I was under the impression that with poly-phase circuits, any circuit protection was required to de-energise all phase conductors at the same time, not only for worker safety reasons, but for the protection of motors (ie: Single-phasing protection).
I thought that was what they made 3 pole breakers for?
But yes Ghost is correct, however in any well-balanced 3-phase system, the neutral carries little or no return current.
Having said that, when have you last seen a perfectly balanced 3-phase system?
One other thing, some people seem to think that the neutral is dead (with it being called the "grounded" conductor in the circuit (even single phase circuits), this idea has killed I don't know how many electricians working in panels and DIYer's at light fittings.
It's not dead unless there is no power on the circuit at all.
Edited by Trumpy (01/14/09 05:56 PM)
Edit Reason: To add extra things
Let's face it, these days if you're not young, you're old - Red Green