Generator Should I change my PTO generator from Bonded Neutral to Floating Neutral?

[JPCjr]

The bigger the ground wire the closer the gen chassis will be to true house/earth ground. Still, either way on that short run were talking very small difference in potential possible even at full current capability. You could feel it with your tongue if you leave neutral bonded at gen because the ground would be effectively sharing the load with the neutral. Isolate neutral at the gen as youve described.
larry

Touch potential is not the only hazard. Think about what happens when the neutral and ground are not bonded at the generator and there is a ground fault.

 

[stonypass]

Think about what happens when the neutral and ground are not bonded at the generator and there is a ground fault.

The chassis of the generator will be connected to the house ground rod via a 21ft 6ga ground wire in my connection cord, and a 8ft run of 6ga wire from the inlet box to the breaker panel.
Does this not function as a ground and wouldn't this be the path of least resistance if the generator had a wiring fault to ground?

"Neutral floating at generator, neutral not switched at transfer panel. This is a correct configuration. Neutral for the entire system is bonded at the main service panel.
There will be no ground conductor current. Only live lines are switched with a two pole transfer switch."

In this case he's talking about using a two pole transfer switch and I'm going to use an interlock, the transfer switch isolates the generator from power lines as does the interlock in my breaker box.
Electrically they seem the same to me as Neutral is bonded at the panel and Floating at the Generator in both.

I understand the exposure if the generator is used away from the house but inserting the plug pictured in the first post into a 120v outlet will bond Neutral to Ground for those situations.
Perhaps he and I are both wrong however, that's why I've asked the question.

 

[SPYDERLK]

Touch potential is not the only hazard. Think about what happens when the neutral and ground are not bonded at the generator and there is a ground fault.

I am not sure of the terminology, but I think youre posing a case where a hot goes to ground due some load fault. In that case, and all cases where neutral is bonded to the gen chassis there would always be a small charge on the gen if it is not hard grounded. This is because of load sharing in the n/g leads via the neutral/ground bond at the sevice panel. ... Were the N not bonded at gen there would be no charge on its chassis when there was no fault. -- But in the case of a fault there would be charge on the chassis as much as 4x the potential that would exist in the case of the N/G gen bond addressed first. With 6ga wiring at 20 feet we have low numbers. 4 x ~0 = ~ 0 I dont see any danger short of conductor or hookup connection failure. These are within the purview of the installer-operator.
larry

 

[BRBurns]

I am not sure of the terminology, but I think youre posing a case where a hot goes to ground due some load fault. In that case, and all cases where neutral is bonded to the gen chassis there would always be a small charge on the gen if it is not hard grounded. This is because of load sharing in the n/g leads via the neutral/ground bond at the sevice panel. ... Were the N not bonded at gen there would be no charge on its chassis when there was no fault. -- But in the case of a fault there would be charge on the chassis as much as 4x the potential that would exist in the case of the N/G gen bond addressed first. With 6ga wiring at 20 feet we have low numbers. 4 x ~0 = ~ 0 I dont see any danger short of conductor or hookup connection failure. These are within the purview of the installer-operator.
larry

As an electrical engineer, but not willing to look it up, I believe that this is the most correct answer. There is a very slim chance of shock, but it is extremely minimal. I personally would not worry about it.

 

[DarkBlack]

Good debate. I see people debating the pros/cons that I wrote of in my inital post ( #2).

Situation where JpC junior is correct: if you untie the genny ground from it's neutral at the genny, it doesn't matter how big the gauge ground cable to the house is. during a dwelling ground fault. The current that would run the alternate path of the ground wire in the dwelling has no connection to the gen head any more because you removed the tie. It's only path would be to cross to neutral at the service and run back on the neutral wire of your cord. That's not ideal.

Where Spy is correct: If you leave the genny neutral tied to ground, 120 volt loads will be flowing current over the connection cable grounding wire during normal genny operation. This is against nec code, and is not ideal.

 

[BRBurns]

Where Spy is correct: If you leave the genny neutral tied to ground, 120 volt loads will be flowing current over the connection cable grounding wire during normal genny operation. This is against nec code, and is not ideal.

Yes, but if there was a 10 ohm resister in that ground, it would not be flowing any current (still not code). The only reason it would be flowing current is because there is equal resistance. To eliminate the current on the ground you could use a 3 conductor cable 2hots and neutral. And run a separate ground to a separate grounding rod. To me, it's needless.

 

[Victory Pete]

Yes, but if there was a 10 ohm resister in that ground, it would not be flowing any current (still not code). The only reason it would be flowing current is because there is equal resistance. To eliminate the current on the ground you could use a 3 conductor cable 2hots and neutral. And run a separate ground to a separate grounding rod. To me, it's needless.

Current will divide itself up in proportion to the resistance of each parallel path.
You still need the grounding conductor to bond to the service.

