Grounding a portable generator

I believe that Part III of Article 551 applies to generators that are mounted in or upon the RV; not separate units that may be on the ground away from the RV and connected to it by a cable. That conclusion comes from the terms and definitions used in Part III of Article 551.

Therefore, the code doesn't apply to the generator described in the original post. It would apply to the CABLE used to connect that generator to the RV, and the practices used to safely connect to that generator may be appropriate when such a generator is used.

Consequently, there is no requirement that a generator not mounted in or upon the RV be listed for use in an RV.

Where I quote the code and make comments, my comments are in italic.

551.1 Scope. The provisions of this article cover the electrical conductors and equipment other than low-voltage and automotive vehicle circuits or extensions thereof, installed within or on recreational vehicles, the conductors that connect recreational vehicles to a supply of electricity, and the installation of equipment and devices related to electrical installations within a recreational vehicle park. (A generator owned by an owner of a recreational vehicle, and set upon the ground some distance from the recreational vehicle, which may or may not be in a recreational vehicle park, is not an "electrical installation" and does not fall within any of the terms of the SCOPE of Article 551.)

551.30 Generator Installations (Note the term installations.)

(A) Mounting. Generators shall be mounted in such a way as to be effectively bonded to the recreational vehicle chassis. (Mounting implies in or upon; mounting doesn't mean sitting on the ground 50 ft away.)

(C) Installation of . . . . Storage batteries and internal-combustion-driven generators shall be secured in place . . . ("Secured in place" excludes generators not in or upon the RV.

jwelectric said:

I would recommend that you have this done by a professional. It needs to be done internal of the generator such as this illustration shows.
[pic here]
Here the bond was removed because the “bonding†took place at the main for the building. The “bonding†can not occur at both the generator and the building.

NO! NO! NO! this is not the way to “bond†the generator and is doing nothing but causing a more dangerous situation.

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Who would I get to check/change it for me so it can be done correctly? An electrician?

jwelectric said:

In my area there is a slew of RV parks and I get calls all the time about someone using a generator that is not bonded and feeling a tingle on rainy days until I ask on the phone about the electrical connection before I go out on the call. 99% of these calls are about the remote generator that is not properly listed for the use and are not bonded.

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Operating a generator that is exposed to rain sounds like a bad idea without even thinking about it.

I'm getting way off topic here but for some reason, our cable TV wires in the house here give off a mild shock on the outer part usually. The cable guy blamed the house's grounding. Sounds more like a grounding problem with the cable company's wires to me. I was having a problem with the internet constantly so a guy came out and was checking the connections and he got the shock twice. It is like, as you put it, a tingle. He blamed the ground problem with the house for the internet disconnecting constantly which was nonsense. It has worked fine before and since the constant disconnections for a couple years and the cable line still gives off a shock when you are trying to screw/unscrew connections. It doesn't do it as soon as you touch it. Its like you have to keep hold of it a while before the current builds up and gets back to you. He also tried to blame the wet ground outside yet the shocks happen in completely dry weather as well.

The part I like best is when it is still raining and the generator has been set inside a cavity of the RV to protect it from the weather. Now it just became a mounted generator and I recommend to the park manager to either have the RV owner sign a wavier of liability or evict then from the park.

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Yeah, bad idea. Even if I wanted to do that (which I don't) my trailer only has one external compartment and the generator can't even fit into it so I can't possibly do it.

The NEC does not require that the generator being used on a RV be listed because the NEC is making a lot of money from the sale of listed generators but instead the NEC requires that generators be listed for the purpose as a safety issue.
The danger comes when the RV owner wants to save a little money and buy something just because it works without understanding the danger involved.

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The NEC require proper RV-rated generators to ONLY be used vehicle-mounted compartments. It does not appear to say that you cannot use a portable generator for an RV anywhere in the NEC code as Bob pointed out:

Bob NH said:

I believe that Part III of Article 551 applies to generators that are mounted in or upon the RV; not separate units that may be on the ground away from the RV and connected to it by a cable. That conclusion comes from the terms and definitions used in Part III of Article 551.
................
Consequently, there is no requirement that a generator not mounted in or upon the RV be listed for use in an RV.
................
(A) Mounting. Generators shall be mounted in such a way as to be effectively bonded to the recreational vehicle chassis. (Mounting implies in or upon; mounting doesn't mean sitting on the ground 50 ft away.)

