generator bonding

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Ponchik

Ponchik

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Location
CA
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Electronologist
I want to make sure I have this understanding. The GFCI on the generator trips when I connect the generator to the house electrical system because the neutral is bonded to the frame and the neutral is bonded at the service.

So in order to have this portable generator to work with the house electrical system is to remove the bonding and ONLY use the generator when it is connected to the house electrical system. Because with a 4 conductor cable if the frame is energized the breaker on the generator will trip because at the service the neutral is bonded.

Am I correct or I am way off?

Thank you for your replies.
 
Sounds like you've got it. If any neutral current flows on the EGC, the GFCI will detect that much current missing from the neutral.
 
Or arrange it so whatever you have for transfer equipment also switches the neutral and assure there is no neutral to ground connection on load side of the transfer equipment.
 
@kwired for this installation it will be too much trouble to do that.

I may modify the generator and install a NC relay so when the generator is being used for the house I can engage the NC relay and the neutral will be disconnected from the frame and when the generator shuts off then it will be reconnected.

Or just buy another generator for portable use.
 
If it’s a Honda, it may have a shunt trip wire that is tied to the breaker. I was able to get my Uncle’s to work by just unplugging the quick connect to the breaker. You could put a switch in line with it as an override.
 
Common place to see separately derived system is with 480/277 systems that require GFP. Neutral needs isolated or the when transferring or else you get undesired current outside the the GFP sensing and it possibly trips. GFCI happens to trip at such low level of current it is even bigger problem if you don't isolate the neutral.
 
It is a Honda unit and ALL of the receptacles are GFCI protected.
@Dsg319 for sure it is not a separately derived system.
 
If you unbond the neutral , then the 120 V GFCI won't see a line to case fault on the load, and OSHA won't allow on a job site. One solution is to make a jumper plug to bond neutral to ground.
I recall some discussion on the code panel when the GFCI requirement was adopted, that the GFCI wouldn't trip if the generator was sitting on wheels and isolated from ground/earth
 
tom baker said:
If you unbond the neutral , then the 120 V GFCI won't see a line to case fault on the load, and OSHA won't allow on a job site. One solution is to make a jumper plug to bond neutral to ground.
I recall some discussion on the code panel when the GFCI requirement was adopted, that the GFCI wouldn't trip if the generator was sitting on wheels and isolated from ground/earth
Click to expand...

If the unbonded generator is connected to the house system via a 4 conductor cable and the grounding conductor is connected to the frame of the generator, why won't the GFCI on the generator respond to a fault?

This will be a good test for me to do.
 
I remember metering a generator that had 60V to ground on the hot and the neutral, difference between the two was 120 of course. Cant remember the brand.
 
edward said:
If the unbonded generator is connected to the house system via a 4 conductor cable and the grounding conductor is connected to the frame of the generator, why won't the GFCI on the generator respond to a fault?

This will be a good test for me to do.
Click to expand...
If you unbond the neutral, then connect it to a house, your neutral will be re-bonded by the house, just in a different location, at the load side of the gfi, which will defeat it because the fault current will go through the sensing CT of the receptacle, instead of around it.
 
edward said:
If the unbonded generator is connected to the house system via a 4 conductor cable and the grounding conductor is connected to the frame of the generator, why won't the GFCI on the generator respond to a fault?

This will be a good test for me to do.
Click to expand...
hillbilly1 said:
If you unbond the neutral, then connect it to a house, your neutral will be re-bonded by the house, just in a different location, at the load side of the gfi, which will defeat it because the fault current will go through the sensing CT of the receptacle, instead of around it.
Click to expand...
What happens depends on how you connect things and whether you switch the neutral with transfer equipment.

If supplying a premises wiring system does the GFCI on generator really mean much? Should be GFCI on any receptacles required to have GFCI protection in 210.8 anyway. If arranged so that fault current would have to return to the source via the GFCI neutral there should be no reason for the GFCI to ever trip.

If used as a stand alone generator with no bonding to the frame it is an ungrounded system, there isn't much for shock hazard on the first ground fault regardless which conductor it occurs on, you just develop a ground reference and a makeshift grounded system. A second ground fault trips GFCI and/or regular overcurrent protection.
 
kwired said:
What happens depends on how you connect things and whether you switch the neutral with transfer equipment.

If supplying a premises wiring system does the GFCI on generator really mean much? Should be GFCI on any receptacles required to have GFCI protection in 210.8 anyway. If arranged so that fault current would have to return to the source via the GFCI neutral there should be no reason for the GFCI to ever trip.

If used as a stand alone generator with no bonding to the frame it is an ungrounded system, there isn't much for shock hazard on the first ground fault regardless which conductor it occurs on, you just develop a ground reference and a makeshift grounded system. A second ground fault trips GFCI and/or regular overcurrent protection.
Click to expand...
Never seen a residential transferswitch switch the neutral. Not saying it’s not out there, but is very rare here in the south, may be common up north, or on the left coast.
 
hillbilly1 said:
Never seen a residential transferswitch switch the neutral. Not saying it’s not out there, but is very rare here in the south, may be common up north, or on the left coast.
Click to expand...
Never seen one either. Most portable gensets I have seen usually don't have frame bonded to neutral. Usually only have GFCI on the 5-15/5-20 receptacles and no GFCI on any 125/250 receptacles they have and is no problem to connect them to a premises wiring system as a non separately derived system. bonding is done in premises wiring and the generator frame becomes bonded via EGC in the supply cord to the house.
 
So today (Thursday) I had the chance to go back and modify the generator. I unbonded the neutral from the generator and connected the generator to the house using a four conductor cord. Turn it on and the GFCI on the generator did not trip. Turned on some house loads and no issue at all. If there is a ground fault in the house or on the housing of the generator the breaker will trip "AS LONG AS" the generator is connected to the house.

However, if the generator is being used out in the field it may be a lethal setup with the frame being floating. So, I am installing a basic push button system with a N/C contactor to unbond the neutral when the generator is connected to the house and as soon as the generator is turned off for storage the N/C contactor will bond the neutral and it will be ready for field use.
 
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