VP

 

[BRBurns]

Current will divide itself up in proportion to the resistance of each parallel path.
You still need the grounding conductor to bond to the service.

VP

I didn't mean that a ground was needless. Thanks for noticing my confusing wording. I d that for a temporary setup such as an emergency backup generator. A four conductor cable would be adequate in my book not worrying about separating the neutral from the gen frame. Use your own judgement though and determin wat risks you are willing to take to your own safety vs cost and time.

Oh and the ten ohm comment was assuming a perfect theorectical zero ohm cable. I was meaning to emphasize that the ground would only be carrying current because the resistance is low, not because the circuitry required it to carry load.

 

[JPCjr]

The chassis of the generator will be connected to the house ground rod via a 21ft 6ga ground wire in my connection cord, and a 8ft run of 6ga wire from the inlet box to the breaker panel.
Does this not function as a ground and wouldn't this be the path of least resistance if the generator had a wiring fault to ground? .

No, the grounding electrode (ground rod) has nothing to do with clearning a ground fault.

"Neutral floating at generator, neutral not switched at transfer panel. This is a correct configuration. Neutral for the entire system is bonded at the main service panel.
There will be no ground conductor current. Only live lines are switched with a two pole transfer switch."

In this case he's talking about using a two pole transfer switch and I'm going to use an interlock, the transfer switch isolates the generator from power lines as does the interlock in my breaker box.
Electrically they seem the same to me as Neutral is bonded at the panel and Floating at the Generator in both.

This is correct, but it's assuming that your generator was either manufacutred without the neutral and equipment ground bonded or that there is a removable bonding jumper. Your generator was not manufactured this way and should not be modified. The generator was designed, manufactured, and tested by a third party to ensure that it meets certain safety standards. Modifying the generator changes the system, voids the tests, is prohibited by code (see NEC 90.7, 110.2, and 110.3), and would not be recommended by anyone who understands the hazards involved.

I understand the exposure if the generator is used away from the house but inserting the plug pictured in the first post into a 120v outlet will bond Neutral to Ground for those situations.
Perhaps he and I are both wrong however, that's why I've asked the question.

The purpose of the neutral to equipment ground bond is to conduct fault current. If you have a fault between the ungrounded (hot) and equipment ground, then all of the faul current must flow through the plug/jumper in the photo. I would not trust that and would not be surprised if the circuit breaker never opened during a fault, as the resistance of this configuration is much higher than a solid connection. That is a fire hazard. Also, if there is a bad connection in the plug/jumper and there was a fault, the chasis of the generator would be energized and you could be shocked or electrocuted. The same is true if you separate the neutral and equipment ground and connect the generator to your premises wiring system the way you describe. A bad connection at the plug will result in shock/electrocution hazard and/or fire hazard if you have a fault between the hot and equipment ground.

 

[JPCjr]

The chassis of the generator will be connected to the house ground rod via a 21ft 6ga ground wire in my connection cord, and a 8ft run of 6ga wire from the inlet box to the breaker panel.
Does this not function as a ground and wouldn't this be the path of least resistance if the generator had a wiring fault to ground? .

No, the grounding electrode (ground rod) has nothing to do with clearning a ground fault.

"Neutral floating at generator, neutral not switched at transfer panel. This is a correct configuration. Neutral for the entire system is bonded at the main service panel.
There will be no ground conductor current. Only live lines are switched with a two pole transfer switch."

In this case he's talking about using a two pole transfer switch and I'm going to use an interlock, the transfer switch isolates the generator from power lines as does the interlock in my breaker box.
Electrically they seem the same to me as Neutral is bonded at the panel and Floating at the Generator in both.

This is correct, but it's assuming that your generator was either manufacutred without the neutral and equipment ground bonded or that there is a removable bonding jumper. Your generator was not manufactured this way and should not be modified. The generator was designed, manufactured, and tested by a third party to ensure that it meets certain safety standards. Modifying the generator changes the system, voids the tests, is prohibited by code (see NEC 90.7, 110.2, and 110.3), and would not be recommended by anyone who understands the hazards involved.

I understand the exposure if the generator is used away from the house but inserting the plug pictured in the first post into a 120v outlet will bond Neutral to Ground for those situations.
Perhaps he and I are both wrong however, that's why I've asked the question.

The purpose of the neutral to equipment ground bond is to conduct fault current. If you have a fault between the ungrounded (hot) and equipment ground, then all of the faul current must flow through the plug/jumper in the photo. I would not trust that and would not be surprised if the circuit breaker never opened during a fault, as the resistance of this configuration is much higher than a solid connection. That is a fire hazard. Also, if there is a bad connection in the plug/jumper and there was a fault, the chasis of the generator would be energized and you could be shocked or electrocuted. The same is true if you separate the neutral and equipment ground and connect the generator to your premises wiring system the way you describe. A bad connection at the plug will result in shock/electrocution hazard and/or fire hazard if you have a fault between the hot and equipment ground.