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

[daybreak1998]

Howdy,

Here is a cut and paste from another PTO generator manufacturer
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GENERATOR AC NEUTRAL CONNECTIONS

The generator is shipped from the factory with the neutral ungrounded. (Neutral floating, i.e.; no electrical connection between neutral and ground connection).

The required status of the neutral depends on how the PTO generator is to be used. The NEC (National Electrical Code) requires the following.

*Emergency Supply for a Fixed Wiring System -This is the case when the PTO is used to provide emergency backup power for a fixed wiring system. This requires the output of the generator to be connected to electrical load though a double-throw transfer switch. The neutral is NOT to be connected to the ground terminal. This is how the PTO generator is supplied from the factory, no changes are required.

*Separately Derived Source --This is the case when the PTO generator is to supply only loads connected by cords plugged into the outlets or fuel capacity connector. This is the case when the load is not normally supplied by the Utility source or is not part of a fixed wiring system.

The neutral is to be connected to the ground terminal in the control panel.

1. Remove the control panel cover.
2. Locate the #4 AWG wire loop on the ground terminal.
3. Disconnect one end of the wire loop and attach it to the neutral connection terminal.
4. Tighten the retaining nuts on both terminals.
5. Replace the control panel cover and secure the fasteners.

GROUNDING THE GENERATOR

The National Electrical Code requires that the frame and external electrically conductive parts of this generator be properly connected to an approved earth ground. Local electrical codes may also require proper grounding of the unit. For that purpose, a GROUNDING LUG (Figure 13) is provided on the unit. Generally, connecting a No. 6 AWG (American Wire Gauge) stranded copper wire to the grounding lug and to an earth driven copper or brass grounding rod (electrode) provides adequate protection against electrical shock. However, local codes may vary widely. Consult with a local electrician for grounding requirements in your area.

DANGER Do not connect the grounding wire to any pipe that carries flammable or explosive substances fire or an explosion may result.

Proper grounding of the generator will help prevent electrical shock in the event of a ground fault condition in the generator or in connected electrical devices. Proper grounding also helps dissipate static electricity, which often builds up in ungrounded devices.
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The emergency supply for a fixed wiring system is where you want to be. Unless you are hard wiring it in your system. What type of outlet does the PTO generator have?

I use the modular anderson connectors with mine, with all 4 wires in place. Known as a full power plug.

 

[stonypass]

What type of outlet does the PTO generator have?

The generator has the following outlets: (1) 20A 120V 5-20R / (1) 30A 240V L14-30R Twist Lock / (1) 50A 5-50R Straight, and here is the Generator
Appears to be identical to this one as well and there is a manual for it on that site, but it's been of little help and the companies support hasn't been either.
I'll be using the NEMA 14-50R outlet which provides 50a at 240v with a 4 wire 6ga cord, the output of the cord is a 50a twist lock female plug and the inlet box on the house is a male 50a receptacle.
My generator cord and the run from the inlet box to the breaker will be under 30ft total.

I've installed a 50a double pole breaker in the upper right hand corner of my breaker box, and will be using it with an interlock kit to make sure the main and generator breakers can't be on at the same time.
The electric meter and a ground rod that my breaker box is connected to are within 30ft of where the generator would be operated.
Your thread here is what got me going on the interlock in the breaker panel.

If your attaching yours with an interlock, then your setup is like mine except for the higher current connectors.
How are you running yours, did your leave Neutral and Ground floating, do you attach the generator to a ground rod?

 

[daybreak1998]

If your attaching yours with an interlock, then your setup is like mine except for the higher current connectors.
How are you running yours, did your leave Neutral and Ground floating, do you attach the generator to a ground rod?

Howdy,
I actually am using three different methods. The systems all have the generators using floating neutral. All of my generators methods of connection are all portable. I am tying into a fixed wired system. From my thread here you can see I use a meter panel with interlock, a generac exl6500 attached, then a generlink system with a ETQ 7250 attached with provided cordset. I then have the Tiger Power 30kw, which is connected via the anderson 350amp connectors and 2/0 wire to the transconnect TC-200M26W. This special connection was installed by my utility, and verified all was proper with floating neutral, and all 4 wires connected and grounded. If you look back at my generator-transfer-switch-connection-choices thread, you can see each of the panels. You can click on the pictures and zoom in for better views.

