Grounding a portable generator

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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?  :eek:
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
HueyPilotVN said:
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.

Grounding is required... if I recall correctly (Please do not take my word for the number) on Generators over 50KW.. but as I stress I may be off on the KW
 
I used a portable generator in a sailboat.  Never grounded it.  never had a problem.  Grounding in a sailboat usually means running a heavy wire and attaching it to the metal keel bolts.
 
Actually the big thing to avoid is something you have not mentioned. That is the neutral-ground bond. In a typical AC system, there is a "bond" between the white neutral wire and the bare(or green) ground wire made in the AC load distribution center. There should only be one bond in the system. The problem comes in when a generator is introduced. There is no industry-wide standard whether or not the generator shall or shall not have the generator neutral and ground wires bonded within the generator.

You should examine the wiring schematics for each piece of equipment to ascertain if they have an internal neutral-ground bond.

Often portable generators (Mod note: affiliate link removed) with chassis-mounted receptacles have internal bonds. It's best to have the neutral-ground bond at the main AC panel, so bonds in equipment must be removed.

The same neutral-ground problem can arise with an inverter; some bond and some do not.

Grounding is best accomplished by driving an 8 ft copper-clad rod into the ground and connecting that to a ground block or bus using a single #6 copper wire. Then each piece of equipment is connected to that ground block. This would include a charge controller if/when PV modules are introduced to the system. There is nothing wrong with having a second ground rod in the system. If there is a second ground rod it should be connected to the first ground rod with #6 wire. The second rod should not connect to the ground block/bus or to any other piece of equipment. A second ground rod is actually required if you wanted to check the efficacy of the grounding system. With two rods there should be a minimum ten-foot separation.

The DC side of the system should also have a neutral-ground bond and there should be a ground rod as well. The NEC does not require a ground rod in a 12 VDC system, but it is a good idea nevertheless.

Is that grey box between the generator and the inverter/charger a transfer switch? Or does the inverter have an internal transfer switch? If the inverter/charger does not have an internal transfer switch there should be a transfer switch. The generator connects to one input side. The inverter/charger AC output connects to the other input side. The transfer switch output then connects to the AC load/distribution center. That way only one source of AC can be feeding the cabin AC system at a time. No danger of mix-ups.
 
Optimistic Paranoid said:
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

Also, here's a link to a lower cost grounding bond plug on Amazon: https://smile.amazon.com/Southwire-Company-LLC-44400-Generator/dp/B07F4R7BDL/ref=sr_1_fkmr1_1?keywords=generator+ground+bonding+adapter&qid=1571362444&sr=8-1-fkmr1

Reviewers say it works fine on RVs.

P.S. Love your irony "Optimistic Paranoid"  ;D ;D ;D ::)
 
SeilerBird said:
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.

Ground has everything to do with a GFI but I'm not going to get into it here. It's described pretty good already in the thread by Gary RV_ Wizard if you care to read about it.  Retired 50 year Master electrician.
 
cavie said:
Ground has everything to do with a GFI but I'm not going to get into it here. It's described pretty good already in the thread by Gary RV_ Wizard if you care to read about it.  Retired 50 year Master electrician.
How did you ever become a 'master' electrician? Gary did not describe any need for a ground for a GFI. Here is what he said:

That leaves the question of what does "ground" mean on a portable 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.
A ground wire has absolutely nothing to do with a GFI. It is totally unnecessary. They work just fine without one. The proof of that is in any RV that is off the grid running on an inverter or a generator the GFI works just fine and there is no ground anywhere. If the ground was necessary then the GFI would not work. The reason you are not going to get into it here is because you can't. I am a retired 52 year UNION electrician. In the union you actually have to go through an apprenticeship and learn how electricity actually works.
 
SeilerBird said:
How did you ever become a 'master' electrician? Gary did not describe any need for a ground for a GFI. Here is what he said:
A ground wire has absolutely nothing to do with a GFI. It is totally unnecessary. They work just fine without one. The proof of that is in any RV that is off the grid running on an inverter or a generator the GFI works just fine and there is no ground anywhere. If the ground was necessary then the GFI would not work. The reason you are not going to get into it here is because you can't. I am a retired 52 year UNION electrician. In the union you actually have to go through an apprenticeship and learn how electricity actually works.

I am very aware of how a GFI works. I have installed many on two wire systems.

It amazing to me how an Edison plug with the neutral and ground tied together and plunged into a portable generator  will solve RV, GFI, and Generator problems. Many RV's will not work without this if you do some research.

The be a Master Electrician I to have to learn the be an electrician. ( been doing that for 50 years) I also must also take hours long test ( forgot how many. About 6 as I can recall. 35 years ago.) to get a License to own the two business I have.  Have a nice day. :) I'm done here.
 
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