High & Low voltages

[mivey]

You would need to test between the two devices to know for sure. I do believe that there is a phase arrangement that would give you less than 300 volts between a 277 volt switch and a 120 volt receptacle.

That would be when they have the same primary phase.

A quick crunch on the others:

With a wye-wye and no phase shift it would be 157.1 from phase a to a'. It would be 352.8 from a to b' or c'.

With a delta-wye and 30 degree phase shift, it would be 183.3 from a to a'. It would be 385.7 from a to b'. It would be 302.0 from a to c'.

If I did not flub the math, that is. I just used some quick vector math and positive rotation. The 380 and 381 in the graphics makes me wonder if I forgot something, but I have not had my donut yet so may not be thinking clearly.