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

[stonypass]

I just purchased a new to me 12KW PTO Generator for emergency home power.
I'm planning on installing a 50a 240v breaker and an interlock kit for economy and so I can power any circuit (obviously not all at the same time).

There is a sticker on the top of the generator that states "Neutral Bonded to Chassis" and after reading here: Home generator installation I'm wondering if this should be changed to "Floating Neutral" for best safety. From the website, I would currently have setup #3 but if I changed my generator to "Floating Neutral" would have setup #2.

"There are four possible ground / neutral bond and transfer panel configurations.

1. Neutral bonded at generator, neutral switched at transfer panel. This is a correct configuration. Neutral for backup circuits will be isolated at the transfer panel and bonded within the generator. There will be no ground conductor current. This requires a three pole transfer switch.
2. 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.
3. Neutral bonded at generator, neutral not switched at transfer panel. This seems to be the most common connection technique based on my research. Unfortunately it is not correct. Neutral will be connected to ground at the main panel and at the generator. Neutral current flow will flow along the ground conductor and through the generator chassis. This creates a potential shock hazard as the chassis becomes part of the current carrying circuit. The easiest way to fix the problem is to use a floating neutral generator or make the required changes to the generator internal wiring.
4. Neutral floating at generator, neutral switched at transfer panel. The neutral conductor has no ground reference. The neutral should be bonded within the generator or the transfer switch rewired to not switch the neutral conductor."


The pic with the capacitors shows under the Top Cover and the other is the Back Side of the panel with the Outlets and Breakers.
Under the top cover, the two Black wires at the top posts and the Large White one on the Bottom right posts all go to the Breaker Panel. There is a green wire attached to the Lower Left post that's attached to the Genset Chassis. (All others go to the generator)
On the back of the Breaker panel the white Neutral wires are bonded to ground at the bottom middle of the panel which is the back side of a ground lug for connecting to a ground rod.

I'm not a generator expert but it seems to me if I removed the green wire from the lower left post under the top cover, and removed the Neutral wires from the Ground lug on the breaker panel then tied them together separately I would have a floating Neutral configuration on my generator. I don't plan on using this generator to power saws and drills when not attached to my home, but if I do would use the plug shown during these times to bond Neutral to the Chassis temporarily.

I would like some opinions on whether or not I should make this change.
If the answer is yes, will the method I have described work properly to give me a Floating Neutral?

Thanks for all advice

 

[DarkBlack]

That's a good question, almost like a brain teaser to post a tech correct answer.
What makes it seem like a puzzle is there are 2 unknowns that make the correct answer hard to come to. The first is, are you looking for greatest electrical saftey while in the house/structure, or greatest safety while near/at the generator. And second, the safest solution depends on if you are going to insure a good generator frame connection to earth with a rod, or will it be left isolated on wheels and painted steel?

 

[stonypass]

I'm not an electrician, but my understanding is that while connected to my house with a four wire connection a ground rod is not desired since this creates two separate grounds that might be at different potential. A ground rod should be used when a generator is run in standalone mode (but most probably aren't). I would think my greatest risk in powering my home in an emergency situation is while hooking up the generator outside as the ground is likely to be wet with rain, snow or ice.

In answer to your question, I'm trying to find out the best/safest way to wire up the generator for emergency home power. The link I provided seems to indicate the generator Neutral should be changed for my application.
I would also like to know how to stay safe if I operate the generator in standalone mode as this could happen as well. Although I purchased this generator used I did download the manual for it but find haven't found it to be very educating in terms of operation.

 

[DarkBlack]

Yes and no. There are already 2 ground points and many nearby( neighbors). At your service entrance for one, and at the pole ground. When under grid power a fault can make it's way back to the grid through a multitude of paths. That's why your first post is such a brain teaser. The "best" correct "safety" answer depends on the circumstance. What's best saftey for a structure fault is probably not the best setup for best saftey while at the genny refueling it in the snow. That's why I asked for your preference. Nobody opens grounds when running gennies so you have to factor in that all these return paths are still possible.

 

[SPYDERLK]

I just purchased a new to me 12KW PTO Generator for emergency home power.
I'm planning on installing a 50a 240v breaker and an interlock kit for economy and so I can power any circuit (obviously not all at the same time).

There is a sticker on the top of the generator that states "Neutral Bonded to Chassis" and after reading here: Home generator installation I'm wondering if this should be changed to "Floating Neutral" for best safety. From the website, I would currently have setup #3 but if I changed my generator to "Floating Neutral" would have setup #2.

"There are four possible ground / neutral bond and transfer panel configurations.

