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Old 05-25-2012, 12:52 PM   #15
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I'm with you - why would there need to be any other forum than this one?
I'll warn you though, they're not as nice to one another as we are over here!
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Old 05-25-2012, 12:54 PM   #16
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Soyboy, you're asking the same questions I have, and I think a lot of folks have. I don't get it either.
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Old 05-25-2012, 01:58 PM   #17
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Soyboy, you're asking the same questions I have, and I think a lot of folks have. I don't get it either.
I don't think anybody has all the answers. I may end up confusing myself if this keeps upů The important point to remember in all this is, you want to make sure the current never flows through a human body. It can flow wherever else it likes, as long as it's not through you or your loved ones.

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How is having a generator mounted in an RV different than using an external one?That is in the sense of grounding. I would assume with an RV and an internally mounted generator it would have something to do with the chassis of the genny being directly connected to the chassis of the vehicle (bonded?). But if there was some sort of insulation failure, couldn't the RV chassis become hot and then cause a shock hazard if one touched the vehicle and "earth" at the same time? If that is the case, then shouldn't that vehicle be grounded to "earth" just like a portable?
Because of the bonding, the chassis is the point of lowest common electrical potential. Current flows from higher electrical potential to lower leelctrical potential. You could energize the chassis in the case of current leakage, but as long as you're already in the RV, your own body is not part of the circuit. Now, if a plug-in device malfunctions, and you're holding that device, the leaking current tries to go from the device to the chassis, through you. That's why we have GFCI.

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Does the fact that it is a floating ground and that the vehicle and the generator are "directly" connected, chassis to chassis eliminate the possibility of a vehicle to "earth" shock hazard.
Yes. As long as the generator is bonded to the chassis, any current leakage from the generator stays within the generator/trailer system; it doesn't go anywhere else. It's different when you're connected to shore power, but I won't explain the diference here; that will just make a confusing issue worse.

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If that's true, I guess the hazard with a portable generator hooked to an RV, on a tailgate or on the ground is that the chassis of the two (gen and vehicle) are not bonded?
Trailer and generator are bonded through the umbilical's ground wire. As long as the trailer itself is not grounded to earth anywhere, the generator doesn't need to be, either. Even OSHA says that.

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They are only connected by the neutral and hot wires?
Not quite sure what you mean by this one.

Even if you hitch the truck to the trailer, the truck does not share the trailer's ground bus. Current leakage from the generator may not go through the ground wire in the umbilical; it may go through the generator's frame and energize the truck; depends on just where the leakage occurs.

If it energizes the truck, it can energize you when you touch the truck.

Quote:
But what about the "ground wire, I assume that is connected/bonded to the chassis of the portable generator so, then wouldn't the ground wire in the trailer also be connected to the trailer chassis, and that in turn created a bond between the vehicle and generator (as long as the ground was good).
Truck and trailer DC systems are bonded together by hitching up the trailer to the truck, but not the AC systems; the truck is still isolated from the rest of the AC system, until and unless current leakage from the generator energizes it.

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Of course maybe that is what we are protecting....the circumstance where, for some reason, the ground goes away.
Not so much where the ground goes away, but where there's damage that causes the ground to be somewhere it's not designed to be. And in all cases, what we're protecting is human life, by making sure no one accidentally becomes a conductor in an electrical circuit.

Does this help, or make things worse?
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Old 05-25-2012, 02:07 PM   #18
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Sorta....till I start thinking about it again!
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Old 05-25-2012, 02:22 PM   #19
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Thanks Pro: gotta run now (going camping this weekend)...I might hit you up with a few more fine points later!
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Old 05-25-2012, 03:58 PM   #20
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As a safety professional in the construction field I will weigh in too...it depends.

Our COMPANY policy is you ground all generators.

OSHA basically says "Ask MOM" MOM being the Manufacturer's Owners Manual.

We have about 30 generators in the field at any given time. I have done an exhaustive review of ALL the owner's manuals. With a few notable exceptions of older units none of the them require grounding unless required by local code. I have worked on projects where they had to be grounded by a licensed electrician, other projects we could ground our own, on others yet no one cared what you did.

Personally I ground mine if at all possible to minimize risk.

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Old 05-25-2012, 05:57 PM   #21
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Pro,
Very well said.
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Old 06-05-2017, 04:51 PM   #22
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AC Ground

Protagonist:

I appreciate all the excellent info, but it seems the more I read the less I know...

So the 120V AC comes into the inside 120V breaker box from the exterior shore PWR panel. As I understand it the ground goes to the ground bus, the Neutral goes to the neutral bus and the hot goes to the rails via a lug or breaker.

From there the hot travels out through the breakers to appliances, sockets, lights etc, before feeding back to the ground bus.

When a generator becomes involved is the same true of the generator, so that the AC system essentially floats except for the shore power?

If an Inverter is added into the mix the hot goes into the interior 120V breaker box via a breaker, and the ground goes to the ground bus which it essentially shares with the shore, and the generator?

So that in the end the only ground is the shore power when it is connected??

While the DC floats completely separately using the DC- as ground so that in the end nothing attaches to the chassis of the trailer, but both AC and DC systems float, except for their link to shore power??

And one last question just to assure matters are as complex as possible- do you ground the solar panels and mounts / rails themselves to anything? I've seen some that have copper wire run to each panel and rail and then to the chassis, and some with no ground.

