Generator neutral bond design

Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I was wiring a trailer-mounted generator to a small building to serve as backup power while the permanent standby generator is repaired. The building's ATS does not switch the neutral, so I attempted to remove the neutral-ground bond in the generator. What I found was that the generator output neutrals were all attached to a threaded stud that is attached to the metal back wall of the control compartment. The jumper from the neutral stud to the ground bar has no effect in isolating neutral from ground because the stud is bonded to all the other metal in the generator & trailer frame!
I'm thinking of writing to the manufacturer to tell them their design is screwed up. Thoughts?

QAS bond.jpg
 
Some generator manuals provide detailed instructions on how to use as a non-separately derived source (unbond the N-G). Some that do not, might violate its listing (if it has one UL 2200) to unbond the N-G
 
The manual for this generator is rather useless, but the sales sheet or "Product Reference Sheet" clearly says, "Neutral bonded to Ground with a removable bonding link accessible in the control cubicle"
I even called support, and they had little idea what I was talking about.
 
Since the neutral/ground bond is intact in the building, what would be bad about running the temporary feeder without an EGC, effectively mimicking a utility service?
 
Is it a rental generator?
If they own it I'd offer to put in a floating neutral bar.
 
Electromatic said:
What I found was that the generator output neutrals were all attached to a threaded stud that is attached to the metal back wall of the control compartment. The jumper from the neutral stud to the ground bar has no effect in isolating neutral from ground because the stud is bonded to all the other metal in the generator & trailer frame!
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Just curious, did you confirm continuity after lifting the jumper? Maybe it's isolated somehow.
 
I did confirm continuity after removing the jumper. I also observed current on the ground with the jumper removed.
It sure seems that they should have landed all the grounds on the threaded stud and the neutrals on an isolated bar (the existing bar with grounds is also mounted to the metal back of the cabinet).
 
LarryFine said:
Since the neutral/ground bond is intact in the building, what would be bad about running the temporary feeder without an EGC, effectively mimicking a utility service?
Click to expand...
The generator frame would (could) be at some potential above the premises grounding system by the amount of the voltage drop on the generator feeder neutral. Whether or not that could pose a hazard would depend on a lot of factors.
 
Electromatic said:
I did confirm continuity after removing the jumper. I also observed current on the ground with the jumper removed.
It sure seems that they should have landed all the grounds on the threaded stud and the neutrals on an isolated bar (the existing bar with grounds is also mounted to the metal back of the cabinet).
Click to expand...
Yeah, that stud does not look insulated, so that’s probably why you still have continuity. You would have to pull the neutrals off and install on an insulated stud.
 
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