1. Neutral bonded at generator, neutral switched at transfer panel. This is a correct configuration. Neutral for backup circuits will be isolated at the transfer panel and bonded within the generator. There will be no ground conductor current. This requires a three pole transfer switch.
2. 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.
3. Neutral bonded at generator, neutral not switched at transfer panel. This seems to be the most common connection technique based on my research. Unfortunately it is not correct. Neutral will be connected to ground at the main panel and at the generator. Neutral current flow will flow along the ground conductor and through the generator chassis. This creates a potential shock hazard as the chassis becomes part of the current carrying circuit. The easiest way to fix the problem is to use a floating neutral generator or make the required changes to the generator internal wiring.
4. Neutral floating at generator, neutral switched at transfer panel. The neutral conductor has no ground reference. The neutral should be bonded within the generator or the transfer switch rewired to not switch the neutral conductor."


The pic with the capacitors shows under the Top Cover and the other is the Back Side of the panel with the Outlets and Breakers.
Under the top cover, the two Black wires at the top posts and the Large White one on the Bottom right posts all go to the Breaker Panel. There is a green wire attached to the Lower Left post that's attached to the Genset Chassis. (All others go to the generator)
On the back of the Breaker panel the white Neutral wires are bonded to ground at the bottom middle of the panel which is the back side of a ground lug for connecting to a ground rod.

I'm not a generator expert but it seems to me if I removed the green wire from the lower left post under the top cover, and removed the Neutral wires from the Ground lug on the breaker panel then tied them together separately I would have a floating Neutral configuration on my generator. I don't plan on using this generator to power saws and drills when not attached to my home, but if I do would use the plug shown during these times to bond Neutral to the Chassis temporarily.

I would like some opinions on whether or not I should make this change.
If the answer is yes, will the method I have described work properly to give me a Floating Neutral?

Thanks for all advice

I see wt/neutral bonded to chassis in both pic if you trace that grn wire. It should NOT be - unless the gen is grounded. The shown config will result in a charge on the gen when powering your home service. It will be lo voltage, but maybe enuf to feel when the load is heavy. Remove/disconnect the whites from chassis ground and this wont happen.
larry

 

[stonypass]

I see wt/neutral bonded to chassis in both pic if you trace that grn wire. It should NOT be - unless the gen is grounded. Remove/disconnect the whites from chassis ground and this wont happen.

That is what I'm thinking as well, the current configuration would be fine for running while not connected to my house if the Chassis was grounded. Hooked to the house, I think I should remove the green wire from under the top cover and separate the whites from the ground lug on the connection panel.

 

[SPYDERLK]

I think that would do it.

 

[schmism]

Hooked to the house, I think I should remove the green wire from under the top cover and separate the whites from the ground lug on the connection panel.

I would agree with the above.

The only other thing i would do is ground the chassis of the generator to (dirt)ground with a ground rod. (if close enough to the meter location you could tie to that ground rod) this prevents the chassis from becoming energized if a short from hot to the chassis is made and then you walk up and touch the chassis thus completing the circuit to ground and getting shocked. (note after the above changes a short to neutral is bled off at the main panel were neutral and ground are common. hopefully causing a circuit breaker to trip on the genset)

second note: it starts to get a bit confusing with mulitipul ground rods in the same circuit as you have the possiblity of creating "ground loops" of various potential. in systems that need a high degree of ground quality, mulipull ground points must also be tied together (usually with bare copper wire underground also) generally speaking for most homeowner electrical systems dont need to worry about such things as the voltages are low and cause little physical risk. Although if your a ham radio operator or the like you are likely much more concerned about ground loops and noise but then again, if you were you wouldnt be asking such a question on a tractor forum

 

[stonypass]

On the back of the connection panel all the green wires are tied to a ground lug, the panel is also bolted to the generator chassis.
To connect the generator to the house, I'll be using a 6ga 4wire cable that will plug into a generator inlet box on the side of my garage.
The inlet box is within 6 feet or so of the main service entrance where there is a ground rod, but am I not already tied to it via the ground wire on my connection cable?

 

[stonypass]

When I add a 240v 50a breaker for my generator inlet, is there any reason this can't be added at the bottom of the box if there are already open spaces?
Usually the larger one's are at the top but I didn't know if there was an electrical reason for this.

 

[schmism]

Usually the larger one's are at the top but I didn't know if there was an electrical reason for this.

If your backfeeding a standard breaker then generally they are positioned as close to the main breaker as possible to facilitate a lockout/interlock device so that neither breakers can be on at the same time. (the only "legal" way to backfeed a panel)

 

[stonypass]

Not sure what I was thinking, I am planning on using an interlock so I'll have to move the breakers on the right side down to make room for the Generator inlet at the top right.

When the house was built in 1996 however, I ran a 2-2-4 line to the barn and put the breakers for it at the bottom left side of the panel since there was open space there. Any reason to move it up as a part of this install?

 

[SPYDERLK]

Not sure what I was thinking, I am planning on using an interlock so I'll have to move the breakers on the right side down to make room for the Generator inlet at the top right.