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This is exactly what I get from reading this section of the code.

I thought I'd post a follow-up to this thread.

I picked up the generator out of layaway today. The exact make/model of it is a Coleman Powermate Vantage PM0473505. Quite a nice generator. It seems to lack GFCI however but does have breakers with "reset" buttons. I can solve the GFCI issue with a plug-in GFCI adapter for about $10 for the 15A outlets which I will be using only. It also has twistlocks in the form of 120V/30A as well as a 240V/20A. In addition it has 12V/15A out via a special plug-in cable with clamps at the end for battery (charging I suppose?).

I put some gas in it, checked the oil (full but should probably be replaced) and the air filter (not bad at all) and then attempted cranked it up. After fighting with it then realizing I had the kill switch on, I finally got it going and it worked fine.

Coleman lacks the manual on the website so I have emailed them requesting it.

There is a label on it saying that the neutral is floating so it's in fact not bonded to the frame. I took it to an electrician who is one of my brother's in-laws and he said that bonding neutral to ground won't do much of any good.

Near as we could figure due to the construction of the generator making it impossible easily access the electrical outlets to verify, the neutral is floating as the label on the generator says but the ground of the generator outlets is NOT bonded to the frame. There are rubber separators under the engine to isolate the engine from the frame and the engine has a "ground" (not "grounding") terminal for hooking up a rod.

So is it safe to leave the neutral floating as the generator was made and just bond that ground terminal on the engine to the frame of the generator like he said I could do?

Or do I need to take it to a generator repair shop and have them bond the neutral to ground and then bond the neutral/ground to the frame? They will have to remove the engine to even access the panel where the outlets are due to the construction of the unit.

I suggested to the electrician about using a plug-in GFCI adapter for extra safety and he said those are the most problematic piece of equipment there is and I guess basically said it won't do much to add safety and that it may just end up tripping all the time.

He said if I'm so concerned about safety I should just use a ground rod which I don't want to have to do since it's a portable, temporary use generator that is going to be moved from place to place all the time. But he more or less said it was fine to use any is.

Any opinions that say otherwise..?

Please tell me this is not one of those crazy units with no 120/240v twistlock.

Speedy Petey said:

Please tell me this is not one of those crazy units with no 120/240v twistlock.

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No, it's not.

It has 120V/30A and 240V/20A twistlocks in addition to a standard 120v/15A duplex and a special 12V/15A outlet for a cable with clamps. I don't have a photo at the moment but trust me it does have twistlock for the higher amerage/voltage above 120V/15A.

From this description it seems there is no 4-wire 120/240v twistlock receptacle. Like an L14-20R receptacle.
If so there is NO way you can connect this genset to your house's system.

Speedy Petey said:

From this description it seems there is no 4-wire 120/240v twistlock receptacle. Like an L14-20R receptacle.
If so there is NO way you can connect this genset to your house's system.

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I have no intentions of wiring up to a house. It is going to be used for a 1967 Shasta travel trailer with a standard 3 prong 15A electrical hookup. A standard 120V/15A outdoor extension cord is what is used to plug it in to power and therefore that is what I will be plugging into on the generator.

You may be correct about it not being twistlock but since it's not going be used for anything beyond my travel trailer/camping it shouldn't matter.

Cubey said:

There is a label on it saying that the neutral is floating so it's in fact not bonded to the frame. I took it to an electrician who is one of my brother's in-laws and he said that bonding neutral to ground won't do much of any good.

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If the grounding terminals of the receptacles are bonded to the frame and the neutral point of the generator is not then there is nothing to open the overcurrent device in the event of a ground fault.

Cubey said:

There are rubber separators under the engine to isolate the engine from the frame and the engine has a "ground" (not "grounding") terminal for hooking up a rod.

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This lug if to bond the engine to the frame not to a rod although you could drive a rod if you so chose. 250.34 of the NEC says as long as the generator is not connected to anything then no rod is needed.

Cubey said:

So is it safe to leave the neutral floating as the generator was made and just bond that ground terminal on the engine to the frame of the generator like he said I could do?

