During a recent power outage a client contacted us claiming his 8kw generator w/ gfci protection was going into fault while he attempted to connect it to his 30 amp inlet to power his transfer switch.I suggested that we isolate the grounding conductor from the neutral which were under one terminal and drive a ground rod and connect a #6 cu. wire to it. Any comments. Thanks
generator faulting
- Thread starter Mr. M
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ceb58
Senior Member
- Location
- Raeford, NC
It was faulting because of the GFCI protection because of the N-G bond on the house. The transfer switch for these type generators should switch the neutral. Driving a ground rod will only make you tired.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
I agree, to keep the UL listing intact, change the transfer switch to one that also switches the neutral.
jwelectric
Senior Member
- Location
- North Carolina
Don't get mad. The answer is no.
ceb58
Senior Member
- Location
- Raeford, NC
Look at 250.34 (A). No RO required :happyno:
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
The problem as was said is if you are trying to transfer the whole house and there is a neutral to ground bond on the load side of the transfer switch the GFCI in the generator will treat it as a ground fault, just switching the neutral will not prevent this as with isolating the neutral to ground bond at the generator as you are still on the load side of the generators GFCI, also isolating the neutral to ground bond at the generator without providing a equipment grounding conductor will not provide a fault current path if a fault were to occur in the cable between the transfer switch and the generator this would be a very dangerous installation as it could present a shock hazard.
A ground rod can not take the place of a equipment grounding conductor as the Earth can not provide a low enough impedance path to allow the opening of over current protection if a fault was to occur, never do this.
Many newer portable generators now have GFCI protection even on the twist-loc and this stops them from being used as in the above installation.
To use a GFCI protected generator to supply premise wiring will take putting the circuits to be supplied into a separate sub-panel with the transfer switch between the main panel and this sub panel, and a 3-pole transfer switch to maintain the neutral to ground isolation in the main panel.
A 4-wire cord also will have to be used to allow the neutral to ground bond at the generator to be maintained for a fault current path.
Another option is to install a new service disconnect between the meter and the existing panel then separate the grounding and neutrals in the existing panel and move the GEC's to the new disconnect, then put a 3-pole transfer switch between the new disconnect and panel.
The last option and sometimes the least costly is to return the portable generator and get one designed to supply premise wiring that doesn't have GFCI protection on the output to the house.
Ever since the new requirements for GFCI protection on all outlets on portable generators was put into the manufactures requirements, it made using portable generators much harder to be used as a backup power source for premise wiring systems because of the neutral to ground bond required at every service, so making sure the correct equipment is used is a must.
I have heard that there are still some portable generators out there that still don't have the GFCI protection on the twist-loc receptacle, but since I only install generators that are design for premise wiring backup I couldn't tell you which brands they are.
Sorry for the bad news
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
sorry but just switching the neutral will not fix this as there will still be a neutral to ground bond in the main panel, any neutral to ground bond on the load side of any GFCI device will still trip the GFCI, lifting the neutral to ground bond in the generator will also not fix it, remember you don't even have to have a ground on the line side of a GFCI for the GFCI to still trip if there is a load side neutral to ground bond.
The only method is keeping the grounds and neutral separate anytime you are on the load side of a GFCI device, and is why using these newer portable generators are not a very good way to try to back up a house panel, now if there was a separate service disconnect and the panel in the house was a sub panel then yes it would be possible if a 3-pole transfer switch was used.
jwelectric
Senior Member
- Location
- North Carolina
I have found that using a #12 cord from the receptacle on the generator to the load being served a very easy and cost effective way to use one of the small stand-alone generators.
I do have a hard time wrapping my mind around why anyone would want to connect one to a panel for.
I do have a hard time wrapping my mind around why anyone would want to connect one to a panel for.
generator faulting
Just like to say thanks to hurk27 for your input and other moderators. As luck would have it the service disconnect is outside the house
in a combo meter and disconnect switch [100 amp]. Load side feeds. the transfer switch, which in turn supplies sub panel. From your post it seems that replacing the existing 2 pole transfer switch with a 3pole transfer switch which isolates the neutral should solve the problem. Comments would be appreciate.
Just like to say thanks to hurk27 for your input and other moderators. As luck would have it the service disconnect is outside the house
in a combo meter and disconnect switch [100 amp]. Load side feeds. the transfer switch, which in turn supplies sub panel. From your post it seems that replacing the existing 2 pole transfer switch with a 3pole transfer switch which isolates the neutral should solve the problem. Comments would be appreciate.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Sorry, but it will fix the problem, there will not be a neutral/ground bond on the LOAD side of the transfer switch. You cannot use an interlock kit if that's what your thinking because it does not switch the neutral. It has to be a regular three pole(assuming this single phase) transfer switch. You never bond on the load side of the transfer switch.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Yes, that will solve your problem.
It don't sound like we're getting the complete story on this one.
