common practice or code?

[GoldDigger]

Well I know when to throw in the towel, I would be lying if I said I fully understood what you all are telling me but I have to accept it regardless.

Now that you have thrown in the towel, I will make one more attempt at clarity.

If the 480Y/277 and the 208Y/120 services are produced by POCO transformers of the same vector group, fed by the same primaries, and somebody went to the trouble to match phase labels when all they were required to do was match rotation, then A will be parallel to A, etc. But can you rely on that? Probably not.
If one of the two voltages was derived by a transformer from the other, the odds that they are in phase drops even farther.

Both systems will still have A,B,C labels because it is hard to find A+30degrees, B+30degrees, C+30degrees labels these days.

 

[don_resqcapt19]

Would 2 delta-Wyes create the same phase shift when comparing secondary to secondary?

Only if the primary rotation is the same. Changing the rotation reverses the phase shift, so the secondaries could be out of phase by 60?.

 

[Canton]

If both the 120 and 277 are on the same phase I believe the result is under 300 volts.

interesting....you got me thinking about the phase shift and what the differenc in potential could be

 

[don_resqcapt19]

interesting....you got me thinking about the phase shift and what the differenc in potential could be

With the right combination of transformers and primary rotation you can get to 180? out of phase and have 397 volts between the conductors of the two systems.

 

[kwired]

Now that you have thrown in the towel, I will make one more attempt at clarity.

If the 480Y/277 and the 208Y/120 services are produced by POCO transformers of the same vector group, fed by the same primaries, and somebody went to the trouble to match phase labels when all they were required to do was match rotation, then A will be parallel to A, etc. But can you rely on that? Probably not.
If one of the two voltages was derived by a transformer from the other, the odds that they are in phase drops even farther.

Both systems will still have A,B,C labels because it is hard to find A+30degrees, B+30degrees, C+30degrees labels these days.

I think you are saying essentially the same thing here as I was going to mention - if you have a 480/227 and a 208/120 system both with same primary to secondary displacement, then you would have the 480 volt phase A "in phase" with the 208 volt phase A.

Plus if you have your own label maker "A+30" degrees is not that hard to come up with. So is a label that says "figure it out for yourself, I don't know what this is"

 

[mopowr steve]

I agree, is there also a possible configuration where it can be less than 300 volts?

Thanks for the illustration I forgot this one.
Don't you hate it when we forget more things than we've learned!