With all the comments here, I would say you are emergency use, fixed wiring system, and the ground is the panel, and you use all 4 wires from generator to interlock breaker. Just verify you do indeed have floating neutral configured.

 

[aczlan]

This is very important because the generator in question has been designed, manufactured, and tested against certain safety standards. The generator can't just be rewired and assumed safe. It's not. It was not intended to operate that way and there may be associated hazards. One obvious hazard is electrocution, as with no system bonding jumper in place, the equipment ground (generator chassis) can become energized. The possible ways this can happen is limited only by one's imagination. Another hazard is that the fault current path is changed. The new connections/configuration should be tested to see if it will carry the fault current that the generator can supply. That and many other tests were conducted before the generator was available as a commercial product.

Many generators DO have as part of their instructions how to bond/unbond the neutral depending on how they are connected and they ARE tested that way.

The correct way to do the installation is to use a three pole transfer switch, if the generator will allow for a solid connection. If it doesn't allow for a solid connection, then there really is no safe way to connect this generator to the premises wiring system. The OP asked what is "for best safety". That's why I'm answering. There are many possible ways to connect the OP's generator to his premises wiring system, but for best safety, follow the NEC.

Have you looked at a small (30ish amp) "emergency transfer switch" recently? How about a "Generlink" (which is usually sold by a utility)? How about a Genrac ATS?

All use a 4 prong plug or 4 solidly connected wires with an unbonded neutral at the generator. In fact (from the generlink site):

NOTE: Per the National Electric Code, all generators must have a "floating neutral " when used with the GenerLink Automatic Transfer Switch. Please refer to the generator operation manual for bonded neutral specifications.

Here is a Generac ATS picture as installed by "Robert Welborne - Master Electrician & State Electrical Inspector": http://www.rrelectriccompany.com/files/100_0654.JPG Note that the neutral is NOT switched and as such the generator has a unbonded neutral and a 4 wire connection to the ATS.

The short of it is:
IF you are using a 3 pole (hot, hot, neutral) transfer switch to disconnect things between the meter and the panel - Bond neutral to ground at the generator and use a 3 wire cord.
IF using a 2 pole transfer switch such as a generlink, an interlock, a/b switch panel, etc - Do NOT bond neutral to ground at the generator and use a 4 wire cord.

Aaron Z

 

[stonypass]

With all the comments here, I would say you are emergency use, fixed wiring system, and the ground is the panel, and you use all 4 wires from generator to interlock breaker. Just verify you do indeed have floating neutral configured.

There is a ground lug on the receptacle panel of my PTO generator, should I run an additional wire from it to the ground rod at my service entrance?
Seems redundant to me, as one of the four wires in my generator cord is also attached to ground on the generator panel and connects to the bonded Neutral/Ground in the breaker panel then runs to the ground rod.

Are you running a separate ground wire on yours?

 

[aczlan]

There is a ground lug on the receptacle panel of my PTO generator, should I run an additional wire from it to the ground rod at my service entrance?
Seems redundant to me, as one of the four wires in my generator cord is also attached to ground on the generator panel and connects to the bonded Neutral/Ground in the breaker panel then runs to the ground rod.
Are you running a separate ground wire on yours?

If close enough to the existing ground rods, I would use them. If not, I would drive a new one. Either way, I would ground the frame of the generator using the lug you mentioned.

Aaron Z

 

[Hillman314]

(Ignoring the issues that come with using a cord/plug instead of hardwired)

Ok, you are using a 4-wire connection between the panel & generator: (2 hots, 1 Neutral, 1 ground). This is good. You do NOT have a seperately derived system when the neutral is unswitched when you wire the neutral of the generator to the neutral of the panel. It is only at the panel where the neutral should be bonded to ground (rod).

The ground wire (green) in your cord should also connect the chasis of the generator to the ground bus in your panel (which is in turn connected to an existing ground rod). Think of this as the protection against the generator's frame developing a dangerous touch voltage. (Actually, it insures that a fault current to the frame will have a low resistant path to ground and therefore develop a fault current large enough to trip a fuse/breaker.) A ground rod at the generator is not required (but wouldn't hurt as long as the nuetral and ground are seperated at the gen.)

