When wiring up electrical service configured as 3-phase corner-grounded
delta, it would seem that the appropriate way to connect overcurrent
protection would be to make the 2 ungrounded wired breakable, and pass
the grounded wire straight through. That would imply using equipment
that is wired the same way as center-tapped 1-phase. NEC states that
a 2-pole breaker must not be used for such service unless it is marked
as being rated for both 1-phase and 3-phase (240.85). I would presume
that is because of the higher hot-to-ground voltage and the effect it
could have on interruption capability (as in NEC note in 240.85).
Is a 2 pole plus neutral breaker panel what is typically used for 3-phase
corner-grounded delta? I can't imagine using a 3-phase panel for this.
Are such breakers readily available?
Does the higher hot-to-neutral voltage decrease the interruption current
rating, considering that the neutral wire isn't passing through the breaker
(disregarding GFCI breakers where the neutral wire is involved).
Would these or other issue vary whether the configuration is closed-delta
or open-delta ("V")?
Are corner-grounded delta configurations ever used at voltage levels above
240 volts (in the US), such as maybe 480 volts or 600 volts? Have utilities
ever used it for primary distribution?
FYI, I'm not referring to delta configurations where one of the windings is
center-tapped to get 240/120 volts for conventional single phase compatible
18 years ago