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No it is not safe and is a death in the waiting.
250.34(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be bonded to the generator frame where the generator is a component of a separately derived system.
250.26 Conductor to Be Grounded — Alternating-Current Systems.
For ac premises wiring systems, the conductor to be grounded shall be as specified in the following:
(1) Single-phase, 2-wire — one conductor
(2) Single-phase, 3-wire — the neutral conductor

Cubey said:

Or do I need to take it to a generator repair shop and have them bond the neutral to ground and then bond the neutral/ground to the frame? They will have to remove the engine to even access the panel where the outlets are due to the construction of the unit.

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Yes take it to someone that has knowledge of generators and have the bonding jumper installed.

Cubey said:

I suggested to the electrician about using a plug-in GFCI adapter for extra safety and he said those are the most problematic piece of equipment there is and I guess basically said it won't do much to add safety and that it may just end up tripping all the time.

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When is it possible to have to much safety?

Cubey said:

Any opinions that say otherwise..?

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As outlined above.

jwelectric said:

If the grounding terminals of the receptacles are bonded to the frame and the neutral point of the generator is not then there is nothing to open the overcurrent device in the event of a ground fault.

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I thought I understood everything but now I'm confused again. As I understood it the generator's neutral and ground had to be bonded at the generator.

Yet now I've been told otherwise by the electrician I know. He seems like he may not fully know what he's talking about since he first told me that I could bond neutral to ground at the trailer's panel and then went back on that a bit later and said it needed to be isolated. And then also said I don't really need any bonding at all and that the breaker(s) would kick off if I left the generator's neutral floating. Then said not to bother with GFCI which doesn't make a lot of sense to me. Sounds like I'm getting bad advice every which way I turn in one way or another.

Someone else told me to run the generator while plugged into the trailer, take a voltage meter and touch one to the trailer chassis and the other to the ground terminal on the generator and see if the reading is over 28v and if it is, it's dangerous. Anyone ever heard of doing that?

I read an old '98 usenet post pointing out that if the trailer is not "grounded" (has rubber tires isolating it from earth) and nor is the generator (on plastic wheels) then there is no path to earth and that if somehow the chassis of the trailer became energized (through ground which is actually isolated from neutral/hot so it can't even!), it wouldn't hurt you.

While I'm not sure that makes sense, the following actually DOES make sense (unless I'm greatly mistaken).

If neutral is floating on the generator and the trailer (neutral not bonded to ground/chassis at all) and there was some sort of problem, the neutral would be isolated from the chassis/"ground" of the trailer and generator with no path to earth due to rubber tires. So stepping on wet ground even in bare feet wouldn't kill you since the generator is up on plastic/rubber wheels isolating it from earth just like the trailer.

For example, the trailer and generator can be sitting in a shallow puddle of water with me also standing in it bare footed but it shouldn't do anything at all to me since the juice isn't being poured into the water or earth... unless of course the frame of the generator is bonded and I were to touch it so maybe bonding to the frame isn't such a good idea.

It would be contained to the hot/neutral and should trip the breaker without endangering anyone. But if I were to bond neutral to ground, the chassis of the trailer would become a risk under certain conditions.

It currently has crappy hard plastic craftsman wheels on but I plan to upgrade them to larger, pneumatic tires with tubes inside for easier moving and also better isolation from earth.

Cubey said:

I thought I understood everything but now I'm confused again. As I understood it the generator's neutral and ground had to be bonded at the generator.

Yet now I've been told otherwise by the electrician I know. He seems like he may not fully know what he's talking about since he first told me that I could bond neutral to ground at the trailer's panel and then went back on that a bit later and said it needed to be isolated. And then also said I don't really need any bonding at all and that the breaker(s) would kick off if I left the generator's neutral floating. Then said not to bother with GFCI which doesn't make a lot of sense to me. Sounds like I'm getting bad advice every which way I turn in one way or another.

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It depends on how you intend to use the generator. If you are going to plug a cord into the generator and then plug an appliance into the cord, there is no physical connection between the appliance and the RV, then there is no need to install a grounding electrode as outlined in 250.34.
If you intend to connect the generator to the panel of the RV then 551.30 applies and there are special bonding requirements to ensure that the premises wiring of the RV is bonded to the frame of the generator.
Yes you are getting a lot of “bad†advice.

Cubey said:

Someone else told me to run the generator while plugged into the trailer, take a voltage meter and touch one to the trailer chassis and the other to the ground terminal on the generator and see if the reading is over 28v and if it is, it's dangerous. Anyone ever heard of doing that?

