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Author Topic: Grounding a portable generator  (Read 958 times)

StevieG

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Grounding a portable generator
« on: August 31, 2018, 09:56:39 PM »
Hi I new to rving and have recently purchased a new 17ft travel trailer. I also just purchased a 4000w portable generator. My question is if I need to ground it or not. The manual states to ground it so the GFIs work properly. Ive talked to some friends and they said they never have grounded their generator. Ive been searching the web and have noticed this is kinda a back and forth subject to ground or not to ground. Any thoughts would be helpful. Thanks
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blw2

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Re: Grounding a portable generator
« Reply #1 on: August 31, 2018, 10:34:33 PM »
I've asked that question before myself...and I've also seen it discussed here before.  Some electricians here that are sure to chime in so I won't speculate an answer why yes or why no because I really don't understand the ins and outs of it.

I'd say the vast majority of answers I've seen are that no grounding is necessary, and sometimes folks talk about it being even a bad thing to do (ground loops or some such thing)

Personally, I've never grounded one, have used several different ones, for odd jobs mostly (saws and tools).  I have a little generator I bought years ago for emergency prep.  I've never really used it, just ran it a few times.  When I bought it, I bought a length of heavy copper ground wire.  I figured that if I ever end up setting it up outside during an extended outage, I will probably connect it to the ground lug on the genny and stick it in the ground before I run cords into the house.  I know it's not a proper ground rod set up, but it seems to me having a path to ground is better than it finding a way through something else.
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Optimistic Paranoid

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Re: Grounding a portable generator
« Reply #2 on: September 01, 2018, 04:28:20 AM »
You absolutely do NOT 'ground' a generator in the sense that you 'ground' a house - by driving a rod into the ground and attaching the third, or safety ground to it.  What you MAY have to do is bond the ground and the return together.  Some generators come that way, many don't, the later is referred to as having an 'open' or 'floating' neutral.

There is a simple and inexpensive way to do this, and it requires no skills or modifications to the generator.  Buy one of these and plug it into one outlet of your generator.

https://www.microair.net/products/generator-bonding-plug?variant=12272654155860

For a fairly simple explanation, see this site:

http://www.progressiveindustries.net/single-post/2015/09/10/Testing-a-Generator-for-a-Floating-Neutral
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Re: Grounding a portable generator
« Reply #3 on: September 01, 2018, 04:43:11 AM »
sometimes folks talk about it being even a bad thing to do (ground loops or some such thing)

To steal a line from the old Highlander TV show:  "There can be only one!"

In your stick's and bricks, the neutral and the ground are bonded together in the main fuse box.  This is so the safety ground (third wire) has someplace to conduct any stray or leaking current to.  Without this bonding, it would provide no safety at all.

If you had a shop or barn or something like that on your property, and you ran power to a separate fuse box in it from your main box, that would be a SUB-Panel, and the electrician would BREAK the bonding strip between the neutral and ground in it.  If he didn't, you MIGHT have those nasty ground loop problems.  The third wire between the main and sub panel gives you your electrical connection back the the bond in the main box.

On our RVs, the main fuse box at the campground has it's neutral and ground bonded, and the fuse boxes in our RVs is considered a sub-panel of that, so again, it's not bonded.  With a built in genny, the transfer switch takes care of the bonding  when it switches over.

Free standing gennies can go either way.  If they expect you to use it to power your house during a power outage, it's usually not bonded, because the fuse box is, and as I said, there can be only one.

Hope that clears it up a little for you.
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SeilerBird

