Machine Main Disconnect Lockout Neutral Question. 1

[wwilson]

I'm in the process of selecting a main power disconnect switch for a piece of equipment (208 3ph 5wire 40A). The switch is the Red/Yellow round door mount main disconnect/lockout type. Several manufactures have a late-break early-make neutral disconnect option. Is there a reason, code or otherwise, that I would want to disconnect the neutral conductor vs. just the three phase conductors?
Thanks, Wayne

 

[rbulsara]

If the system neutral is firmly grounded at the service, it is sized properly and continuity (back to service) is assured, a disconect with N is not required for a 3 phase 4 wire system (I beleive your 5th wire is ground) for low voltage equipment.


It is a practice in high voltage equipment to make sure neutral is also isolated when a large machine is being serviced. This is done to assure saftey against any phase to neutral fault occuring on a system, and if the neutral is not effectively grounded , it could raise the potential of a neutral during a fault which can be a potential danger to maintenace persons. However I do not think, it is a big concern for system rated 600V or less.

I must add, it is not against Code (NEC) to use such a (4 pole) disconnet or a 3 pole discoonect for that matter.

 

[jbartos]

Suggestions to wwilson (Electrical) Oct 22, 2003 marked ///\\I'm in the process of selecting a main power disconnect switch for a piece of equipment (208 3ph 5wire 40A).
///Assumed: 3-phases, 1-neutral, 1-ground.\\ The switch is the Red/Yellow round door mount main disconnect/lockout type. Several manufactures have a late-break early-make neutral disconnect option. Is there a reason, code or otherwise, that I would want to disconnect the neutral conductor vs. just the three phase conductors?
///The neutral is safer to be disconnected if it is not grounded and if the equipment is grounded by the equipment grounding system. If the neutral is also serving as the equipment grounding and there is not extra conductor for the equipment grounding, then it should not be disconnected.\\Thanks, Wayne