.3A, but when using 208V loads on a 2-pole circuit breaker there is no "per leg" in the calculation. The load is the same on both wires. Of course, the math does get a little more complicated if you're talking about a 3-pole circuit breaker with the potential for other loads across different legs.

That said, this is kind of a weird application because the voltage at the lamp is not 208V, but 120V. The dimmer just limits the maximum voltage being sent to the lamp. That means your power calculations should be based on a 20A 120V circuit and you ignore the fact that you're feeding the dimmer with 208V.

If the breaker is 100% rated, then you could use three 750W lamps *continuously. If it's an 80% rated breaker (typical thermal-magnetic), then you can still use three lamps intermittently, but would be limited to just two 750W lamps per circuit if you want them all on continuously.


*For reference, "continuous load" typically means greater than 3 hours, but thermal-magnetic breakers will have some variation depending on environmental conditions.

For those interested I got the answer to this question. As I suspected the dimmer basically works as a transformer for the line/load. It apparently has an efficiency of around 90%. So with a load of 750w under normal conditions the load would be about 833Watts divided by 208V comes to about 4 amps a leg or hot. Ultimately, its probably fine to use 4 on a 20amp breaker, but 3 is safer.