I've been told AC always needs an earth ground, DC not. An AC earth ground, as opposed to a DC type chassis ground, saves lives. To run any 120v stuff in an RV, the shore cord is supposed to provide that earth ground. When I plug that shore cord into a generator or invertor I don't have an earth ground. (I “may” have a bonded neutral to ground. How’s that safe? Seems that'd still be dangerous if there was a short.) When I plug into that unbonded generator or invertor I have to "bypass" my EMS device because it appropriately gives an open ground error. One of my invertors (Morningstar) doesn't even have an AC ground output terminal...just a hot and neutral, with neutral to be sent to a DC "earth" ground. RV's don't have an earth ground. When camping why shouldn’t I need a relatively short earth ground rod to attach to the RV's chassis ground and/or generator ground lug. Then I read neutrals are aren't supposed to be sent to chassis grounds just earth grounds. WTF! I'm not an electrician and would love a safer understanding of all this. Is there one?

When connected to shore power you have ground protection thru 'ground' lug and back thru power pedestal.When connected to generator it acts like an isolation transformer. Since the power source is isolated, there's no way for part of the current to flow back to the source through the ground and there's no shock hazard from the voltage to ground.

it Real Simplethe utility power is connected to earth groundtherefore circuits connected to utility power need an earth ground as a safetyif something shorts in an appliance or device, and earth ground completes the circuit and trios the breaker, rather than the device/appliance/tool being electrically HOT and you being the ground to complete the circuitthe RV genset or portable genset, is NOT connected to earth ground, if something shorts in the RV there is NO electrical circuit between RV and earth or portable tool/appliance and earth so power cannot flow between RV or tool and you to the ground and back to the generatorbut it can with utility powerRV genset or portable genset is "isolated power"if you want to drive a 10ft ground rod and ground your generatorgo ahead and do so, but you are safer with out it

This is NOT to answer your question, but it might interest you.Navy combat ships do NOT ground any system. The reasonis that, with our 'normal' HOUSEHOLD grounded systems, if the HOTwire touches ground the breaker trips or the fuse blows. In combat,this is obviously NOT acceptable !............in place of the groundedsystem, a GROUND DETECT system is used to detect grounds, and theyare removed as soon as possible.I have long thought that this should be extended to homes and businesses.

My first thought is that it's a compromise. It would be ideal if an RV's frame and skin was always earth grounded. More developed campgrounds provide this via the shore connection. For less developed campgrounds they could provide ground connections at each site, with a lot of cost to install and maintain them. When moving down the road an earth ground is obviously impractical. So the code allows the vehicle frame to "act" as the earth ground. What about shock risk? Shore power always has one of its conductors earth grounded, so an accidentally hot frame or skin could give a full-blown shock. Earth grounding is therefore important when on shore power. The portable or vehicle mounted generator has all of its conductors isolated from earth ground, so there should be no current path for a shock to earth ground. There is sometimes a conduction path from the vehicle frame to ground, so the vehicle frame may or may not be connected to some degree to earth ground. If the generator isn't bonded, there's no current path to earth ground. If it is bonded, any current path from the frame to earth ground will put them at the same potential, meaning no current path for a shock.

There should be a sticky for this question. A search will show lots of threads.The short answer, shore power is referenced to ground. Portable generators or inverters have no reference to ground. They don't even have a neutral. They have two wires, either one could be defined as "Hot" or as "Neutral". You could bond the "neutral" to generator chassis/receptical ground. It won't make the MH any safer. In fact, the MH will become less safe. With no bond, it takes two faults to get shocked. It takes just one fault to get shocked when bonded.

Why don't RVs need an earth ground for AC circuits

wa8yxm
Explorer III
Oct 12, 2015
Let me draw you a picture:

Shore power.. Your useing a hand drill and it shorts hot to case the 3rd wire is broken off (of course) so you could plug into a 2 wire outlet at home:

Transformer---Stuff---Hot wire-----case/YOU---_Ground---Return to transformer (Been nice knowing you) Stff is your meter, breaker box, and so on but for this it's all part of the hot wire.

now let's use the generator (or inverter) to power that same shorted drill

Hot wire----Case/You---Ground (Tthat is all folks there is no return path to the generator/inverter you are protected and continue to breath.. In fact the drill works normally and you finish the job.
ktmrfs
Explorer II
Oct 12, 2015
Huntindog wrote:
Thkis has been interesting.

I would like to pose another somewhat related question... What about running a generator in the rain?