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I read something about this is a book titled “What Not To Doâ€
How silly can any one person get to be in one life time?

Cubey said:

I read an old '98 usenet post pointing out that if the trailer is not "grounded" (has rubber tires isolating it from earth) and nor is the generator (on plastic wheels) then there is no path to earth and that if somehow the chassis of the trailer became energized (through ground which is actually isolated from neutral/hot so it can't even!), it wouldn't hurt you.

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Please don’t try to prove that this is correct as I will leave you with a very sad family.

Cubey said:

While I'm not sure that makes sense, the following actually DOES make sense (unless I'm greatly mistaken).

If neutral is floating on the generator and the trailer (neutral not bonded to ground/chassis at all) and there was some sort of problem, the neutral would be isolated from the chassis/"ground" of the trailer and generator with no path to earth due to rubber tires. So stepping on wet ground even in bare feet wouldn't kill you since the generator is up on plastic/rubber wheels isolating it from earth just like the trailer.

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Do you understand the term “difference in potential†or touch differences? If the neutral point is floating in the generator then there is no effective ground fault path in the generator itself. In the event of a fault to metal be it the frame of either the generator or the RV there is nothing to clear the fault.
This is especially important if the generator is connected to the wiring system of the RV. If the generator is connected to the wiring system of the RV be it intentional or not then the entire RV is at the same potential as the output of the generator.
In this case you would not need to be standing in a puddle of water or even on the ground, you could be standing in the middle of the floor to the RV and become part of the current flow or even dead.

Cubey said:

For example, the trailer and generator can be sitting in a shallow puddle of water with me also standing in it bare footed but it shouldn't do anything at all to me since the juice isn't being poured into the water or earth... unless of course the frame of the generator is bonded and I were to touch it so maybe bonding to the frame isn't such a good idea.

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Good idea or bad idea it is required to be bonded to the frame of a stand alone generator. I would think that those who are responsible for writing these codes would know a little more than someone who is constantly changing their mind about how to make the installation as you have pointed out above.

Cubey said:

It would be contained to the hot/neutral and should trip the breaker without endangering anyone. But if I were to bond neutral to ground, the chassis of the trailer would become a risk under certain conditions.

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In order for the breaker to trip the fault current must get back to the source. This is accomplished through the bonding of the frame of the generator to the neutral point. Without this bond there is no way for the fault current to return to it’s source and the overcurrent device WILL NOT OPERATE!!

Cubey said:

It currently has crappy hard plastic craftsman wheels on but I plan to upgrade them to larger, pneumatic tires with tubes inside for easier moving and also better isolation from earth.

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I beseech you to seek the help from a professional before someone is hurt or even killed with this setup.

Apparently, no one in this town knows anything about working on generators other than the engines. I've been playing phone tag for the last 20 minutes. I called a contractor sales/rental place since they deal with selling/renting generator, they told me to all an armature place that only deals with alternators, they told me to call some other place that only deals with very old alternators/generators in autos, tractors and the like and has no idea who would work on it.
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Edit:

Found one place but they deal with large home generators. I am getting VERY pissed off at this point. No one can give me a straight answer locally. I'm about ready to just try to do it myself!

jwelectric, take a look at the following:

All Champion Power Equipment generators, with the exception of our 40012 and all CSA-certified generators sold in Canada, have a "floating neutral", meaning that the neutral circuit is not connected to the frame or to earth ground. This also means that both legs on the receptacle are hot legs, which is normal for floating neutral generators. As a result, there is no specific hot leg and neutral leg wiring arrangement for the generator winding connection to the receptacle. The floating neutral configuration is common for applications such as connection to a recreational vehicle and connection to home power where the transfer switch does not switch out the neutral to ground connection.

The floating neutral eliminates the potential of being shocked by contacting a hot leg and the generator frame at the same time, which could occur if an electrical device such as a hand held tool suffered from an internal short circuit.

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According to that, a portable generator should have floating neutral for safety.

Do you understand my frustration and confusion? Some sources say to bond it and others say not to.

Generators. If the grounded (neutral) conductor in a transfer switch is not opened, the grounded (neutral) from the generator will be solidly connected to the utility’s service grounded (neutral) conductor. Under this condition, the generator isn’t a separately derived system, and a neutral-to-case bond must not be made at the generator or at the generator disconnect [250.20(D) FPN 1].

