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Portable inverter/generators?


Kirk W
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I have been doing some investigating of issues related to the use of a Honda 2000i which I recently acquired to complement our present travel trailer and while I have learned a few things about how it is built/wired, the result is more questions than answers. Since we have a couple of members on the forum with an electrical design background, how about an explanation of the reason that both Honda and Yamaha, and perhaps all of the inverter generator builders isolate the neutral and ground since that makes any of the line monitor devices see an open ground? In reading the owner's manual it states:

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GROUND TERMINAL
The generator ground terminal is connected to the frame of the generator, the metal non-current-carrying parts of the generator, and the ground terminals of each receptacle.
Before using the ground terminal, consult a qualified  electrician, electrical inspector or local agency having jurisdiction for local  codesor ordinances that apply to the intended use of the generator.

3

I can find nothing more on this but suspect that the intention is to tie that to a ground rod or appropriate earth ground. I had expected to find that instruction but didn't. 

One note, I have downloaded both the owner's manual and the service manual from Honda but found a much better owner service and operation guide from this link. 

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2 hours ago, Kirk Wood said:

...an explanation of the reason that both Honda and Yamaha, and perhaps all of the inverter generator builders isolate the neutral and ground since that makes any of the line monitor devices see an open ground?... suspect that the intention is to tie that to a ground rod or appropriate earth ground. I had expected to find that instruction but didn't...

Not sure if the RV market is the biggest market for the small inverter generators and what design changes might be required. Yamaha told me that their larger portable inverter generators that they recommend for running RV air conditioners had a bonded ground. The line monitoring systems that will not pass the current if the ground is open are fairly new. I believe there are still some in production that will identify the fault but still pass current.  With the old ones that would pass the current, Yamaha recommended either ignoring the fault warning or not using the device rather than using a ground bonding plug as recommended by some on the internet. My Yamaha 2400 has a ground lug on the front panel of the generator. The owner's manual clearly instructs that this should be connected to a grounding rod. I seem to recall that using the ground rod did not eliminate the code on the Surge Guard. I just stopped using it when connecting to the generator.

 

Edited by trailertraveler
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1 hour ago, trailertraveler said:

I seem to recall that using the ground rod did not eliminate the code on the Surge Guard.

I am pretty sure that it would not, as that just provides earth ground while the Progressive or Surge Guards both want the neutral and ground bonded at the source, as they would be for a shore power outlet that is properly connected. But the addition of a ground rod would remove any chance of the RV experiencing "hot skin" syndrome. Using an ohmmeter I tested between the ground pin on the generator's 120V outlet to the ground screw and it is connected. Reading the service manual, that screw is connected to the metal frame of the generator so it is the common ground. I think that if I had a metal water hydrant, I would connect a jumper between it and the screw, but most cases that probably wouldn't be available. 

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Isolated power (no connection between the generating source and ground) is often used in places like operating rooms where even a slight amount of leakage current could be fatal.  Power outlets feeding medical equipment are fed from isolation transformers where the secondary feeding the outlet is completely isolated from ground.

The small generators that do not bond their power to the chassis ground operate in the same manner.  As long as the isolation remains intact, there's no way you can get a shock between ground and either of the output wires, since there's no path from ground to the power source.

This also eliminates the possibility of a hot skin, regardless if the skin is floating free or if it is tied to a ground rod, since there's no way for current to flow from an isolated source to ground.  It's the same principle that lets a bird perch safely on an energized high voltage line.

Tying one side of an isolated source to the ground pin actually increases the shock hazard, as now anything that's connected to the ground pin has a current path back to the voltage source.

There's nothing wrong with isolated power, the only reason to tie power to ground is when the capacitance and other leakage sources become too large to let the power source remain fully isolated.

Edited by Lou Schneider
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Kirk, now that's one EXCELLENT question. As a salty old electrical tech I'm sure you understand all this, however, the whole topic of Grounding and Bonding and Floating versus Bonded Neutrals is the MOST MIS UNDERSTOOD subject I’ve found in the RV users community. You know it’s next to impossible for an attorney and engineer to keep it simple lol and I try my best, but it’s a complicated issue and NOT in my DNA to be brief.

 Let me begin by noting what I call "earth grounding" of the Neutral IS NOT THE SAME AS bonding the Neutral to Ground. Earth grounding the Neutral is for lightning and surge protection and to keep the grid at one common low voltage reference IE Mother Earth.

