Grounding generators with 4 pole transfer switches.

[jerry bass]

It is generally understood that emergency generators do not require ground rods and nor main bonding jumpers at the disconnect. This becomes a different scenario when 4 ATS switches are involved. Because the building / Utility neutral gets replace with a generator only return current pathway. And the main bonding jumper to the grounding electrode system is now removed from the system as well. Usually found at the point of main disconnect for the utility feed (Service). Now the ground rod. And potentially other present grounding electrodes need to be bonded to a main bonding jumper at the generator disconnect?

 

[jerry bass]

4 pole ATS

 

[infinity]

If you have 4 pole transfer switches don't you have a generator that is setup as an SDS? Wouldn't the SDS then require a SBJ and connection to the building GES?

 

[jerry bass]

What is an SDS? This was a project about 15 years ago. It had three output breakers feeding the Em input on 3 - 4 pole ATS( each had normal feed from the building
Main switchgear) I connected the generator ground to a ground rod and to the grounding electrode system ground bar beside the main switch gear. When the ATS operated the neutrals from the main switch gear were disconnected from the load neutrals and the generator neutrals became the line. But because of the main bonding jumper in the switch gear there was still a potential backfeed (through electrode ground bar) of generator neutral current to the utility (there being a main bonding jumper in the generator cabinet to return fault current) . It seemed to me it defeated the safety factor of the 4 pole design. Why the 4 pole switches then?

 

[LarryFine]

The basics:

If you switch the neutral, each source should be bonded, and the load not bonded.

If you don't switch the neutral, each source should not be bonded, and the load bonded.

Something like that.

 

[jerry bass]

Ultimately what happened. Except each source was bonded to the same set of electrodes and the neutral s were switched.

 

[qcroanoke]

The basics:

If you switch the neutral, each source should be bonded, and the load not bonded.

^^^^^^^^^^^^^When switching the neutrals bond neutral to ground in both sources and you're gold.
Basically treat them both like you would a service.

 

[LarryFine]

Except each source was bonded to the same set of electrodes . . .

I don't believe that's a problem.

 

[roger]

I don't believe that's a problem.

It's not.

 

[roger]

What is an SDS?

See article 100 Separately Derived System.