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ground rods and portable generators

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grandpapastu

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I was aptly corrected of my old school and technically incorrect statement when I said that electricity takes the path of least resistance to ground. Actually electric current seeks the path of least resistance to source.

So in the case of a portable generator that does not have the windings at any point bonded to the frame and grounding lugs, how could a ground fault current seek to flow back to source, even if a ground rod was driven and bonded to the frame of the generator?
If no circuit exists for the ground fault current flow then what would be the use of portable generator GFCI protected receptacles.
 
Re: ground rods and portable generators

Originally posted by grandpapastu:
Actually electric current seeks the path of least resistance to source.
Click to expand...
Correction again, current takes all paths availible back to the source.

The portable generator grounded circuit conductor you described is required to be bonded to the frame, but the frame is not required to be earthed.
 
Re: ground rods and portable generators

Originally posted by grandpapastu:
Actually electric current seeks the path of least resistance to source.
Click to expand...
Actually, current seeks all paths back to the source. The path of least resistance is hopefully your effective ground-fault path, all the rest are just ground-fault paths.

So in the case of a portable generator that does not have the windings at any point bonded to the frame and grounding lugs, how could a ground fault current seek to flow back to source, even if a ground rod was driven and bonded to the frame of the generator?
Click to expand...
This is usually done by the manufacturer. Why wouldn't there be this bond? :confused:
 
Re: ground rods and portable generators

Bryan,
This is usually done by the manufacturer. Why wouldn't there be this bond?
Click to expand...
It is my understanding that this bond does not exist in many small portable generators.
Don
 
Re: ground rods and portable generators

Are the generator manufacturers in the USA required to attach a label indicating whether the winding center tap is bonded to the frame or not?

That is now a requirement in Canada.

Ed
 
Re: ground rods and portable generators

A friend of mine was using a portable generator with a three-prong extension cord to power a few small items (e.g., coffee pot) at a camping site. Just for the amusement, I plugged my home-owner?s style 3-light (yellow, yellow, red) circuit tester into the extension cord, and then into the receptacle on the generator itself. In both cases, only the center yellow light was illuminated, which means ?open ground.? Now I know that the generator?s neutral and frame are supposed to be bonded, and that this point does not need to be ?earthed,? but I do not know how the circuit tester does its thing.

Was this the correct reading for a properly connected generator? Does the circuit tester require a path to planet Earth, in order to show a proper connection (i.e., two yellow lights illuminated)? Or should I advise my friend to have his generator checked out by a repair shop?
 
Re: ground rods and portable generators

dereckbc Sir,
Seems like I read once on this forum that some small portable generators may not have the grounded circuit conductor bonded to the frame; and if that were the case then it would make me question some things.
I won't develop any hypothetical construct here but it just had me thinking. I would expect the frame of the generator to be bonded to it's neutral and that clears it up for me.
Thanks.

Electric current does seek the path of least resistance back to it's source. I did not say that it seeks the path of least resistance only back to it's source.
Of course current will develop across all paths available to it. This is a fact that my statement does not disagree with fellas. The intent of the statement is only to draw attention to one characteristic of electric current pertinent to an example I posted earlier (not this topic) of a corroded/damaged (high impedence, nearly open) underground service lateral grounded service conductor at a residence that was the cause of a fire.
And in that example a parallel return path to source developed. One conductor in the parallel circuit was a 12 AWG equipment grounding conductor which actually started the fire.
If the grounding electrode system had been correctly designed and installed before the fire, then the grounding electrode conductors would have provided the path of least resistance to ground (opps! I mean source) even though that is not there intended purpose, little or almost no current would have developed across the 12 AWG equipment grounding conductor, and probably no fire started.
If the grounded service conductor had of been in good shape then of course it would have continued to provide the path of least resistance to source and no significant amount of current at all would have developed across the other conductors in the circuit.
Thank you gentlemen for your most valued input.

[ May 27, 2004, 10:55 AM: Message edited by: grandpapastu ]
 
Re: ground rods and portable generators

CharlieB Sir,
I am pretty sure that the tester would only read 'correct' if the generator's grounded conductor was bonded to the generator frame and to the equipment grounding conductor terminal of the generator receptacle.
Earth grounding the frame of the generator would not provide a source return path or closed circuit for to enable the tester to read 'correct'.
The electric potential of the earth is assumed to be zero. When a metal object such as the frame of the portable generator your using is connected to the earth by means of a ground rod for example then it too thereby is forced to take the same zero potential as the earth and in the case of your generator this would be the only thing accomplished by grounding the generator frame to earth.
dereckbc, commenting earlier, said that the grounded circuit conductor of the portable generator is required to be bonded to the generator frame; so, taking that into consideration I would have the thing checked out by the repair shop if I were you.
There is no need to design and create any additional ground return paths by driving a ground rod though and for personal safety I would want the generator receptacles to be GFCI protected.
 