 LET ME PUT MY ATTORNEY HAT ON  I think one reason many small portable gensets float the Neutral is the corporate lawyers and engineers consider it safer for the know nothing Billy Bobs and Bubbas who use and don’t understand electricity versus big gensets (have Bonded Neutrals) where professional electricians install them. In fact, for small portable construction site gensets that serve plug and cord connected tools via onboard mounted receptacles, OSHA considers earth grounding as HAZARDOUS (IE NO earth ground rods to be used). I have the link to the OSHA Professor that explains all that somewhere, I will post it later. Also similar to Lou’s good discussion, if the genset has no connection to mother earth (isolated floating system) if your barefoot on wet ground grandchild touches a hot genset feed wire he doesn’t get electrocuted.  An isolated system is just safer for Billy Bob and Bubba and their grandkids and that’s why I think many manufacturers float the Neutral on small portable gensets. The instructions on gensets have the catch all Ground per the NEC which I'm sure the lawyers insist upon but they don't provide much if any detail as there are just too many variables and different installations which require different configurations. 

 WITH MY ENGINEERS HAT ON there are times when a floating Neutral is preferred and there are times when a bonded Neutral is preferred, one of which has to do when Billy Bob wires a portable genset to backfeed his home supply during a power outage. To save a few bucks on a 120/240 volt single phase three wire system he can get by with ONLY a cheaper 2 pole transfer switch to switch the Hots but NOT the Neutral in which case the genset requires a floating Neutral, unlike a 3 pole transfer switch in which case the Neutral is switched also, but the genset then requires a Bonded Neutral (it becomes a Separate Derived Source just like a utility transformer requiring bonding to a grounding electrode). Then there’s the whole topic of single point grounding and separate derived sources and proper transfer switching methods and the fact the RV panel has separate and isolated Neutral and Ground Busses on and on but that’s for another thread.

 NO, if the genset has a Floating Neutral driving a ground rod isn’t gonna make an EMS think all’s well.

 Of course, as yourself or Jack ?? has posted pictures and explanations of how to wire a plug with Neutral and Ground connected to easily create  a Bonded versus the factory furnished Floating Neutral, it’s pretty easy to cure the problem if needed.  

 SAFETY AND LEGAL LIABILITY is one reason for Floating versus Bonded Neutrals and engineering is the other, but that’s wayyyyyyyyyyy to complex to get into on here, although I’m glad to open that can of worms and provide an explanation if needed.

 Best wishes, that’s as brief as possible for an attorney engineer lol

 

 John T

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1 hour ago, mptjelgin said:

Really good article here about dealing with this situation, with a simple and practical solution:

mpt, yeppers that's the picture that's been posted here before by Kirk or Jack if I recall, cheap simple and sooooooo easy to create a Neutral Ground Bond in small gensets that have Floating Neutrals. You just take a plug and run a wire from the Ground terminal over to Neutral and stick it in an unused outlet..............

 

John T

Edited by oldjohnt
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6 hours ago, Lou Schneider said:

Tying one side of an isolated source to the ground pin actually increases the shock hazard, as now anything that's connected to the ground pin has a current path back to the voltage source.

I know that you are right, but I'd not thought of that aspect. I wonder why some of the manufacturers suggest doing so? With that in mind, I think a better bet might be to run a jumper from that ground post on the generator to a solid contact on the frame of the RV. That would definitely eliminate any possible "hot skin" problems. Thinking of it, an onboard generator set like most motorhomes have today is pretty much the same when in use as the jumper between the portable generator's chassis and that of the RV, except if shore power is connected and with most RVs the ATS will disconnect the generator when shore power is connected. In fact, it used to be very common for a motorhome to have a power plug that was supplied by the generator which the shore power cord plugged into for storage of generator use. 

While my Honda 2000i has the ground point on the power outlet area and it is labeled as ground, the owner's manual never mentions it and the service manual does so only to state that it is connected to the chassis and all metal parts of the generator set. 

2 hours ago, mptjelgin said:

Really good article here about dealing with this situation, with a simple and practical solution:

I am a fan of the No Shock Zone, but I'm not sure that is the best solution unless you happen to be unwilling to operate without the TRC/Progressive line monitor device, or if yours is hardwired inside and thus not easily worked around. I have considered the solution they suggest there. 
 

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33 minutes ago, Kirk Wood said:

In fact, it used to be very common for a motorhome to have a power plug that was supplied by the generator which the shore power cord plugged into for storage of generator use

That's right Kirk, in that situation if you take the RV power cord and plug it into an outlet fed by the onboard Generator, you are switching BOTH the Hot(s) and the Neutral. In that situation the onboard genny has a Bonded Neutral and is considered a "Separate Derived Source" similar to how when you're plugged into the utility where the single point Neutral ground Bond has been established.