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What does it mean by "If the grounded (neutral) conductor in a transfer switch is not opened"?

If I am understanding it correctly, the so-called "transfer switch" (the plug on the RV) does NOT "open" the neutral conductor. It is always closed. When I have it plugged it, it is always linked to the generator until I unplug it. It's not on an actual transfer switch such as in a house where the grid electric is also wired up. Either the trailer is plugged into the generator OR it's plugged into grid power. It's never plugged into both at the same time and therefore doesn't use a transfer switch. *I* am the transfer switch basically.

I am awaiting a callback from an RV repair shop that I was told does a lot of generator repair work. A portable generator on wheels is basically the same as an installed/mounted RV generator since neither one has a ground rod and both are up on tires off the ground.

What a complete jerk the RV guy was! He said "Well, if you're confused, go to the library and get a book and will explain it. Have a nice day." and hung up on me. I was being completely nice and patient with the guy! All I got out of him before he hung up on me was that I could use it as-is but I might get a little shock. He was no help at all!!

Now you know the kind of people I am dealing with around here!

It's time to get back to "first principles".

A generator generates voltage between the two ends of the winding in the generator. If neither end of that winding is connected to "earth", then there is no potential relative to "earth". You could grab either wire (but only one) and would not be "shocked" (but I suggest that you test this with a meter that has a little load, not with your body).

If such an ungrounded winding became shorted to the metal part of the generator (a "ground fault") there would still be no potential (voltage) relative to earth. You could touch the generator structure while standing on the ground and not receive a shock.

Furthermore, that "ground fault" to the structure would not trip the breaker on the generator.
. . . NOTE: There are industrial systems that are intentionally ungrounded so that they will continue to run in the event of a ground fault. They are usually equipped with ground fault indicators so that ground faults can be detected and fixed.

Now let's assume that one end of that winding (We'll call it terminal B, and we'll call it "neutral") is connected to the metal structure and all of the non-electrical metal parts of the of the generator. If that metal structure is isolated from "earth" you still would not get a shock from touching either of the conductors while standing on the ground.

But if the other end of the winding (Terminal A) became "ground faulted" to the structure through a conductor that has passed through the breaker it would trip the breaker on the generator because the current would return to the other end of the winding through the metal parts of the generator.

Next, let's assume that the structure of that generator is connected to "earth", either through an intended conductor and ground rod or "accidently" through some minor conductor.

NOW, if you get a ground fault (terminal A connected to the structure) there would be a voltage relative to "earth" and whether or not it would trip the breaker would depend on whether or not the fault passed through the breaker or whether the ground was low enough resistance to trip the breaker.

So to be safe, IF you are going to ground the generator, then the neutral (one end of the winding) should be connected to the frame of the generator so that a fault from the other end of the winding to the frame will trip the breaker.

Now if you run a ground wire from the generator structure to the trailer structure, and DO NOT connect the neutral to the trailer structure, then if there is a "ground fault" of the hot conductor to the trailer or generator structure the current will return to the generator winding via the ground wire and should trip the breaker. Therefore, the structure of either unit should never be significantly above "earth" potential. This should apply whether or not there is a ground rod because the fault current will pass through the breaker and does not in any way depend on conduction through "earth".

If there is a GFCI anywhere in the circuit it will trip on any ground fault that occurs after the GFCI.

SOLUTION:
1. Connect a ground wire between the structures of the generator and the trailer.
2. Connect the "neutral" to the structure and ground wire at one end only. This provides the path for the fault current and doesn't put "neutral" current on the ground wire.
NOTE: My house generator neutral is not connected to the generator frame because it is connected to the grounding electrode (ground rods and water pipe) at the main panel neutral bar, and the ground from the generator is connected to the ground/neutral bar at the main panel.
3. You can provide some kind of connection to earth if you choose, but it is not necessary for the system to work or be safe. I would probably throw a chain on the ground to leak off any small capacitively coupled voltages that might give a little tickle if you stepped off the trailer into wet grass with with your bare feet while one foot was still on a metal step.

Bob NH said:

It's time to get back to "first principles".
If there is a GFCI anywhere in the circuit it will trip on any ground fault that occurs after the GFCI.

