Neutral Bonded Generator with Meter Mounted Transfer Switch

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spicywire

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Location
Georgia
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Engineer
Hi everyone, formerly low voltage/digital design guy looking for some insight. I have a question related to connecting a neutral bonded generator with GFCI to a meter mounted transfer switch.

The generator I have is configured to be a separately derived system in order to be OSHA compliant. I would like to use this same generator as a backup power source for my home in the event of power outages. However, my transfer switch is meter mounted, and has the neutral and ground connections from the generator bonded. This transfer switch does not switch neutral.

I see that in this situation, the neutral to frame connection must be removed at the generator in order to prevent creating a parallel path for neutral current to flow. Additionally, since the generator is connected to preexisting wiring, it would utilize the neutral/ground bond and EGC of the home's wiring. Under normal circumstances, disconnecting the neutral bond within the generator would be the easy and typically recommended solution. Unfortunately, I cannot modify this generator's neutral bond. Additionally, the generator has a GFCI, making it unusable with my transfer switch with its current wiring setup.

In this situation, would it be possible to remove the ground connection between the generator and transfer switch and still have a code compliant and safe system?
I am trying to work my way through relevant codes/standards (NEC, UL), as well as normal operational and fault conditions, but am a little uncertain of how viable/safe this solution would be.

Under normal operating conditions, I believe this would function properly. Line 1, line 2, and neutral are connected between the generator and transfer switch. Neutral and ground (generator chassis) are bonded internally. The chassis would be at the same potential as neutral.
However, fault conditions have me concerned. In a line to chassis fault, there would be the possibility of current flowing between line, chassis, and back to neutral for an undetermined amount of time. Ideally, any internal current limiting protections would trip, but I do not know specifically how long this would take to trigger.

Looking forward to any advice on this situation. Thanks!

Summary:
Generator configured as neutral bonded and has GFCI.
Transfer switch is meter mounted and has neutral and ground from generator inlet bonded, as it is the first means of disconnect.
Unable to modify generator or transfer switch.
Looking to modify connection between generator and transfer switch to allow for proper operation as home backup system.
 
Unless you unbond the neutral on the generator or set up your transfer switch as a separately derived system you are always going to trip the generator GFCI. The simple solution is to use a couple of extension cords for the refrigerator and a lamp out to the generator and wait for the power to come back on.
 
ActionDave said:
Unless you unbond the neutral on the generator or set up your transfer switch as a separately derived system you are always going to trip the generator GFCI. The simple solution is to use a couple of extension cords for the refrigerator and a lamp out to the generator and wait for the power to come back on.
Click to expand...
How would the GFCI be tripped if the ground connection from the generator to the transfer switch was removed? The issue, at least from what I can tell, in the original setup is that there is a parallel path back to the generator neutral through the neutral wire and the parallel ground wire from the TS to the generator ground, then back to neutral through the internal bonding. If the ground wire was disconnected from the cable between the generator and transfer switch only, wouldn't this remove the parallel path, making it so all current flowing out from L1 and L2 return through neutral?
 
I have seen a generator on a welder's truck with a switch added for the neutral bond, I think it was for this purpose.
 
spicywire said:
Hi everyone, formerly low voltage/digital design guy looking for some insight. I have a question related to connecting a neutral bonded generator with GFCI to a meter mounted transfer switch.

The generator I have is configured to be a separately derived system in order to be OSHA compliant. I would like to use this same generator as a backup power source for my home in the event of power outages. However, my transfer switch is meter mounted, and has the neutral and ground connections from the generator bonded. This transfer switch does not switch neutral.

I see that in this situation, the neutral to frame connection must be removed at the generator in order to prevent creating a parallel path for neutral current to flow. Additionally, since the generator is connected to preexisting wiring, it would utilize the neutral/ground bond and EGC of the home's wiring. Under normal circumstances, disconnecting the neutral bond within the generator would be the easy and typically recommended solution. Unfortunately, I cannot modify this generator's neutral bond. Additionally, the generator has a GFCI, making it unusable with my transfer switch with its current wiring setup.

In this situation, would it be possible to remove the ground connection between the generator and transfer switch and still have a code compliant and safe system?
I am trying to work my way through relevant codes/standards (NEC, UL), as well as normal operational and fault conditions, but am a little uncertain of how viable/safe this solution would be.

Under normal operating conditions, I believe this would function properly. Line 1, line 2, and neutral are connected between the generator and transfer switch. Neutral and ground (generator chassis) are bonded internally. The chassis would be at the same potential as neutral.
However, fault conditions have me concerned. In a line to chassis fault, there would be the possibility of current flowing between line, chassis, and back to neutral for an undetermined amount of time. Ideally, any internal current limiting protections would trip, but I do not know specifically how long this would take to trigger.

