Role of EGC in balanced system

[hhsting]

In a perfectly balanced three phase system understand that neutral still needs to be brought to service disconnect. From service disconnect equipment grounding conductor would be brought downstream up to the equipment.

I am guess but not sure Their is no ground fault it’s perfectly balanced three phase system. There can be phase to phase fault. What would be purpose of EGC in terms of what fault it carries? What fault current would EGC encounter in conductor back to utility? Phase to phase, phase to ground???

 

[LarryFine]

In a perfectly balanced three phase system understand that neutral still needs to be brought to service disconnect. From service disconnect equipment grounding conductor would be brought downstream up to the equipment.

Correct. The premises EGC system begins where the neutral bond is made and grounded by the GEC system. The neutral may or may not be needed beyond that point

I am guess but not sure Their is no ground fault it’s perfectly balanced three phase system.

Not correct; there is no neutral current. Only a non-grounded system would (theoretically) have no fault current resulting from a (single) phase-to-ground fault.

There can be phase to phase fault. What would be purpose of EGC in terms of what fault it carries? What fault current would EGC encounter in conductor back to utility? Phase to phase, phase to ground???

A fault involving the premises EGC would be phase-to-ground current on the load side of the main/bonding point, but would actually be phase-to-neutral current on the line side of the main.

That's why bonding the EGC to the neutral is important.

 

[don_resqcapt19]

Ground fault are possible in all systems, both grounded and ungrounded. The type of load has nothing to do with this. A ground fault is simply an unwanted connection between an ungrounded conductor and something that is conductive and has a connection of some type to the grounded conductor of a grounded system or to the earth on an ungrounded system. A ground fault on an ungrounded system will result in a very low ground fault current, a ground fault on a grounded system will result in a significant amount of ground fault current.
The EGC is only involved in ground faults, it plays no part in line to line faults.

 

[jaggedben]

What they said.

Put another way: If there is a ground fault, then the three phase system will be absolutely for sure no longer 'perfectly balanced'.