manual transfer switch tripping generator breaker

[journeyman0217]

hey guys,
ran into an issue today that has me stumped. I just got done installing a 10 circuit 30amp manual transfer switch for a customer. the 120/240 30amp outlet on the gen. is gfi protected. at the end of my install I went to test operation in generator mode. I went down and turned all of the transfer switches in the "off" position, when I went to plug the power inlet cord in it immediately tripped the breaker and the gfci on the gen. being that the transfer switches were in the off position I assumed the was an issue with the cord or wiring from the power inlet to the transfer switch. everything looked good visually. to narrow down the possible problem I disconnect the feeder wire from the generator to the transfer switch. fired up the generator, plugged in the cord to the power inlet. this time the breaker held. I went down and made sure I had correct voltage between conductors. everything was good. with the gen off i connected the ground and neutral back up, both hots are disconnected at this put, fired the gen back up and go to plug the gen cord back in and it popped the breaker and gfi on gen again. i was wondering why the gfi was popping too, i threw my amp meter on the neutral to see if i had any stray current coming back on the neutral to the gen and read 0. next thing i threw the main breaker off to the house, fired the gen up again, and when i hooked the cord up it popped the gfi and breaker again! with the main breaker off i checked amperage on my two hots and read zero, threw it on the neutral and read .08 amps? figured that was the problem, some stray current coming back on the neutral to gen but when i stick amp meter on the neutral from the gen feeder wire it reads 0. also with the main breaker back on i read 2.9 amps on L1 and 1.9 amps on L2, neutral should have 1 amp but it reads 2.5 amps! went and check out service taps for possible loose neutral connection. visually looks good but i have to go back with a ladder. this one has me stumped because if the was somehow stray current on the neutral wouldn't this trip all the gfci in the house? i at a lose on this one......any ideas on what this issue could be? also customer is going to borrow another gen to eliminate the gen as being the issue.

 

[George Stolz]

Unless you're using a three pole transfer switch, the main bonding jumper in the service is tripping the GFCI on the generator.

 

[journeyman0217]

im a little confused....can u explain y? with no current drawl on any conductor i just don't understand how

 

[DrSparks]

You let the smoke out

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[journeyman0217]

"ground loop"....but if there is no current going through any conductors wouldn't the ground and neutral just act as a parallel conductor until there is current flow then current would leak out onto the ground causes gfi to trip

 

[Little Bill]

im a little confused....can u explain y? with no current drawl on any conductor i just don't understand how

The generator neutral is bonded to ground, the main service is also bonded to ground. Only (legal/compliant) way to keep the gen. GFCI from tripping is to do as George said and use a 3-pole transfer switch that disconnects the neutral.

 

[LarryFine]

To explain further, most modern GFCIs will trip if the neutral and EGC are connected together after the device. The white and green wires from the transfer switch are normally both landed on the neutral bus of the house panel. This will trip the generator's GFCI any time it's running, even with no load.

They're suggesting that, when you're running the 10 circuits on the generator, the neutral of the transfer switch be lifted from the neutral of the house panel, which will break the parallel connection between the white and green wires. The problem is the 10 individual switches in the generator panel.

With that type of transfer switch (more accurately, 10 transfer switches (ignoring any 2-pole handle ties (presuming I'm correct about the type of transfer switch you installed))), the 10 circuits' neutrals remain on the house panel's neutral bus, so they can't be switched nor isolated from the house panel.

In my opinion, your only option is to lift the neutral-to-ground connection inside the generator, making it less than safe for any use other than when connected to this house and transfer switch setup. Or, find a way to install a switch to make and break this connection when needed for greater versatility.

 

[Jamesco]

To explain further, most modern GFCIs will trip if the neutral and EGC are connected together after the device. The white and green wires from the transfer switch are normally both landed on the neutral bus of the house panel. This will trip the generator's GFCI any time it's running, even with no load.

They're suggesting that, when you're running the 10 circuits on the generator, the neutral of the transfer switch be lifted from the neutral of the house panel, which will break the parallel connection between the white and green wires. The problem is the 10 individual switches in the generator panel.

With that type of transfer switch (more accurately, 10 transfer switches (ignoring any 2-pole handle ties (presuming I'm correct about the type of transfer switch you installed))), the 10 circuits' neutrals remain on the house panel's neutral bus, so they can't be switched nor isolated from the house panel.

In my opinion, your only option is to lift the neutral-to-ground connection inside the generator, making it less than safe for any use other than when connected to this house and transfer switch setup. Or, find a way to install a switch to make and break this connection when needed for greater versatility.

In my opinion, your only option is to lift the neutral-to-ground connection inside the generator, making it less than safe for any use other than when connected to this house and transfer switch setup. Or, find a way to install a switch to make and break this connection when needed for greater versatility.

Or how about using only the 2 hots and neut from the generator receptacle to the MTS. No EGC ground wire. He doesn't need the EGC when the generator is connected to the house. The house service neut is grounded/earthed.

What do you think?

 

[George Stolz]

:blink:

 

[George Stolz]

Where is GFCI protection required for this installation?

Edit to add before bed: if it is required, then removing the bonding jumper in the generator (relying on the one in the service) is the compliant fix I see.

 

[Jamesco]

Where is GFCI protection required for this installation?

Edit to add before bed: if it is required, then removing the bonding jumper in the generator (relying on the one in the service) is the compliant fix I see.

My understanding is it's a portable generator. Lifting the neutral will be dangerous if the generator is used as portable generator. The generator output will be wired as an Isolated Power System. The GFCI protection will be worthless. A GFCI will not operate, as designed, when connected to an Isolated Power System.



.

