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

[Joel_T]

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?

[wa8yxm]

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]

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]

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]

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]

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]

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]

SoundGuy wrote:
Where do I fit into this? :h :h

Aren't you the guy pounding your head?

[SoundGuy]

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]

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]

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

[wa8yxm]

Ok the reason you need an earth ground when hooked to shore power but NOT when using a generator or inverter.. That is the real question, how come?

Simple.. At many many points the NEUTRAL in your SHORE POWER system si bonded to ground.. In fact at one time, due to metal shortages, they ran a single wire from the pole to your house.(the hot lead) and relied on the Ground to act as the "Return" IN SOME PLACES THEY STILL HAVE HOUSES WIRED THAT WAY.

So imagine you are holding oh, say a hand grinder (Skill to be specific) and there is a hot-case short.. Now YOU become a return path when hooked to shore power.

BUT if you are running off the inverter, or generator and it is NOT bonded to earth ground, Then using that self same hand grinder.. You would be protected,, Because you are NOT a return path, there is no "path to ground" at either end.

Why did I choose a skill hand grinder? Used one professionally for a bit. It had a case to hot short.. I had to wear gloves to use it (Got my own Dremel (low end) to use in it's place. Dang thing lasted 20 years before it smoked Still have a Dremel here).

But the reason a earth ground saves lives when on shore power is because it shorts the current to ground (if there is an internal short) and blows the fuse/breaker instead of the user.. BUT if on Generator or inverter. There is no path to or from the ground so you are protected by "Double Insulation" technique (Which is used on many brands of tolls with plastic houses and 2 wire plugs)

[Chris_Bryant]

Joel_T wrote:
I've been told AC always needs an earth ground, DC not.

Strictly speaking, this is incorrect. The earth ground is actually a safety ground, and not required if you have ground fault interrupters.

"It's against NEC code for the trailer to have neutral and ground bonded together." ....and yet all trailers do?? Morningstar requires it for their inverter? What do they say?

First, no RV has neutral and ground bonded- the only place it will be is if it has on board power source. The inverter is a power source, as are generators. The neutral and ground are bonded *at the source*, but when you disconnect and go to shore power, they must be separate.

[Dusty_R]

NORM WADDELL wrote:
This is NOT to answer your question, but it might interest you.

Navy combat ships do NOT ground any system. The reason
is that, with our 'normal' HOUSEHOLD grounded systems, if the HOT
wire touches ground the breaker trips or the fuse blows. In combat,
this is obviously NOT acceptable !............in place of the grounded
system, a GROUND DETECT system is used to detect grounds, and they
are removed as soon as possible.

I have long thought that this should be extended to homes and businesses.

I've often felt the same, but too many would never get fixed because it still worked.
Factories used to use an isolated system with their 480v 3ph buss duct, but even there it often did not get repaired.

Dusty

[SoundGuy]

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. 😉