When to have a separately derived system (perm. generator)?

[zooby]

It is very easy to find info on the grounding and bonding requirements but I am not having much luck on "the why and when". Our campus has several permanent gensets at various buildings. To the point....There is one building where the ATS switches the grounded conductor. The building is our Veterinary hospital. Should this give me a clue that happens mostly in a "healthcare" type structure? TIA--

 

[tom baker]

Typically you will use a 4 pole transfer switch where there is ground fault monitoring, other wise the ground fault monitor will not work. Cummings/onan has some very good technical info on this.
GF monitoring is required on 489/277 1000 amp services, feeders and BCs.
But I have seen generators set up with 4 pole xfr transfer switches (or 3 pole on single phase) where not required.
The IEEE Green Book (grounding) covers generator grounding well.

 

[zooby]

Typically you will use a 4 pole transfer switch where there is ground fault monitoring, other wise the ground fault monitor will not work. Cummings/onan has some very good technical info on this.
GF monitoring is required on 489/277 1000 amp services, feeders and BCs.
But I have seen generators set up with 4 pole xfr transfer switches (or 3 pole on single phase) where not required.
The IEEE Green Book (grounding) covers generator grounding well.

thank you !

 

[Strathead]

Typically you will use a 4 pole transfer switch where there is ground fault monitoring, other wise the ground fault monitor will not work. Cummings/onan has some very good technical info on this.
GF monitoring is required on 489/277 1000 amp services, feeders and BCs.
But I have seen generators set up with 4 pole xfr transfer switches (or 3 pole on single phase) where not required.
The IEEE Green Book (grounding) covers generator grounding well.

That was what an Engineer who designs hospitals also told me.