Looking forward to any advice on this situation. Thanks!

Summary:
Generator configured as neutral bonded and has GFCI.
Transfer switch is meter mounted and has neutral and ground from generator inlet bonded, as it is the first means of disconnect.
Unable to modify generator or transfer switch.
Looking to modify connection between generator and transfer switch to allow for proper operation as home backup system.
Click to expand...
Do you have make and model of your generator?
Maybe someone can find a schematic of the wiring and share how to remove the bond without disconnecting the equipment ground.
 
qcroanoke said:
Do you have make and model of your generator?
Maybe someone can find a schematic of the wiring and share how to remove the bond without disconnecting the equipment ground.
Click to expand...
I can't get into the specific details. I am not allowed to disconnect the neutral bond within the source.
 
spicywire said:
I can't get into the specific details. I am not allowed to disconnect the neutral bond within the source.
Click to expand...
Ok. You spoke of taking the equipment ground loose between the generator and Transfer switch
I would not do that.
If you are not allowed to take the bond loose you're probably not allowed to disconnect the equipment ground.
Only option you have is post#2.
 
qcroanoke said:
Ok. You spoke of taking the equipment ground loose between the generator and Transfer switch
I would not do that.
If you are not allowed to take the bond loose you're probably not allowed to disconnect the equipment ground.
Only option you have is post#2.
Click to expand...
Given the circumstances, I was looking into whether modifying the connection between the generator and transfer switch would work. Regarding post #2, I assume that leakage current would cause the GFCI to trip, but they didn't get into specifics of why the GFCI would still trip in this setup.

Beyond that, I still have some concerns over safety, so I'll look into other ways to make this work. Might just be that what I'm looking to do isn't possible, and a different generator is needed.

Thanks for your responses!
 
Not sure if they make a meter transfer that will switch the neutral, but if you have a gen set that is N/G bonded that cannot be changed, then you would need to switch the neutral at the transfer and create a SDS setup, to be code compliant. (not that I haven't seen or heard of this not be complied with.)
 
I ordered this almost 3 years ago, don't know if Reliance still has them.

Subject: Reliance Panels

The XRC Series was discontinued a while ago – alternative/replacement is the XRK Series, delivery is estimated at 2-3 weeks. There will be freight charges. Let me know which one you are interested in.
 XRK1005CR $380
 XRK1005DR $344
 No replacement but closest option would be XRK1006DR $344

For use with:
• GFI-equipped generators
• Bonded neutral generators
• Separately-derived systems
The sequentially-switched neutral means you can switch between a portable generator and utility power without the danger of sending 240V current to a 120V circuit.

The New Reliance Panel/Link X Series is a double-pole manual transfer switch with an exclusive third-pole for the neutral that switches sequentially. The X Series is perfect for use with generators having GFCI protected outlets, bonded neutral generators and installations requiring a separately-derived system.
On GFI protected generators, the X Series will prevent a ground fault which will, in turn, prevent the circuit breakers on the generator from nuisance tripping.
The XRC Series has 10 branch circuit spaces and will allow up to 18 circuits with the use of tandem breakers. The XRR Series allows for 26/36 branch circuits and is available in indoor and outdoor enclosures. Options include a selection of watt meters, for balancing generator load, and flanged inlets for direct generator connection where permitted.

How does the X Series work?
The X Series’ exclusive, patent-pending switching mechanism will break the two hot legs of the circuit, in either direction, before the neutral is broken. It will then close the neutral before the two hot legs close. This prevents destructive 240V current from momentarily powering the 120V circuits and damaging inductive motors and sensitive electronics.
 
ActionDave said:
Unless you unbond the neutral on the generator or set up your transfer switch as a separately derived system you are always going to trip the generator GFCI. The simple solution is to use a couple of extension cords for the refrigerator and a lamp out to the generator and wait for the power to come back on.
Click to expand...
Not only simple, but it avoids issues with home owners insurance and if you are using a hybrid vehicle for your generator, your auto insurance. The code gives the insurance companies a perfectly good reason to deny any claims related to loss of life or property
 
icaser, please update your profile information to include your occupation.
 
icaser said:
Not only simple, but it avoids issues with home owners insurance and if you are using a hybrid vehicle for your generator, your auto insurance. The code gives the insurance companies a perfectly good reason to deny any claims related to loss of life or property
Click to expand...
You and Ramsy should start a club!
 
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