Portable Generators

[Dave w]

A company where i work is having its main transformer changed, in its place they have a portable generator, wired directly from the portable generator to a main panel.Coming from the transformer the feeds, neutral and ground are disconnected.
My question is, should the portable generator be grounded to a grounding electrode.

 

[iwire]

Re: Portable Generators

If the generator is tied into the buildings service gear it is connected to a grounding electrode(s).

 

[pierre]

Re: Portable Generators

If a transformer is being repaired, and this "portable" generator is supplying the load, I do not think it falls under 250.34(A). I think it falls under 250.34(B)Vehicle-Mounted Generator.

These are portable in a sense (delivered to the jobsite via truck). Is this unit on the frame of a vehicle? or is is portable such as the 5000 watt type?

If of (B), the installation described would require a ground rod driven.

 

[don_resqcapt19]

Re: Portable Generators

Pierre,
The code does not require the use of a grounding electrode at the generator, only that is be connected to a grounding elecrode. This connection will be via the cables to the building and the main bonding jumper at the building disconnect.
Don

 

[pierre]

Re: Portable Generators

For most generator applications, I agree with your statement.

When a vehicle mounted generator is brought in to supply power to the building temporarily (because the Utility transformer is now being repaired, hence there is no grounded conductor supplied to the building), it now becomes the means of supply to the building, providing the phase conductors as well as the grounded conductor. At this point, the grounded conductor at the generator needs to be grounded, and should be locally grounded near the generator, just as the Utility's transformer is grounded before the conductors enter the building.

 

[don_resqcapt19]

Re: Portable Generators

Pierre,
The code does not specify the required location. If the neutral is not bonded at the generator and if the ungrounded, grounded and grounding conductors are run from the generator to the service disconnect, I see no code reason or electrical reason to install a grounding electrode at the generator.
Don

 

[jwelectric]

Re: Portable Generators

No statement has been made about how many conductors are coming from the gen-set.
If there is an equipment grounding conductor being routed with the supply conductors from the gen-set would this have anything to do with the electrode arrangement?

 

[LarryFine]

Re: Portable Generators

Originally posted by jwelectric:
No statement has been made about how many conductors are coming from the gen-set.
If there is an equipment grounding conductor being routed with the supply conductors from the gen-set would this have anything to do with the electrode arrangement?

Mayhaps. I envision a GEC connection where the neutral and EGC are bonded, i.e., the main bonding jumper, as per Don's initial response.

 

[mpd]

Re: Portable Generators

dave

need more info

 

[tom baker]

Re: Portable Generators

"No statement has been made about how many conductors are coming from the gen-set.
If there is an equipment grounding conductor being routed with the supply conductors from the gen-set would this have anything to do with the electrode arrangement?"
No.
Grounding electrodes are only required for a seperatly derived generator. If the generator neutral conductor is solidly bonded to the system neutral, then its not a seperatly derived generator.