The term "floating neutral" is a misnomer, it will be connected to your panel's neutral through the cord, and thus pegged to ~0 volts (ground) by the neutral connection to ground at your panel. This insures that the 240V from the gen is divided into 2-120V circuits (and not 80V and 140 volts, for example, if the neutral was unconnected to anything (i.e. truely "floating")). (One can see that if the neutral was switched we would then need a connection of the generator's neutral to ground (rod) at the gen.)

What's important is: The neutral (white) and the chasis ground (green) should not be connected together, by any means, at the generator. System-wide, they should only be connected at one place (in your existing panel). Otherwise, you would have normal neutral current also running on the parallel chasis ground conductor (green). As per Ohm's Law, a current through this conductor (with some resistance) will cause a voltage to develop across that resistance, and the generator's chasis connected to this ground conductor with neutral current running through it would see that voltage above ground (O volts); that could be shocking if you then touch it.

(Caution if you ever use this generator (with it's non-fixed, quick detachable cords/plugs) to power something else, where the neutral & ground aren't bonded as they are in your panel, (and you have a seperately derived system), you may not trip off on a ground fault.)

 

[Qapla]

OK ... not to confuse the discussion, but I have an additional question.

It has been stated that the Ground and Neutral should be un-bonded at the Generator but that they are bonded in the panel box.

Well, on my home we have a panel at the power pole where the neutral and ground are bonded. Then, due to distance from the pole to the house, we were required to have a panel just outside the house. This panel has un-bonded neutral. Then, there is the panel in the house that also has the neutral nu-bonded.

If I connect a generator to the panel outside the house, not the one that is further away at the pole, should the neutral of the generator be bonded or not since the neutral in the panel is un-bonded?

 

[DarkBlack]

I hang my head and try to say this again for all to listen or ignore (Jpc gets it ) If you disconect the neutral to ground jumper on the jenny.... You loose the ground conductor from the genny to the house during a fault. It think it must be one of those abstract principles that somehow boggles smart minds. Draw it on paper.... The portable genny has a 240v secondary, with a center tap. Those three outputs only want to flow to each other- not to derived gnd. If a 120v whatever, in your house shorts to gnd, it's only motive force is back to the center tap of your genny if you remove the bond. This renders the ground conductor of your patch cable dead weight, it's only motive is back on the neutral conductor.

 

[Hillman314]

I hang my head and try to say this again for all to listen or ignore (Jpc gets it ) If you disconect the neutral to ground jumper on the jenny.... You loose the ground conductor from the genny to the house during a fault. QUOTE]

I don't think that is so, the neutral (aka "grounded conductor) and the (equipment) grounding conductor are bonded at the house panel, the fault current will re-enter the neutral back to the jenny's winding here.

 

[Hillman314]

Qapla: If you're not switching the neutral as part of the transfer from utility to generator power, then don't jumper the neutral and ground at the generator. The neutral and ground should only be bonded in one location. (You really have three panels????)

 

[JPCjr]

I appreciate your thoughts, but I'm wondering how many portable generators used for temporary emergency power are installed with a solid connection?

People violate the code all the time, but that doesn't mean it's safe to do so.

 

[JPCjr]

Many generators DO have as part of their instructions how to bond/unbond the neutral depending on how they are connected and they ARE tested that way.

Yes, I realize that. I mentioned that in one of my first posts in this thread, but it doesn't apply to the generator being discussed here. Look at the photos the OP posted. There isn't a system bonding jumper that can be removed. Also, the manual in the link he posted has no instructions for removing the bond between equipment ground and neutral. It's permanently configured as a separately derived system and shouldn't be changed. A three pole transfer switch should be used, but the OP does't want to do that. So he's left with a dilemma.

 

[daybreak1998]

There is a ground lug on the receptacle panel of my PTO generator, should I run an additional wire from it to the ground rod at my service entrance?
Seems redundant to me, as one of the four wires in my generator cord is also attached to ground on the generator panel and connects to the bonded Neutral/Ground in the breaker panel then runs to the ground rod.

Are you running a separate ground wire on yours?

Howdy,

No, I am not using any seperate ground rod. The 2/0 welding cable is 10 feet, and is my ground. This is attached to my central farm distribution. Meter with lugs which then feeds 5 other buildings.

The same thing with the generlink unit, and the interlock. All generators are portable and are only brought out and attached when needed.

I guess some people here might have a tool in their hand, and then attach a awg #6 wire to a ground rod as to not think there plug ground is adequate.