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Re: Grounding a portable generator
« Reply #4 on: September 01, 2018, 04:48:13 AM »
Hi I new to rving and have recently purchased a new 17ft travel trailer. I also just purchased a 4000w portable generator. My question is if I need to ground it or not. The manual states to ground it so the GFIs work properly. Ive talked to some friends and they said they never have grounded their generator. Ive been searching the web and have noticed this is kinda a back and forth subject to ground or not to ground. Any thoughts would be helpful. Thanks
Wow, that is amazing. The manual states to ground it so the GFIs work properly? Ground has absolutely nothing to do with the operation of a GFI. A GFI measures the amperage of the neutral and the amperage of the hot wires. If they are identical then it allows the current to keep on moving. If there is a leak and therefore a mismatch of around 5 milliamps then it trips the circuit in less than 1/30th of a second. That leaked current is going to ground, but there is no ground wire in the circuit. The leaked current is going to ground either through an alternate path, such as water or a human being. The beauty of a GFI is the speed at which it detects the ground fault and trips the breaker. The fellow who invented the GFI gave a public demonstration to prove the worth of the GFI by holding a radio that was plugged into a GFI outlet and jumped into a bathtub full of water. He lived and every new building constructed since then is protected by GFIs.
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blw2

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Re: Grounding a portable generator
« Reply #5 on: September 01, 2018, 05:40:49 AM »
piggybacking StevieG's thread here I know, but I'm hoping questions will help the OP too....

So then why does my little portable construction generator have a ground lug?
I'm guessing that since StevieG's manual states to ground it, that it would also have a ground lug too.

I understand the concept of breaking the bond at a sub panel, but if I look at this in my very mechanical mind, it doesn't seem to be the same here.  Ditto with the idea of not needing to ground it perhaps, if it's feeding into a house's panel.   

In this circuit though, we have no actual path to ground.  We have the power plant (my little portable construction genny) and an extension cord feeding my refrigerator which is standing on a non-conducting tile floor.  I see the floating ground.... essential the neutral which would be the negative side of the wave coming form the actual generator...but I'm not understanding where the "ground" is.

Same thing in an RV mounted generator.  The whole thing is sitting up on rubber tires. (when not plugged into shore power).  No path to ground at all.....
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SeilerBird

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Re: Grounding a portable generator
« Reply #6 on: September 01, 2018, 05:48:11 AM »
The short answer would be the same reason you don't need to ground your car while it is driving down the road or the need to ground a flashlight. There is no potential voltage between the generator and the ground.
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Optimistic Paranoid

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Re: Grounding a portable generator
« Reply #7 on: September 01, 2018, 06:09:16 AM »
Wow, that is amazing. The manual states to ground it so the GFIs work properly?

Well, keep in mind that many of these manuals are translated from some language other-than-English.

I would have sworn that the manual that came with one of my old Japanese bikes had been translated from Japanese into Turkish, and then somebody else translated it from Turkish into British.  It kept talking about the need to 'de-coke the mufflers' . . .
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StevieG

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Re: Grounding a portable generator
« Reply #8 on: September 01, 2018, 08:31:24 AM »
As blw2 stated that his generator has a ground lug. Mine does too on the front panel near where the GFI plug ins are. Ive tried to post a pic but I have to reduce the size of them first.
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SeilerBird

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Re: Grounding a portable generator
« Reply #9 on: September 01, 2018, 08:34:27 AM »
As blw2 stated that his generator has a ground lug. Mine does too on the front panel near where the GFI plug ins are. Ive tried to post a pic but I have to reduce the size of them first.
Yes it does have a ground lug. But it is still not necessary.
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Gary RV_Wizard

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Re: Grounding a portable generator
« Reply #10 on: September 01, 2018, 08:54:25 AM »
Actually, the NEC & OSHA do recommend adding an earth ground to a portable generator and that's the reason they come with ground lugs.  It isn't required for every use (a concession to being "portable"), but there are conditions where an earth ground (the rod driven deep into soil) is required.  Generally, though, there is no requirement to use a ground rod when powering an RV or other plug-in equipment with a portable generator.  There may, however, be a need for a ground-neutral bond, which is related but different (see subsequent para on bonding).

If you want to get into the dirty details on earth ground requirements, see https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.html


That leaves the question of what does "ground" mean on a potable genset.  It has nothing to do with GFCI (see Seilerbird's reply). The ground wire pin on a portable genset is bonded only to the generator frame.   However, equipment such as a Surge Guard or PI EMS will signal a fault if it cannot detect an ground bond, meaning it cannot sense 120v between the hot & ground pins. The solution to that is the use a ground bonding adapter, which basically is a dogbone-type adapter that has the ground pin jumpered to the neutral pin.  This creates the same "neutral ground bond" that is normally present in the load center (breaker box) in your home or business and any equipment that expects ground bonding will work fine with it.  They are easy to make, though I don't know of any source to buy one.