SOLUTION:
1. Connect a ground wire between the structures of the generator and the trailer.
2. Connect the "neutral" to the structure and ground wire at one end only. This provides the path for the fault current and doesn't put "neutral" current on the ground wire.
NOTE: My house generator neutral is not connected to the generator frame because it is connected to the grounding electrode (ground rods and water pipe) at the main panel neutral bar, and the ground from the generator is connected to the ground/neutral bar at the main panel.
3. You can provide some kind of connection to earth if you choose, but it is not necessary for the system to work or be safe. I would probably throw a chain on the ground to leak off any small capacitively coupled voltages that might give a little tickle if you stepped off the trailer into wet grass with with your bare feet while one foot was still on a metal step.

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Okay. If I understand you correctly, you are saying I should do all 3 things above...

1: The chassis of the trailer is connected to the "ground" wire of the trailer's receptacle and the external hookup for power. So the ground wire in the trailer is connected to the chassis and leads back to the generator's ground via the extension cord. So it's already linked as you said it should be above if I'm understanding you.

2: I need to bond either the trailer's panel or the generator's panel. Technically the trailer's panel is NOT supposed to be bonded since it's a sub panel but it wouldn't exactly be unsafe to do so since it would provide "proper" bonding inside an electrical panel where the breakers are. The electrician I know suggested that but I thought it might be a bad idea. Now it's not sounding so bad.

3: I talked to a very nice guy who owns and operates an RV place and he said he's been using generators himself for many years. What he would often do to give the generator a path to earth is just use a large nail stuck into the ground connected to the generator's ground terminal by a piece of wire. I suggested a big steel tent stake.

He said the worst I'd ever feel is a light tingle when I step out onto the ground and that the idea of the skin of the trailer becoming energized enough to kill someone is pretty much nonsense. I suppose it COULD happen if there is some *MAJOR* wiring flaw or breakers that aren't tripping but otherwise, I don't see how that could happen like someone online told me who was preaching that I need to drive an 8' grounding rod every time I use the generator. The guy who told me that said he saw a kid get killed by touching someone's RV that was hooked up to a generator without a grounding rod.

Regarding GFCI, I think I will do like I had planned. Invest $15 in a GFCI adapter for the generator and use it whenever I run the generator. Sure can't hurt. Worst thing that it'll do is trip often with use of certain appliances. If I find that it's a problem on certain appliances, I will limit use of the GFCI adapter or the appliance that causes the tripping. Anything going wrong after the GFCI adapter will trip it meaning the extension cord and anything in the trailer, just not within the generator I guess.

I plan to use a UPS with AVR (automatic voltage regulation) on it for sensitive electronic devices such as my laptop, TV, etc so the devices will have adequate under/over/surge current protection in addition to backup battery power if the generator stalls for some reason or an RV park has lousy electrical service. Also I will be getting a plugin voltage monitor so I can verify the generator is outputting proper voltage.

Cubey

Are you going to plug the cord from the interior panel into the generator?

jwelectric said:

Cubey

Are you going to plug the cord from the interior panel into the generator?

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Yes, more or less. The side of the trailer has a male 3 prong 120v hookup inside of a weather proof cap that opens to plug in an extension cord and spring closes when it's not. This is how the trailer was designed. That leads directly up to the breaker panel in the trailer and the outlets and lights in the trailer come off of the breakers. The ground (3rd prong) in the panel is connected to the chassis of the trailer and that is also by design. However they didn't bond neutral/ground the breaker panel in the trailer which is correct. But if I can't find anyone to bond the generator, bonding the breaker panel in the trailer would at least be some better than no bonding at all. However, it would then always be bonded when I plug into grid power unless I modify the trailer's panel every time I switch between the two which seems like nonsense.

Cubey said:

jwelectric said:

Cubey, Are you going to plug the cord from the interior panel into the generator?

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Yes, more or less.

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Here in lies the problem.
If the generator is going to supply the panel inside the RV then Parts II and III of Article 551 will apply.

If you are dead set to do as you have seen others do and install this generator outside on the ground it is necessary that you have a full understanding of the bonding and grounding procedures for the interior wiring of the RV.

In Article 250 we find 250.20 Alternating-Current Systems to Be Grounded.
Alternating-current systems shall be grounded as provided for in 250.20(A), (B), (C), or (D).
This section clearly states that any AC system is to be grounded. What is grounded?
Grounded. Connected to earth or to some conducting body that serves in place of the earth.