When the house was built in 1996 however, I ran a 2-2-4 line to the barn and put the breakers for it at the bottom left side of the panel since there was open space there. Any reason to move it up as a part of this install?

Not really. The buss bars in the service panel are usually pretty hefty. Voltage will be higher closer to the top, esp when under heavy loading. Were talkin only a couple hundred millivolts max tho.
larry

 

[JPCjr]

I think you may be getting some bad information here. You should NOT make the changes you suggested. Your generator is configured as a separately derived system and it is not field reconfigurable. Therefore, the only safe way to connect your generator to your premises wiring system is through a transfer switch that switches the neutral. Three pole transfer switches are available. If you modify your generator, you are violating NEC articles 90.7, 110.2, and 110.3.

Portable generators that can be configured as a separately derived system or a non-separately derived system are also available. In these cases, a system bonding jumber is installed for a separately derived system or removed for a non-separately derived system. If the system bonding jumper is removed, the neutral from the premises wiring system must be solidly connected to the generator. A plug and receptacle at the generator is not a solid connection.

One of the problems with making the modifications you are suggesting is that the fault current path during an undgrounded (hot) to equipment grounding conductor (ground) fault between the premises wiring system and generator is not directly back to the source, as it should be. Instead, the fault current would need to flow through the premises wiring system main bonding jumper and back to the generator through the neutral. Also, if you were to ever use the generator as described with the plug in the first picture, the same is true. The fault current would be flowing through the plug. In both of these cases if you ever had a fault the circuit breaker may never trip.

 

[Victory Pete]

I think you may be getting some bad information here. You should NOT make the changes you suggested. Your generator is configured as a separately derived system and it is not field reconfigurable. Therefore, the only safe way to connect your generator to your premises wiring system is through a transfer switch that switches the neutral. Three pole transfer switches are available. If you modify your generator, you are violating NEC articles 90.7, 110.2, and 110.3.

Portable generators that can be configured as a separately derived system or a non-separately derived system are also available. In these cases, a system bonding jumber is installed for a separately derived system or removed for a non-separately derived system. If the system bonding jumper is removed, the neutral from the premises wiring system must be solidly connected to the generator. A plug and receptacle at the generator is not a solid connection.

One of the problems with making the modifications you are suggesting is that the fault current path during an undgrounded (hot) to equipment grounding conductor (ground) fault between the premises wiring system and generator is not directly back to the source, as it should be. Instead, the fault current would need to flow through the premises wiring system main bonding jumper and back to the generator through the neutral. Also, if you were to ever use the generator as described with the plug in the first picture, the same is true. The fault current would be flowing through the plug. In both of these cases if you ever had a fault the circuit breaker may never trip.

As a licensed electrician I agree. Grounding can be very confusing. You should check with your LAHJ (Inspector) before you do anything. Have a look here:Grounding and Bonding of Separately Derived AC Systems | NEC content from Electrical Construction and Maintenance (EC and M) Magazine

VP

 

[DarkBlack]

Shut of you main breaker,Tie in a suicide cord, backfeed a 240v outlet,start her up and be good to go.

 

[TMB1320]

Bonding the gen chassis is for protection against the genny developing a fault where some segment
Of the windings shorts to the iron core. The hot chassis results if it were not bonded. And for the ground loop problem, definitely disconnect the neutral from the mains provided your house neutral
Is bonded to a ground rod, or municipal copper water pipe to the house.

 

[stonypass]

As previously stated, I will be using an interlock and a 50a double pole breaker due to the limitations imposed by a transfer switch.

In my breaker box neutrals and grounds are bonded to a common bus and there is a ground rod on the other side of the wall.
The question is whether or not to leave neutral bonded to ground on the generator, or to isolate neutral from ground on the generator?

Also the cord that came with my generator is 22ft long and 6ga for all four wires.
A nearby hardware store sells 6/3 with ground in a sheath but the ground is 10ga, should the ground be 6ga as well?

I live in a rural area where inspections will not be required, but I'm wondering if I called three electricians would all tell me the same thing?

 

[SPYDERLK]

As previously stated, I will be using an interlock and a 50a double pole breaker due to the limitations imposed by a transfer switch.

In my breaker box neutrals and grounds are bonded to a common bus and there is a ground rod on the other side of the wall.
The question is whether or not to leave neutral bonded to ground on the generator, or to isolate neutral from ground on the generator?

Also the cord that came with my generator is 22ft long and 6ga for all four wires.
A nearby hardware store sells 6/3 with ground in a sheath but the ground is 10ga, should the ground be 6ga as well?

I live in a rural area where inspections will not be required, but I'm wondering if I called three electricians would all tell me the same thing?

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

 

[JPCjr]

You're asking what is the better of two bad choices. Neither option is code compliant or safe. If you want a safe installation follow the code. I'll be glad to help you if you have questions about how to do that. You may also want to check here: Mike Holt's Forum