 

[electrofelon]

My understanding is it's a portable generator. Lifting the neutral will be dangerous if the generator is used as portable generator. The generator output will be wired as an Isolated Power System. The GFCI will be worthless.

It could be argued that if the GFCI wont trip, than there is enough isolation such that a line to ground shock couldnt happen.

 

[Jamesco]

It could be argued that if the GFCI wont trip, than there is enough isolation such that a line to ground shock couldnt happen.

True.

But would it be safe to use a portable generator where the neutral is floating, not bonded to the metal frame. 3 ungrounded conductors.

What happens if????
Say one of the outer leads of the 240V winding goes/faults to generator case/frame. It's now a grounded conductor. Will the generator continue to operate? The voltage from the floating neutral to ECG/frame of the generator will measure 120Vac Nominal. The other ungrounded conductor of the 240V winding to EGC/ frame will measure 240V nominal. Problem? Maybe if,.....

I would not lift neutral from a portable generator that may be used as portable generator. The OP would be leaving himself wide open for a lawsuit in the event someone seriously got shocked or electrocuted.

Tell me what's wrong if the OP does not use the EGC from the generator to the house MTS? Remember a cord and plug, plugs into a twistlok 120/240V 4 wire receptacle on the portable generator that feeds generator power to the MTS. (I assume it's a twistlok)


.

 

[LarryFine]

Duplicate.

 

[LarryFine]

My understanding is it's a portable generator. Lifting the neutral will be dangerous if the generator is used as portable generator. The generator output will be wired as an Isolated Power System. The GFCI protection will be worthless. A GFCI will not operate, as designed, when connected to an Isolated Power System.

That's why I suggested a switch.

 

[GoldDigger]

FWIW, the reason that a GFCI breaker can trip on a downstream ground to neutral connection with no load current drawn is that in addition to the differential toroid looking for unbalanced current there is an additional toroid that injects a voltage on the downstream neutral relative to the EGC and looks for current.

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[journeyman0217]

Thank you golddigger, that's what I didn't understand.

FWIW, the reason that a GFCI breaker can trip on a downstream ground to neutral connection with no load current drawn is that in addition to the differential toroid looking for unbalanced current there is an additional toroid that injects a voltage on the downstream neutral relative to the EGC and looks for current.

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[journeyman0217]

Aren't there portable generators out there with a floating neutral? Wouldn't they be unsafe for portable use? If the generator had a bonded neutral but no gfci protection the breaker on the gen wouldn't trip correct? It's the gfi that sensing the ground loop issue...

 

[electrofelon]

True.

But would it be safe to use a portable generator where the neutral is floating, not bonded to the metal frame. 3 ungrounded conductors.

What happens if????
Say one of the outer leads of the 240V winding goes/faults to generator case/frame. It's now a grounded conductor. Will the generator continue to operate? The voltage from the floating neutral to ECG/frame of the generator will measure 120Vac Nominal. The other ungrounded conductor of the 240V winding to EGC/ frame will measure 240V nominal. Problem? Maybe if,.....

I would not lift neutral from a portable generator that may be used as portable generator. The OP would be leaving himself wide open for a lawsuit in the event someone seriously got shocked or electrocuted.

Tell me what's wrong if the OP does not use the EGC from the generator to the house MTS? Remember a cord and plug, plugs into a twistlok 120/240V 4 wire receptacle on the portable generator that feeds generator power to the MTS. (I assume it's a twistlok)


.

Aren't there portable generators out there with a floating neutral? Wouldn't they be unsafe for portable use? If the generator had a bonded neutral but no gfci protection the breaker on the gen wouldn't trip correct? It's the gfi that sensing the ground loop issue...

There was a discussion on here a short time ago about un bonded generators. It seems they are out there but the vast majority of small consumer generators are bonded. I know this isnt what the NEC says, but I feel a unbonded generator is safer for portable use. Here in the US we are obsessed with grounding things. I always say system grounding isnt about "safety" or "safer", its just a system topology. Each has positives and negatives. For the portable generator case, I think floating is safer.

 

[kwired]

It could be argued that if the GFCI wont trip, than there is enough isolation such that a line to ground shock couldnt happen.

I won't argue, I will insist that is how it would be. You need a fault on a second line to have a shock hazard - but when that happens the GFCI will trip.

True.

But would it be safe to use a portable generator where the neutral is floating, not bonded to the metal frame. 3 ungrounded conductors.

What happens if????
Say one of the outer leads of the 240V winding goes/faults to generator case/frame. It's now a grounded conductor. Will the generator continue to operate? The voltage from the floating neutral to ECG/frame of the generator will measure 120Vac Nominal. The other ungrounded conductor of the 240V winding to EGC/ frame will measure 240V nominal. Problem? Maybe if,.....

I would not lift neutral from a portable generator that may be used as portable generator. The OP would be leaving himself wide open for a lawsuit in the event someone seriously got shocked or electrocuted.

Tell me what's wrong if the OP does not use the EGC from the generator to the house MTS? Remember a cord and plug, plugs into a twistlok 120/240V 4 wire receptacle on the portable generator that feeds generator power to the MTS. (I assume it's a twistlok)


.

Aren't there portable generators out there with a floating neutral? Wouldn't they be unsafe for portable use? If the generator had a bonded neutral but no gfci protection the breaker on the gen wouldn't trip correct? It's the gfi that sensing the ground loop issue...

Many portable generators out there with a floating neutral.

I think they kind of keep disagreeing on whether it is better to bond them to neutral or not. Depending on age of the unit you will see most of the same age are all either bonded or not bonded. Seems the more recent trend is they are usually bonded. About 10-15 years ago most were not bonded.