If there was a "30 Amp Inlet" wired to a transfer switch, then why was'nt it wired correctly in the 1st Place?
Did he have an earlier year model Generator before that didnt have GFI Protection on it and then bought a new 8kw and now it doesnt work?
Sounds to me like he may have gotten a newer generator with GFI Protection and tried to plug it into the old inlet
or
If this is the Generator he had all along and someone wired a Transfer Switch and Inlet for it to run his house they wired it wrong to begin with.
JAP>
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
And you knew this from the OP? from the OP and the fact that the GFCI was tripping it seemed to me that there was a neutral to ground bond such as trying to transfer a main service panel which would have a main bonding jumper, and as such even a 3 pole transfer switch would not have fixed it, but in light of the new information that in fact he is serving a sub panel now I agree that a 3 pole transfer switch is what is needed, and making sure the house has no boot legged grounds such as using the neutral used as a ground in a 3-wire electric dryer or range feed, as these will have to be updated to 4-wire feeds, also that no grounding electrodes are ran to this sub panel as these will also trip the GFCI if bonded to the neutral.
Also I want to remind the OP that with only a 8kw generator it will be imperative that you fully instruct the home owner that with a manual transfer switch (which is the only thing allowed by the NEC because of the possibility of over loading the generator) that the owner will have to load shed (turn off any un necessary loads) this should be pre calculated and the breakers marked so the homeowner will easily know which breakers to turn off before ever transferring into the load, or damage to the generator can result, I have seen a few burn out the alternator after a few severe overloads, although it should trip the breaker on the generator many will not take this kind of abuse if it happens very often.
To test for any grounded neutrals to make sure the installation will work, turn off the main disconnect, remove the neutral from the disconnect to the panel at the panel end, then test with a ohm meter for any resistance between the neutral bar and the grounding bar in the sub panel, if any resistance is found then the fault must be tracked down and fixed, look for three wire range or dryer feeds, are one common thing to run into, also depending upon when this house was wired, this sub panel must be fed with 4 conductors from the disconnect (or a metal raceway that is allowed to be a EGC) these are some of what you could run into.
Also make sure to reconnect the neutral that was removed in the above test before turning back on the main disconnect as it can result in damaging equipment or cause a fire if not done and power is applied.
Last edited:
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Question: do these newer generators have the equipment grounding terminal bonded to the neutral?
If not why would the GFCI trip, unless there was a fault in the generator itself? All current going out will return through the GFCI until there is a fault on the generator side of the GFCI, only then is it possible to have unbalanced current through the GFCI.
The previous generators generally did not have a bond between the neutral and equipment grounding conductor and this had to happen in the premises wiring. The equipment ground of the generator did "float" unless it was connected to a premises wiring system.
If not why would the GFCI trip, unless there was a fault in the generator itself? All current going out will return through the GFCI until there is a fault on the generator side of the GFCI, only then is it possible to have unbalanced current through the GFCI.
The previous generators generally did not have a bond between the neutral and equipment grounding conductor and this had to happen in the premises wiring. The equipment ground of the generator did "float" unless it was connected to a premises wiring system.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
All portable generators will have a neutral to frame bond which is also used as an equipment ground, this is no different then the main bonding jumper in the service disconnect, as these bonds are ahead of any GFCI device the GFCI will not care about it, only after a GFCI device a neutral to ground bond will cause the GFCI to trip, also a GFCI does not need any current in a circuit to trip on a neutral to ground fault or bond, this is because there is a 120hz injection coil in the that will provide the source current that will allow the GFCI to trip as soon as there is a neutral to ground fault, AFCI's with ground fault protection (30ma) do not have this coil and will not trip until a load is applied to the affected circuit.
Also the lack of a neutral to frame bond will not affect the operation of a GFCI, as they will still function the same as when we install them on ungrounded circuits in a house, they can care less about a ground ahead of it only after it (load side).
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I fully understand what you said but disagree that all portable generators have a neutral to frame bond, and would even lean towards saying most do not - at least before they started putting GFCI on the twist lock receptacle, which is what I was asking about. I have not encountered one of those yet is why I ask.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
You are correct, we have had this discussion before on this, I personally own several like this. The first time I ran across the problem was with my Uncle's new Honda generator he bought years ago. It had a GFCI breaker built in, and would not set when plugged into his hunting cabin due the neutral/ground bond at the cabin.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Was this generator frame bonded to neutral within the generator? If not I don't see where the fault current will flow to trip the GFCI. The monitoring CT of that GFCI device will see no imbalance unless something returns outside the monitoring CT. If there is no frame to neutral bond that is impossible unless something is damaged in the generator and a path is developed, which as far as I can see that is all the GFCI is going to protect you from. Otherwise it should never trip unless there is a problem between the GFCI and the generator windings. The frame can possibly be same potential of any conductor of the system if there is a fault, but no fault current flows until there is a second fault somewhere, that is just the nature of an ungrounded system.
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