If you were connecting to the RV park site pedestal that system will be grounded somewhere along its path whereby the interior wiring system would be grounded.

By installing a generator to supply the power to the RV and the fact that the generator is portable and will be a separately derived system meaning that there is no physical connection to the power source of the RV park then 250.34(C) will mandate the installation.
250.34 Portable and Vehicle-Mounted Generators.
(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be bonded to the generator frame where the generator is a component of a separately derived system.

FPN: For grounding portable generators supplying fixed wiring systems, see 250.20(D).

250.26 Conductor to Be Grounded — Alternating-Current Systems.
For ac premises wiring systems, the conductor to be grounded shall be as specified in the following:
(1) Single-phase, 2-wire — one conductor
(2) Single-phase, 3-wire — the neutral conductor

There has been much talk of walking around barefooted and even a mention or two of standing in a puddle of water barefooted along with this floating neutral.

When the neutral is left floating in a generator there is no neutral. Both conductors supplying the 120 volt circuit have the same value.
By bonding the neutral point of the generator to the frame and bonding the grounding terminals of the panel to this same point, a low impedance path has been established that will facilitate the operation of the overcurrent devices in the panel which will not happen with a floating neutral.

Now let’s get out of the puddle and off the ground and go inside the RV. With a floating neutral in the generator it wouldn’t matter which conductor, either the white or black that came in contact with any metal the inside and outside the RV will elevate the potential of 120 volts above zero.

Now that we have established that without the bonding to the frame and a faulted condition in the RV we will have any and all metal that is properly bonded at a potential of 120 volts above zero let’s also take a moment to think about a lightning strike.
During a lightning strike we do not have any physical connection between the cloud and the earth. What we do have is one being at a higher potential than the other thus a lightning strike. Your RV is just as this cloud and the earth, the RV will be at a potential of 120 volts above anything around. With something as simple as flipping a light on and you come in contact with the metal 6/32 screw that holds the cover plate in place could be fatal.

Now I shall leave you to handle this generator as you deem fit and how ever you think is safe.
I have given you the code references and tried to explain how they would affect your installation. Remember that the NEC is a bare safety standard and to do anything less is to be below the minimum safety standard.

jwelectric said:

By installing a generator to supply the power to the RV and the fact that the generator is portable and will be a separately derived system meaning that there is no physical connection to the power source of the RV park then 250.34(C) will mandate the installation.
250.34 Portable and Vehicle-Mounted Generators.
(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be bonded to the generator frame where the generator is a component of a separately derived system.

FPN: For grounding portable generators supplying fixed wiring systems, see 250.20(D).

250.26 Conductor to Be Grounded — Alternating-Current Systems.
For ac premises wiring systems, the conductor to be grounded shall be as specified in the following:
(1) Single-phase, 2-wire — one conductor
(2) Single-phase, 3-wire — the neutral conductor

Click to expand...

What about the idea of just bonding neutral to ground in the trailer's panel and then bonding the ground terminal on the generator to the generator's frame?

That would basically do the same thing as bonding the generator's neutral to ground and then bonding that to the generator frame. Only difference really would be the trailer would be bonded at RV parks as well unless I remove the bonding screw every time I switch between RV park and generator.

Here is a diagram I have created to illustrate what I mean:

Red=hot, blue=neutral, green=ground

Only thing I should point out about the digram that it is slightly incorrect is that I would be bonding ground on the generator to the frame at the external ground terminal, not at the outlets/panel.

Cubey said:

What about the idea of just bonding neutral to ground in the trailer's panel and then bonding the ground terminal on the generator to the generator's frame?

That would basically do the same thing as bonding the generator's neutral to ground and then bonding that to the generator frame. Only difference really would be the trailer would be bonded at RV parks as well unless I remove the bonding screw every time I switch between RV park and generator.

Here is a diagram I have created to illustrate what I mean:

Red=hot, blue=neutral, green=ground

Only thing I should point out about the digram that it is slightly incorrect is that I would be bonding ground on the generator to the frame at the external ground terminal, not at the outlets/panel.

Click to expand...

NO! NO! NO!

250.34 Portable and Vehicle-Mounted Generators.
(C) Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be bonded to the generator frame where the generator is a component of a separately derived system.

The words grounded conductor in (C) is referring to the neutral and it MUST be bonded to the generator frame.