 

33 minutes ago, Kirk Wood said:

While my Honda 2000i has the ground point on the power outlet area and it is labeled as ground, the owner's manual never mentions it and the service manual does so only to state that it is connected to the chassis and all metal parts of the generator set. 

That's what Id expect in a Floating Neutral genset. The thing is if you want to use it to backfeed your homes panel during a power outage and you don't switch the Neutrals, the genset needs a floating Neutral HOWEVER the case frame of the genset, like any other non current carrying metallic enclosure, needs a bond to the Equipment Ground Buss just like it was a junction box and that post/terminal provides a location for such. IE it serves a purpose indeed !!!

 

33 minutes ago, Kirk Wood said:

I am a fan of the No Shock Zone, but I'm not sure that is the best solution unless you happen to be unwilling to operate without the TRC/Progressive line monitor device

 That may or may not be the absolute "best solution" but if one doesn't like the monitoring device to throw that error code, that solution works and is actually not much different then if you had an onboard genset that already had a bonded Neutral. I see MANY in the RV community that use that solution while others do not ITS YOUR OWN FREE CHOICE

PS seems like it was you or Jack or Yarome that posted the picture before showing the Neutral to Ground pigtail solution an a plug, WAS THAT YOU OR ANOTHER GENT ?????????????????

 

Great discussion Kirk, and like I said EXCELLENT QUESTION you asked, hope this helps you, take care now.

John T Longggggggggg retired electrical power distribution design engineer and rusty on this stuff so no darn warranty LOL  

Edited by oldjohnt
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18 hours ago, Lou Schneider said:

There's nothing wrong with isolated power,

 Lou,

  While it may not be as widely used now, when I designed power distribution in heavy industry 240 and 480 Volt 3 phase 3 wire floating Delta systems were fairly common. I preferred a grounded system and installed a CORNER GROUNDED DELTA in one building.

 

Kirk, you posted to me  "You do realize that I'm not an electrical amateur? :wacko: 

 

  YES I do indeed, that's why I posted this (see below what I said earlier) and I appreciate all your help !!!!!!!!!!!!

 

 "As a salty old electrical tech I'm sure you understand all this"

 

   

8 hours ago, Jack Mayer said:

Kirk,  HERE is something I wrote some time ago that addresses aspects of this.   You may or may not find it helpful. I think some or most of it has been covered here. 

 

  Jack,  Excellent information, I already had that linked and saved in my archives, good reading for sparkies.

 

 Kirk, and others additional FYI,

 If you notice and even look at ads for small portable generator use, you see families and kids setting outdoors maybe having a picnic or camping etc and they are running small portable appliances and electronics fed by the generator. Those loads operate if there's 120 VAC across Hot and Neutral AND DONT NEED OR CARE OR EVEN KNOW if the energy source Neutral is floating or bonded, there's no reason why it MUST BE BONDED. Again if your barefoot grandchild on the wet grass accidentally touches a hot wire from a floating generator system,  he or she doesn't get shocked. That's UNLIKE the utility grid where earth grounding of the Neutral is for lightning and surge suppression and maintenance of a common low voltage potential, while there's GFCI protection required in outdoor applications. In the alternative, if you take that portable genset and create a grounded system and the Neutral has a connection (albeit resistive) to mother earth and wet grass  and your grandchild accidentally comes in contact with a hot wire from a damaged cord that was ran over on sharp rocks or is submerged in a water filled ditch etc.,  HE OR SHE CAN GET SHOCKED !!!!!!!!!!!!!!!!!!!!!!

  You asked about floating system portable generators and hopefully in this discussion and the advice from the fine gents above both yourself and others have gained some insights to perhaps why Honda or Yamaha manufacture small portable generators with Floating Neutrals.

 Best wishes, God Bless and thanks to all above.

 John T   

Edited by oldjohnt
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8 hours ago, Jack Mayer said:

I don't consider myself an expert on grounding issues. But perhaps this will help a little.

Great article! Which brings a question.... If there is a label listing my Honda as floating ground, I haven't noticed it but I guess I'll have to take a look. But you then agree with the "No Shock" guys and a step more in saying that you shouldn't use it without the plug that they suggest? Interesting as that seems to disagree with what Lou is saying about isolated circuits such as in a hospital. The bonding plug would clearly be easier to use than a jumper as I was toying with between the chassis ground on the Honda and the frame of the RV. 