Learn about ground-neutral bonding plugs for portable gensets at http://noshockzone.org/generator-ground-neutral-bonding/
« Last Edit: September 01, 2018, 09:42:36 AM by Gary RV_Wizard »
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Re: Grounding a portable generator
« Reply #11 on: September 01, 2018, 09:00:06 AM »
If you want to get into the dirty details on earth ground requirements, see https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.html

Fixed the link for you
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Optimistic Paranoid

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Re: Grounding a portable generator
« Reply #12 on: September 01, 2018, 09:02:39 AM »
Rule #1 for Boondockers: DON'T FEED THE VULTURES!
My Body is a Temple!  Ancient, Crumbling, Probably Cursed...
I don't like to make advanced plans.  They cause the word "PREMEDITATED" to get used in court!

Optimistic Paranoid

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Re: Grounding a portable generator
« Reply #13 on: September 01, 2018, 09:06:29 AM »
Looks to me like the grounding lug is there so you can attach it to the already existing ground rod of your house, if you are powering your house via a transfer switch.

Certainly nobody expects someone to drive a ground rod into the dirt at every campground.
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StevieG

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Re: Grounding a portable generator
« Reply #14 on: September 01, 2018, 09:26:05 AM »
I figured out how to resize and upload the pics. As you can see the grounding lug on the front panel.
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Gary RV_Wizard

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Re: Grounding a portable generator
« Reply #15 on: September 01, 2018, 09:47:01 AM »
I fixed the typo in my original link to the OSHA site.

Yes, the ground lug is there for use when required, e.g. powering a house or building.  It's never wrong to connect a ground rod and I might do that if using the genset regularly over several day period, but it's not needed for every use.
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StevieG

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Re: Grounding a portable generator
« Reply #16 on: September 01, 2018, 10:27:06 AM »
Thanks for all the reply's. I did watch that video and will be purchasing a bonding plug. I will also test my generator to see if it reports a open ground. Everyone's info has helped. Thanks.

PS - I will probably be asking about winterizing my travel trailer in the near future since we live in MN and don't want any busted or frozen lines.   
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xrated

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Re: Grounding a portable generator
« Reply #17 on: September 01, 2018, 05:33:22 PM »
Campground Manager:  Yes sir, may I help you today?
Camper guy:  Uuh, yea.....I was driving my ground rod at my campsite, and I think I may have hit a water line!
Campground Manager:  Why do you think that you may have hit a water line?
Camper guy:  Cause there are about 20 kids in swimsuits running through the geyser next to my trailer!

Driving a ground rod in a campground would probably be a really bad thing to do! 
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SeilerBird

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Re: Grounding a portable generator
« Reply #18 on: September 01, 2018, 06:07:30 PM »
Driving a ground rod into a water line would be a walk in the park compared to driving it into an electrical line. :o
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John From Detroit

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Re: Grounding a portable generator
« Reply #19 on: September 02, 2018, 08:25:40 AM »
Ok the purpose of a GFCI is to protect you should YOU become a return path for power.
IF you GROUND the generator. and bond Neutral to Ground then YOU can become a return path

IF the gernerator is not grounded or bonded YOu can NOT become a return path so you are protected.

THe GFCI's will work properly if it is BONDED. Grounding makes no difference.  to them since nothing in the generator is grounded.

on MAINS power it makes a difference.
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Re: Grounding a portable generator
« Reply #20 on: September 02, 2018, 09:34:45 AM »
Quote
IF the gernerator is not grounded or bonded YOu can NOT become a return path so you are protected.
So, if I stand on the earth next to my RV in bare feet and grab a hold of a black wire in an outlet box, I can't get electrocuted?  :o
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Jim18655