I appreciate your patience...

Thank You
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Old 06-05-2017, 05:30 PM   #23
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You are responding to an old post, and to my knowledge, Protagonist has been missing from here for a while, so I'll take a shot at your comments and questions.

"From there the hot travels out through the breakers to appliances, sockets, lights etc, before feeding back to the ground bus."
The current flows from the hot to the NEUTRAL bus (and back, since this is AC we are talking about). The GROUND bus should be isolated from the NEUTRAL bus.

"If an Inverter is added into the mix the hot goes into the interior 120V breaker box via a breaker, and the ground goes to the ground bus which it essentially shares with the shore, and the generator?"
The inverter connects to both DC and AC distributions. The wiring of the AC side varies. Some RVs have dedicated outlets for inverter power. Others may have transfer switches. The hot side goes through a breaker as you suggested to either the dedicated outlets or the transfer switch. The NEUTRAL goes to the NEUTRAL bus. If the generator has a ground terminal, it can be connected to the GROUND bus. On the DC side it connects to the 12V positive and negative terminals of the battery, typically directly through a dedicated breaker on the positive side.

"While the DC floats completely separately using the DC- as ground so that in the end nothing attaches to the chassis of the trailer, but both AC and DC systems float, except for their link to shore power??"
Not on my trailer. The battery negative is connected to the chassis and skin. Some loads use negative return wires, some use the frame. The AC ground (green wire safety ground) is connected to the chassis and frame. So the chassis of the trailer connects AC green wire safety ground and the 12V negative, but is isolated from the AC neutral.

Military standards (when I was designing communications shelters a few years ago) required that the shelters and deployed generators have a ground stake connected to their frame. While this may be good practice, it is seldom done in the RV world.

I can't answer your solar panel question from any experience base. Lew may weigh in on this. Connecting the solar panel negative line to the battery negative provides the return connection for the solar panels. I think safety practices, if not code, would suggest that the frame of the solar panels be connected to chassis ground in cast the positive side of the panel should somehow get shorted to the frame and present a shock hazard.

Sorry to be so long winded.

Al
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Old 06-05-2017, 07:14 PM   #24
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At jobs we had huge generators (semi sized) and portables; Honda 3000's. The main generators were always grounded with a copper ground rod pounded into about 6' of earth. The portable's were never grounded. (Not saying that's right, but it's what we did.)
We did run a ground wire from the equipment to a metal post, but that improved noise on the digital circuits, not for safety.

Keep in mind, if you're in a campground, driving a ground rod in could puncture water pipes and power cables just a foot under your campsite.

My Honda has a ground lug, but I'm planning on leaving it in the truck bed, so it's not grounded. Since both vehicles are sitting on rubber, I guess you could make a ground clip to go from the chassis to a water pipe. I've never seen it.

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The current flows from the hot to the NEUTRAL bus (and back, since this is AC we are talking about). The GROUND bus should be isolated from the NEUTRAL bus.
If you open up your breaker panel at home, I'll bet you'll find the neutral and grounds tied together. Mine is.
In theory*, Neutral and Ground are at the same potential.


* "In theory, practice and theory are the same. In practice, they are not." -- Yogi Berra
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Old 06-05-2017, 09:31 PM   #25
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Hi

First off, to "ground" the system, a 6' ground rod may or may not be enough. If you are out in the sandy desert, it will not do much of anything at all. If you are in rocky soil, you may need a pile driver to get it in and a back hoe to get it out again. I have never, ever seen anybody do this on an RV generator .. not ever.

On a standard electrical system, the ground and neutral do indeed get together. Pop open the box in the basement of your home and take a look. It's wired to the same code we're talking about on an RV. On a normal shore power feed, the connect point is in the (external to the trailer) box you plug in to. On most inverter generators that connection is missing. A good power monitor will spot this and yell at you ....

Bob
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Old 06-05-2017, 11:51 PM   #26
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The power panel in an RV is considered a "sub panel" in which the neutral and ground buss's are located. These 2 buss's are NOT connected or bonded and they should not be.
Unless you drive a ground rod (usually 8') and connect it properly it is a waste of time and effort.
Since the generator is considered "isolated" power unless you get between the hot leg and the neutral in most cases there is no risk of shock.
As with all AC electrical systems water (moisture) is the enemy. Safety should always be your first priority.
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Old 06-06-2017, 03:29 AM   #27
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Unless you are bringing you AC power out of the camper and doing something strange with it, dont worry about grounding the vehicle. Your best bet is to install gfi outlets. They will trip with or without the vehicle grounded when they sense that current is flowing to something other than the neutral wire
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Old 06-06-2017, 02:18 PM   #28
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Hi

Ok so here's the gotcha: The RV *assumes* the neutral and ground are bonded external to the RV (as they are with a normal shore power hookup). The inverter generator does not bond the two lines together (in general it should not). Essentially what you have is a gap between what one side assumes is true and what the other side assumes is true. Since this is a strange situation, there is no one simple answer about what to do. Your choices are to leave the neutral floating (at who knows what voltage) or to bond the two (and create a non-standard condition). My vote is to bond the two at a custom adapter that goes between the generator and the RV. The very real risk is that this adapter gets used somewhere else ... label it clearly !!!

Bob
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