NEC 408.3.E: 3-Phase Busbar Arrangement

[MitYeltu]

NEC 408.3.E reads as follows

The phase arrangement on
3-phase buses shall be A, B, C from front to back, top to
bottom, or left to right, as viewed from the front of the
switchboard or panelboard. The B phase shall be that phase
having the higher voltage to ground on 3-phase, 4-wire,
delta-connected systems. Other busbar arrangements shall
be permitted for additions to existing installations and shall
be marked.

Have I missed the boat on this? A 3-phase system with a higer voltage on phase B than on phases A and C? I don't understand this. I thought a 3-phase system was, barring unbalanced impedances, balanced. What did I miss here?

 

[anorlunda]

Have I missed the boat on this? A 3-phase system with a higer voltage on phase B than on phases A and C? I don't understand this. I thought a 3-phase system was, barring unbalanced impedances, balanced. What did I miss here?

Nothing. You are right. I have no idea why they said B is higher.

 

[Averagesupernova]

With High leg Delta configuration, ground is connected to the center tap of one of the transformers. It is then impossible to have all three legs at the same voltage in reference to ground. Which one you want to call A, B, or C is whatever someone decides.
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When referring to buses, the terminology should be legs, not phases. A phase is a pair of conductors. Ideally all three phases will have the same voltage.