 

[Victory Pete]

As a licensed electrician this topic does get my head spinning. There are many different situations to consider. It is best to call in the local inspector for advice although sometimes they interpret the code differently. The last generator install we did we ran 1 1/2" emt as ground and neutral and 2 phase conductors. I am assuming the generator itself had unbonded neutral and ground. There was no neutral disconect in the automatic transfer switch. We installed a ground rod at the generator.

VP

 

[stonypass]

If a 120v whatever, in your house shorts to gnd

Wouldn't this just trip its own breaker in the box?

 

[Hillman314]

Wouldn't this just trip its own breaker in the box? : Only if the fault current is big enough to trip the breaker. To put it another way: Only if there is a path of low (enough) resistance back to the center tap (neutral) connection of a transformers or generator's winding, thus the circuit's loop is completed and current will be high enough that the breaker will trip. The "best fault" situation is when the fault is to something that has a grounding (green) conductor attached to it, then there's a low resistance path back to the neutral of the generator (because the grounding system and neutral are bonded in your house panel).
If there's a fault to something not "grounded" well enough that the breaker doesn't trip, then that object will become energized, and a person who touches it may become the path of least resistance.

Without a grounding (green) conductor to take the fault current back to the winding (in a "short" circuit), one is relying on earth as part of the circuit's loop back to the winding. (a "long circuit" ? that is, the path would be from that shorted object in contact with the ground, throught the ground, into the ground rod, to the neutral bonded to the ground in your panel, back to the generator's winding neutral tap. Here, the ground (earth) is not a good conductor, and the fault current in this scenario may not be enough to trip the breaker.

A couple things about grounding that most people don't realize: 1. The biggest function of a ground rod on a electrical service is to provide a 0 volt reference (period). A gound rod's function is not "to send fault current into the ground" (except for lightning strikes I suppose, but I digress) 2. The point of grounding (green) conductors connected to equipment is not to send fault current to the ground rod/earth, it is to have a low resistance path (i.e. a "short" circuit) to the neutral winding of the power source (transformer or generator) during a fault. Low resistance = high current = tripping breaker/fuse. That is why the neutral and grounding conductor is bonded in the panel. 3. The reason they are bonded in only one place so that normal neutral current does not have a parallel path on the green grounding conductor, otherwise normal neutral current (times any resistance) would = a voltage (Ohm's Law) on the various normally non-current carrying metal parts that are connected to the (green wired) grounding system.

 

[Hillman314]

^ Sorry, bit of a long-winded ramble. I'll work on keeping them short.

 

[SPYDERLK]

I hang my head and try to say this again for all to listen or ignore (Jpc gets it ) If you disconect the neutral to ground jumper on the jenny.... You loose the ground conductor from the genny to the house during a fault. QUOTE]

I don't think that is so, the neutral (aka "grounded conductor) and the (equipment) grounding conductor are bonded at the house panel, the fault current will re-enter the neutral back to the jenny's winding here.

Yes. A longer path, so some potential will develop on gen chassis -- but no alarming amt unless there is a connection or conductor fault.
...As to this stuf about low resistance paths: short and/or large wires are extremely low resistance. Small Fractions of an ohm. In any functioning setup where all 4 conductors make their respective contacts there is always a low enuf resistance current path to blow breakers and keep case potentials safely low in a fault. It is the contacts that are of paramount importance and that should be monitored if they are not bolted. Since a resistance at a contact is concentrated at a single point any significant amount will heat it enuf to cause a degrading chain reaction. That is why plug connections are frowned on. You cant trust people to be aware. However, if you are you clean, and then spot check the plug under significant 120/240 loads and assure that relative temp is 0 or very small in relation to that of the wire. And you further know that this only proves 3 out of 4. The ground contact is not proven since it is not carrying current. Best to bring a pigtail out and bolt it.
larry

 

[DarkBlack]

Wouldn't this just trip its own breaker in the box?

It might not with limited ampacity of a jenny. Also picture this: a pinhole in the enamel of your drill press's motor's stator finally conducts to the housing. It happens to have shorted 1/2 through the length of the winding. Now you have current limited potential on your ground system. The genny won't flow enough current at this resistance to trip your house breaker. Since you disconected the gnd bond at the generator, The only path to flow current to reduce this volatge is through the neutral wire of your genny cord. Now what if the plug connection of the neutral is less than great? This is a case where you would have been better to leave the gnd-neutral bonded at the genny.