I'm upgrading a piece of equipment and I need to change the supplied power to accommodate the new device.

My old machine runs on a 3-phase 208V 30A dedicated circuit. The plug and receptacle are one of the NEMA 4 prong ones (don't remember, doesn't matter, I'm changing it). The breaker is a 3-pole, 30A Square D.

The new device requires an L6-30R receptacle and a single phase 208V 30A dedicated circuit.

Since the existing circuit is also 30A, I already have three 10ga wires pulled. Can't I use this circuit for the new device? I was planning on putting in a new single phase 30A breaker (2-pole) and just using two of the three wires (plus a ground).

My questions are 1) Can I do that? Will it work and is it proper? 2) If so, what do I do with the empty space left from the old 3-pole breaker? 3) What do I do with the extra wire? 4) Lastly, does it matter which two spaces I use for the 2-pole breaker?

If it's useful, I'll attach a photo of the existing breaker.

It's funny, I almost feel like I know what I'm doing. But barely. And only sort of.

 

If this is a normal NFB, you should be OK, what is done in some instances is to come out of one breaker and go back into the top of the 3rd (what would be unused side) and out the bottom for the second conductor.
This is to satisfy any current detection device in the breaker, not always necessary, but it does not hurt.
Any 2 of the 3 will work.
Max.

 

Thanks, Max!

 

Just disconnect and cap off the third wire. A 3-pole breaker will work fine with two (or even 1) pole being used. You could even do this at the outlet if more convenient.
/mike

 

Max,
I think your solution of looping from the bottom of the 3rd breaker to the top of the 2nd would be very difficult based upon the picture the OP gave us. In an isolated panel with individually mounted breakers, it would make sense.

 

Max,
I think your solution of looping from the bottom of the 3rd breaker to the top of the 2nd would be very difficult based upon the picture the OP gave us. In an isolated panel with individually mounted breakers, it would make sense.

Yes, I realized after this was a panel breaker, rather than a single disconnect type.
Max.