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Re: Grounding a portable generator
« Reply #21 on: September 02, 2018, 10:57:23 PM »
In theory - no shock. The power from the alternator unit should be isolated much like a battery. Alternators, like transformers, need a neutral/ground bond to create a safety ground and either leg can be grounded. Strangest power system I every worked with was 440 corner grounded delta. A live leg is connected to ground. If the genset frame isn't sitting on bare ground probably no shock. I'll try it tomorrow with a meter.
« Last Edit: September 02, 2018, 10:59:59 PM by Jim18655 »

glen54737

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Re: Grounding a portable generator
« Reply #22 on: September 03, 2018, 04:16:17 AM »
Gary you will get a shock. It's difficult to determine the voltage.
You really don't want to bond a current carry conductor to ground if you do you should ground the chassis of the portable generator too.
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Gary RV_Wizard

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Re: Grounding a portable generator
« Reply #23 on: September 03, 2018, 10:08:43 AM »
The recommendation at noshockzone.com is to bond neutral to ground at the genset, essentially creating the same situation as exists in an onboard genset.  The ground wires in the RV always include a chassis ground (chassis bonded to load center ground lug), but the RV system has no path to ground unless provided by the power source.


My query above was facetious; there is always some possibility of shock.  GFCIs and ground wires will eliminate many common causes, but are never 100% foolproof.
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Lou Schneider

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Re: Grounding a portable generator
« Reply #24 on: September 03, 2018, 10:55:05 AM »
A generator sitting on rubber feet, or with rubber isolation bushings between the motor/generator and the frame, or with internal isolation so both hot and neutral are isolared from the frame is an isolated power source.  There's no connection to earth ground, so in theory there's no possibility of shock if you come between one of the voltage conductors and ground.

Isolated power is used all the time in operating rooms for just that reason.  There's a low leakage isolation transformer creating the isolated power so a patient on the operating table won't receive a shock from stray currents on the medical devices.  An isolated ground outlet will have a small triangle next to the ground pin, indicating the ground wiring is independent of the power source.

So yes, in theory Gary could grab one of the live wires while standing barefoot in a puddle and not get a shock ... as long as the generator isolation remains perfectly intact.

In practice, there are many ways to degrade that perfect isolation, including capacitive coupling of the generator to the ground it's sitting on.   So in practical terms, be aware there's a possibility of getting a tingle from an isolated generator if multiple things go wrong at once.
« Last Edit: September 03, 2018, 11:03:51 AM by Lou Schneider »

Gary RV_Wizard

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Re: Grounding a portable generator
« Reply #25 on: September 03, 2018, 11:10:30 AM »
I think the theory falls short of practice when dealing with the planet Earth.  It's such a massive ground sink, connected to so many power generation sources,  that some current will flow regardless of the local isolated source. The voltage may not be identical to the local, but it's probably not going to be zero either.

Would be interesting to survey some typical RV situations using unbonded generators (e.g the Honda and Yamaha inverter generators). Just use a voltmeter from a hot wire in the RV or the genset itself to physical earth (just stick the probe in the ground) and see what you get.
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Jim18655

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Re: Grounding a portable generator
« Reply #26 on: September 03, 2018, 06:49:12 PM »
Took some volt readings today.
With the generator metal foot sitting on the damp ground I read 120 volts to my service ground rod about 3' away.
With the metal foot on a rubber welcome mat  on the concrete sidewalk I got 30 volts to the ground rod 3' away.
I didn't isolate the tires from the dirt and I don't know how conductive they might be since carbon black is used to color plastic.

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Re: Grounding a portable generator
« Reply #27 on: September 03, 2018, 08:32:10 PM »
What kind of current readings do you get? Start with the highest ampere range and work downwards.  I'll bet there isn't more than a few milli- or microamps.

HueyPilotVN

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Re: Grounding a portable generator
« Reply #28 on: September 03, 2018, 11:53:56 PM »
When deploying any of our mobile surgical facilities with dual 150KW generators the first thing that we do is to drive a 6 foot copper grounding rod into the earth as a safety factor.
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Re: Grounding a portable generator
« Reply #29 on: September 04, 2018, 05:42:15 AM »
For all practical purposes, if one needs to ground the generator frame, a decent metal tent peg would be sufficient. You shouldn't have to drive a 100' x 5/8" ground rod. Running a wire from the grounding lug on the frame to the water riser with a sizeable alligator clip will be plenty.
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