Re: ground rods and portable generators

grandpapastu
If the grounding electrode system had been correctly designed and installed before the fire, then the grounding electrode conductors would have provided the path of least resistance to ground (opps! I mean source) even though that is not there intended purpose, little or almost no current would have developed across the 12 AWG equipment grounding conductor, and probably no fire started.
Click to expand...
Unless the grounding electrode system is a common underground water piping system that is connected to the utility source at other locations, it is very likely that the #12 EGC will still be the path of least resistance by far and will still carry most of the current.
Don
 
Re: ground rods and portable generators

don_resqcapt19,
are you talking about if the grounding electrode system had been installed correctly prior to the fire?
Then, oh yeah, sure the grounding electrode system would have included an underground water pipe system bonded by means of a GEC to the service point.
In the case I cited the underground metal water pipes were not bonded by GEC to the service point prior to my reconstruction of the system. The only grounding electrode used was a single ground rod.
The 12 AWG equipment grounding conductor connected the neutral/ground bar of the MBO loadcenter to the frame of the dishwasher which in turn was connected to the metal underground water pipe system. The system operating current thus returned through 12 AWG, through the water pipe and earth ground to source (transformer pad)in a parallel circuit with the existing ground rod and the nearly broken grounded service conductor.

Now with a grounding electrode system correctly installed prior to the fire, by far the greatest value of the system operating current would have sought the grounded service entrance conductor of the SER cable from the MBO panel back to the service point and through the GEC to water pipe through earth ground to source.
The 12 AWG connected to the frame of the dishwasher and the newly driven ground rods would have still yet provided parallel paths back to source along with the water pipe, but, of such negligible values relative to the path just outlined that no fire would have resulted.

[ May 27, 2004, 04:27 PM: Message edited by: grandpapastu ]
 
Re: ground rods and portable generators

So what are you getting at?

The system you describe was not code compliant, a fire resulting is not a surprise.
 
Re: ground rods and portable generators

Gettin' at? Getting at as get can, man.
Check out the context.
No surprises here. Not code compliant? Really?
No kidding!
This is atleast an interesting case scenario I'm interested in layin' on you man so that I may even solicite your most valued input Sir.
Many points of interest that may be developed from this actual case history involving an emergency service call assigned to me a couple of years ago down in Peachtree City, GA.

I believe the original context was a demonstration of the current seeking the path of least resistance to source in a parallel circuit and the efficacy of ground rods.
I mean, using atleast a couple of ground rods and spaceing them atleast 8' apart, doing the best you can to obtain an earth ground resistance of 25 ohms or less with them, would have helped some to reduce the current across that 12 guage grounding conductor.

Also it just goes to show an interesting situation wherein a properly designed and installed grounding electrode system could have prevented some property damage and reduced the potential developing for danger to persons.

[ May 27, 2004, 04:17 PM: Message edited by: grandpapastu ]
 
Re: ground rods and portable generators

Originally posted by charlie b:


Was this the correct reading for a properly connected generator? Does the circuit tester require a path to planet Earth, in order to show a proper connection ? Or should I advise my friend to have his generator checked out by a repair shop?
Click to expand...
No, No, Yes.
 
Re: ground rods and portable generators

grandpapastu,
My point is that if the is no metal underground water piping system, it is highly unlikely that the code compliant grounding electrode system would have made any difference in the case you are talking about. The impedance of most code compliant grounding electrodes, other than a common metal under ground water piping system, is too high to permit much current flow.
Don
 
Re: ground rods and portable generators

don_resqcapt,

quote:
__________________________________________________

My point is that if there is no metal underground water piping system, it is highly unlikely that the code compliant grounding electrode system would have made any difference in the case you are talking about.
__________________________________________________

Yes I agree with you.
Such a hypothetical construct does not however negate the efficacy of correctly installed ground rod(s).
I was suggesting, in context with the case that I was talking about (which did in fact have the metal underground water pipe system available) that, using at least a couple of ground rods and spacing them at least 8' apart, doing the best you can to obtain an earth ground resistance of 25 ohms or less with them, would have helped some (underline) to reduce (underline) the current across that 12 AWG equipment grounding conductor in that parallel circuit. A desirable difference will always be realized by a correctly installed and code compliant system.
With no metal underground water piping system available, then of course no return path could there be by means of that 12 AWG EGC bonded to the dishwasher frame and it could not have started the fire anyway.
grandpapastu.

don_resqcapt

quote:
__________________________________________________
The impedance of most code compliant grounding electrodes, other than a common metal under ground water piping system, is too high to permit much current flow.
Don __________________________________________________


O.K., yep, exactly and I agree.
In the case I cited however there was a metal underground water piping system that was tied in with the reconstructed grounding electrode system and if such a system as that had been in place along with code compliant (25 ohms or less resistance to ground) ground rod(s) installed prior to the trouble with the underground service lateral neutral then the current realized across the 12 AWG EGC would have been limited to a negligible value and such value would have been reduced due at least in some part by the code compliant ground rod(s) installed. Any reduction in the value of the current realized across the 12 AWG EGC would have been desirable.
grandpapastu.

[ June 04, 2004, 11:42 AM: Message edited by: grandpapastu ]
 
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