I have seen quite a few people do this... It scares the bejesus out of me. I always rig some sort of rain roof over mine,,, but now I wonder if I am being too cautious and maybe those I see doing it know something i don't?

I, along with lots of folks I know in western oregon do this quite often with honda/yamaha's w/o any rain roof, so far no issues. And really the risks are very very minimal and highly unlikely to cause a problem. It's a double insulated system.

However, for those that are concerned and make a rain cover, I can understand the conern, and if it makes one confortable, take that route.
One thing I would say to never, ever ever do is put a running generator under the trailer to keep it out of the rain. Good way to end up with carbon monoxide poisoning.

Now an open frame generator with a ground/neutral bond, that I would be concerned about in the rain.
Huntindog
Explorer
Oct 12, 2015
Thkis has been interesting.

I would like to pose another somewhat related question... What about running a generator in the rain?

I have seen quite a few people do this... It scares the bejesus out of me. I always rig some sort of rain roof over mine,,, but now I wonder if I am being too cautious and maybe those I see doing it know something i don't?
Bobbo
Explorer II
Oct 11, 2015
Why should electricians agree.

Doctors don't agree, that is the reason for second opinions. And thirds.

Name ANY technical area, and the experts will disagree.
Joel_T
Explorer
Oct 11, 2015
Hey, don't be sorry... I much appreciated the link. Not so much the apparent lack of a "right way" from electricians that obviously have gone to different schools. :B??
SoundGuy
Explorer
Oct 11, 2015
SoundGuy wrote:
Where do I fit into this? :h :h

Salvo wrote:
Aren't you the guy pounding your head?

Over what? :h My only involvement in this discussion was to offer a link to another discussion which covers the very topic the OP asked about - why don't RVs need an earth ground for AC circuits? Anyone stubborn enough to plow through those 41 pages of discussion will discover that even those well versed in this topic couldn't agree on a definitive answer ... and if they can't I doubt the OP is going find his answer here in this discussion. Regardless, this has nothing to do with me ... sorry I bothered trying to help the OP or anyone else who may be interested in the subject by posting that link. :R
Salvo
Explorer
Oct 10, 2015
SoundGuy wrote:
Where do I fit into this? :h :h

Aren't you the guy pounding your head?
SoundGuy
Explorer
Oct 10, 2015
SoundGuy wrote:
Sure ... wanna read 41 pages of discussion on the subject of portable gensets, bonding, earth grounding, etc, then have at it ;) ... but don't expect to come away with any "safer understanding of all this" when even the "experts" who participated in that discussion can't agree! :S

Salvo wrote:
Stop pounding your head and think a little.

Why is there no bond (neutral to chassis) on navy ships?

It's a lot better to be two faults away from a catastrophic than one fault away.

Huh? What's my post that simply provides a link to another discussion about portable gensets, bonding, earth grounding, etc, given you cause to trash talk? Where do I fit into this? :h :h
ktmrfs
Explorer II
Oct 10, 2015
SoundGuy wrote:
ktmrfs wrote:
now this does cause an issue with those of us using a portable generator with an EMS system that will shut down with an "open" ground, which is what it will detect since a portable generator in compliance with NEC as a portable device doesn't have a neutral/groud bond. There are mutliple solutions, one common one is a plug with the neutral side shorted to the ground side and plugged into one of the outlets on a duplex outlet, thereby making the EMS think there is a neutral/ground bond.

OK, I'll bite ... what are all those "multiple solutions" you're referring to? :h The only practical solution I know of when an EMS interprets a genset's floating neutral as an "open ground" and won't output voltage to the RV is to bond the genset's neutral to it's ground. Enlighten us. ;)

Yes, That's about the only practical solution IMHO.

another is to simply turn the progressive industries EMS portion OFF when using a generator. It's still gives surge protection and undervoltage protection, just not reverse polarity protection, frequency protection etc. And one could argue the EMS really isn't nearly as critical when hooked to a generator vs. plugging into a pedestal.

progressive industries, makers of EMS solutions outlines one other solutions as well, or at least at one time did. Not very practical, so I don't even remember the details.
Salvo
Explorer
Oct 10, 2015
Stop pounding your head and think a little.

Why is there no bond (neutral to chassis) on navy ships?

It's a lot better to be two faults away from a catastrophic than one fault away.

SoundGuy wrote:

Sure ... wanna read 41 pages of discussion on the subject of portable gensets, bonding, earth grounding, etc, then have at it ;) ... but don't expect to come away with any "safer understanding of all this" when even the "experts" who participated in that discussion can't agree! :S

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