It's when the 3 phases are still in order, but attached to the wrong terminals. EG, instead of ABC on consecutive terminals, they might have CAB. So, if you, say, had an undervoltage on phase A, that undervoltage would show up at the B terminal instead of the A terminal. Not an issue for most power distribution, but it can be an issue for parallel systems and networks.
And yeah, my example wasn't rolling the phases, it was transposed phases and reversed rotation.
[This message has been edited by SteveFehr (edited 10-28-2006).]