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2 hours ago, Kirk Wood said:

as I was toying with between the chassis ground on the Honda and the frame of the RV. 

  Kirk, FYI, if the generator has a Floating Neutral and the RV is setting there unplugged and remember its Panel has NO Neutral Ground Bond, BOTH the generators iron frame and the big RV frame are just two hunks of iron NOT connected to the generators electrical system and connecting the generators iron frame to the RV iron frame has no real effect on the generators "electrically" floating Neutral, IE its still floating, still neither hunk of iron is bonded.

 Use of an isolation transformer in a hospital (sterile indoor space) isn't quite the same as why small portable gensets (often outdoors on mother earth) float their Neutral. If you're outside on wet ground for safety there's really no need why the genset needs a bonded Neutral for the reasons I described above (and also see why below) .

 Sure, bonding the Neutral can cure fault codes on sensing devices, but there are reasons and conditions whereby it could possibly be safer to leave a portable genset floating as it came from the factory. Sure it still works if you create a bond.

NOTICE TO ALL here is a good article describing how where and why grounding of portable generators CAN BE HAZARDOUS, that may have something to do with Kirks good question regarding WHY Honda and Yamaha float the Neutral !!!!!

 http://manualzz.com/doc/18583037/portable-generators-and-osha-construction-regulations

Fun discussion, hopefully helpful and informative, keep the questions coming. I look forward to Jack and all the other fines sparkies answers and comments............. 

 

 John T

Edited by oldjohnt
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1 hour ago, Kirk Wood said:

If there is a label listing my Honda as floating ground, I haven't noticed it but I guess I'll have to take a look.

 Kirk, I'm sure you ALREADY know this, but FYI for some who may not, use an ohm meter or continuity tester to see if there's a low resistance connection between the generators iron frame and Neutral at the receptacle PIECE OF CAKE...

John T

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1 hour ago, NoDirectionHome said:

I consider Randy and oldjoint as the go-to guys on this subject.  As a mechanical engineer, a BIG THANK YOU to both for your contributions.  -Steve

Thanks for the kind words and you're sure welcome Steve. Unfortunately I'm long retired as a power distribution design engineer and rusty on this stuff grrrrrrrrrrrrrrrrr and couldn't pack water to the more experienced electrical savvy gents here, but hey I do try my best to help when I can.

John T

Edited by oldjohnt
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  Thanks Jack, good information, I've never had the pleasure to speak with Randy, but Joe McPartland (E C & M, Electrical Construction and Maintenance Magazine) and Mike Holt were the ones who knew more about grounding then anyone I ever talked to, they were also GREAT teachers, best I ever had. I'm pretty sure both served on the NEC board at the time. 

http://www.mikeholt.com/

 Great informative thread going, thanks to Kirk who asked the question and all contributors. 

 John T

 

Edited by oldjohnt
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I don't claim to be an expert and it seems that even those that do can not agree. This is from one of the write-ups linked to and praised as excellent:

Quote

A portable generator without N-G bonding really should not be used for an RV without bonding the N-G at it

and this is from another:

Quote

Repeating myself - I do not advocate bonding with a portable generator or inverter, period.

Since Yamaha was emphatic not to use a bonding plug on their generators that are not bonded, I am inclined to go with their guidance and continue to use their generator as they recommend.

Edited by trailertraveler
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22 hours ago, NoDirectionHome said:

I consider Randy and oldjoint as the go-to guys on this subject.

 

18 hours ago, Jack Mayer said:

Randy knows more about grounding issues than anyone I have ever talked to.  

And he also has a very rare combination as both an engineer and an electrician. He also seems to have the ability to communicate with non-engineers which is a very rare thing. Since I do not own and have never owned an HDT, this is the first that I have seen of his writing so I sure do wish that discussion had been in the technical forum! 

Quote

That’s it.  Wire the generator or inverter through a transfer switch just like shore power is wired but add a GFCI which will disconnect power in no more than 6/1000th of a second if a fault occurs.  Much, much faster than a circuit breaker - even a magnetic breaker.

 

If I read this accurately, he would not connect an RV that has no transfer switch to an inverter/generator? I'd not thought of the GFI but will look into building a box for that, but Jack said he uses the bonding plug yet Randy seems to disagree? It looks to me as though it might be better to make bonding device, if used, one that also includes the GFI? Better yet, someone see if Randy might join in this thread........

Edited by Kirk Wood
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