120/208v 3phase used to step up to 480v?

[Benton]

When you use 120/208 3phase to step up to 480v and you bond x0 to B phase and so on how is it that the equipment being fed from the 480v side works when you have 480v between A and C and B is bonded? I saw this for the first time tonight....

 

[brian john]

First XO should not be bonded to anything, and no neutral connected to XO.

Second you bonded the B phase (your choice noted above), The voltages are
A-B-480
B-C-480
A-C-480

A-Gnd-480
B-Gnd-0 ZERO VOLTS
C-Gnd-480

B is grounded so the voltage has to be ZERO VAC between B phase and ground. From an operational stand point the equipment could care less if ground exist or not. You need ground B phase so if you have an A or C phase fault, you could operate ungrounded, or ground any one phase and the equipment could care less.

You could operate a wye ungrounded (NOT PER NEC) or ground any one phase and the equipment could care less as well. Assume you gground B phase in a wye

A-B-208
B-C -208
C-A-208
A-N 120
B-N-120
C-N-120
A-Gnd-208
B-Gnd 0 VAC ZERO VAC
C-Gnd-208
N-Gnd-120

 

[Benton]

Thanks!

 

[kwired]

You did not change voltage between any points of the system. You can ground any point in the system and those voltages will not change. Only thing that changes is which point has same potential as ground.

You can do same with any system that has a neutral. The neutral is not grounded in those systems until we connect it to ground. If you were to connect any other point to ground instead of neutral nothing happens other than voltages from all other points to ground will change, point to point voltages in the system will remain the same.