Permanent Generator Ground Rod?

[jhawkbb]

We are installing a generator for a piece of equipment that is 3 phase 480V no neutral. Is a switched neutral the only criteria for a SDS? What if you don't have a neutral as we do in this install? Ground rod for the generator or not? Generator is outside on concrete pad.

 

[zbang]

Regardless of SDS or not, you need an EGC. If the pad is up against the served building, you can get the EGC from there; if they're separated, then it probably counts as a separate structure and you'll need both a grounding electrode there and also a connection from the building's GES.

What is the system it's feeding (wye or delta)? Is that ungrounded? SDS is all about where the system bonding jumper is located.

 

[jhawkbb]

The main gear is 277/480 wye but the piece of equipment is fed from bus duct that doesn't have the neutral

 

[Smart $]

The main gear is 277/480 wye but the piece of equipment is fed from bus duct that doesn't have the neutral

Given the transfer switch (TS) has to switch all three poles and there is no neutral to switch, the generator side of the TS can be considered a completely separate system. You have the choice of running it wye-point grounded, B-phase corner grounded, or ungrounded. I would not opt for the latter two, but am willing to discuss if you really want to go that route.

That said, you bond the generator as a grounded SDS. As mentioned the need for a GES at the generator is typically based on generator proximity to the building or structure served but also whether the generator's first disconnecting means serves as the building disconnecting means (which the building GES is required to be bonded to). If it does not, and the first disconnecting means is remote to the building served and or integral with the generator, I'd just install two rods and be done with it.