Path to ground in a three phase system

[overamped]

First off since joining this forum I've learned a heck of lot so thanks to all who post. Second I'm trying to wrap my head around the path to ground in a three phase system. If it's the grounding conductor when it's bonded to the Neutral bus that facilitates the operation of the over current devise. What happens when it's a three phase system that does not have a neutral tap? Is it one of the phases? They are ungrounded conductors so I would not think so.

 

[iwire]

If it is a straight 3 phase supply system you either ground one of the phase conductors at the source making it a corner grounded system or you don't ground it at all and you have an ungrounded system. Ungrounded is allowed for some applications.

 

[SG-1]

If the system is ungrounded then a ground detection system must be used to alert personal if a ground fault occurs.

 

[tom baker]

A grounded system (see 250.20 for systems that must be grounded) has a main or system bonding jumper connecting the grounded conductor to ground and to the equipment grounding conductors. Without the bonding jumper, the ground fault current can't get back to its source which is the windings of the supply transformer, and hopefully will open the overcurrent device
An ungrounded system does not have the bonding jumper, a ground fault won't open the overcurrent device, and this system is often used in industry for systems that should not shut down, but as pointed out, have a ground fault detection system.

I highly recommend Mike Holts Grounding Vs Bonding DVD. with it you will gain a great insight into grounding and bonding.