Portable Generators and Ground Rods

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Re: Portable Generators and Ground Rods

Originally posted by hickman:An accident severs the grounded conductor of the service entrance conductors leaving the ungrounded conductors intact. You in your haste never installed a ground rod to the frame. You go over to the genset and grab the frame of the generator. What do you think will happen?
I think nothing will happen, unless you accidentally cut your hand on a sharp edge of the frame. Your description of the ?accident? did not include a fault between an ungrounded conductor and the grounded conductor, or between an ungrounded conductor and any grounded external metal components. Therefore, no current will flow into planet Earth, and none will flow through the human who touches the frame.

As for myself I do not care to be the path of any electrical current, Nor will I allow my clients. So I drive the ground rods.... I believe in grounding. even if it is poor at times it is better than nothing. And I would hope that you would feel the same.
I think it?s safe to say that no member of this forum is in favor of electrocuting our clients. As for me (and I think I?m not alone here), I believe in (1) Following the code, (2) Following the manufacturer?s recommendations, (3) Following ?good engineering practice,? and (4) ?Throwing a flag on the play,? if ever items (1) through (3) were to conflict (i.e., stop the job, notify the key personnel, and proceed no further until the issue is resolved).
 
Re: Portable Generators and Ground Rods

Charlie,
a ground rod does not serve the function of providing personnel protection for anything short of medium voltage systems.
"unless there is a device to detect ground faults." There are millions of homes outside North America that relies soley on a ground rod.

awwt,
It is possible to protect the whole building with a single gfci. It is the standard setup where I live to use a single gfci for single family homes, with some 'crucial' circuits like the freezer outside this protection. To put the freezer and heating system on the gfci could be very dangerous for the electrican, should it trip when the homeowner is not at home. ;)

I persuaded my parents to install one a few years ago. It has tripped only twice. Once when a cord caught fire and once when my grandmother put a knife in the toaster. Note that I'm not in North America.
 
Re: Portable Generators and Ground Rods

Originally posted by pierre:
Bob
If I may answer the three scenarios you have stated? This is my interpretation of 250.34.
All three of the situations would require a ground rod.
They do not meet the requirements of 250.34(A)(1).
I am guessing (I am not using the ^$$uming word) that this equipment you are discribing is not cord and plug connected, but is hardwired.

Pierre
No, all this equipment was cord and plug connected so it is my belief that no ground rod is mandated.

But I also believe that Bennie is very knowledgeable and if he tells me a large generator develops a static charge I have no doubt that is true, so this leaves me with the NEC not requiring a ground rod when they may be a need for one.

Thanks for you thoughts on this, Bob :)
 
Re: Portable Generators and Ground Rods

Hickman, I hope you will stick around even if you are finding a difference of opinion here.

I started this thread and the others have responded because we are all concerned with protecting people from electric shock.

The people that are responding are very knowledgeable electricians and engineers.

When all these people disagree with my position, I have to reconsider my beliefs, I suggest you do the same.

Please take the time to draw the fault you describe above and try to follow the path of the fault current.

It seems you really care about doing your job safely, but I think you are mistaken on what a ground rod can do for us.

Glad to have you participating, but please try to keep an open mind here.

Bob
 
Re: Portable Generators and Ground Rods

Look at this as a 120 volt bank of batteries. Do you see any reason to drive a ground rod?

Any metal around the batteries should be grounded for electrostatic equalizing. This would require a ground electrode of some type.

The power system does not have to be grounded, but it is permitted.
 
Re: Portable Generators and Ground Rods

How does 250.30 (A)(2) play into this? I am speaking about a built-in generator. I know that portable generators are exempt from 250.30 (A) (2) but it appears this thread is also talking about built-in generators (permanently installed).

../Wayne

Post edited to clarify that I am talking about permanent generators only.

[ September 07, 2003, 05:47 PM: Message edited by: awwt ]
 
Re: Portable Generators and Ground Rods

250.30 concerns premises wiring systems not portable generators.
 
Re: Portable Generators and Ground Rods

Hickman
If you want to do a experiment to show how little a ground rod will not protect a person, Just drive a 10' ground rod into the ground then take a hot from a 15 amp breaker and connect it to it and turn it on of course have a switch in-line close by so no one can sneak up and touch it without you there but this ground rod will now be at 120 volt potential to earth and there will be a step potential expanding out from this rod. Put a amp-Prob on the hot feeding this rod and you will be shocked (no pun intended) as to how little the current will be. the problem is the resistance of a ground rod does not allow it to safely bring the voltage down to a safe level and this is a very BIG FALSE SENSE OF SECURITY! This is one of the biggest misunderstood beliefs that many believe is true and has killed many people. From installing a ground rod at a light pole standard to using a ground rod to protect a Mobile home with the separation of the grounds and neutrals. look at it this way.
(And this is a true story)
I had an elderly Friend that lived in a trailer park. The state was making the parks upgrade the hookups as many were unsafe.
This park where she lived hired a contractor from out of state to do the work which required the removal of the uninsulated grounding conductor and install a new insulated one.
This contractor talked the state HUD inspector into allowing him to just install two ground rods one at the trailer and one at the service pack. but the inspector told him that the neutral and grounding conductors must not be bonded at the trailer as said in the NEC.
Now what happened was she came home one night and went to put her key into the lock on her door. (ALL is bonded to the metal frame which is bonded to the ground rod at the trailer) she was electrocuted and sent her to the hospital(luckily her neighbor was watching) She was hurt and never recovered totally, she passed away last year about a year after this happened.
I did an investigation to what had happened and found that the electric dryer heating element had shorted to the frame of the dryer which was bonded to the grounding buss in the panel then this was only connected to the ground rod but because of the high impedance between this rod and the one at the service it did not open the breaker in-which brought the whole grounding system on this trailer up to 120 volts potential to earth. the fault path of bonding was broken by not having a solid grounding wire ran to the service equipment and bonded to the neutral at the service equipment. I did bring it to the attention of this inspector which at the time we didn't know how hurt she was, but it did scare him enough to require the out of state contractor to come back and rerun all the grounds.

This is why the effect of a ground rod will have no effect on safety as the resistance will limit the amount of current the rod can fault and this would only cause the ground rod (and any thing else connected to it) to go to 120 volt potential to earth without tripping a breaker and without the tripping of a breaker THERE IS NO PROTECTION TO PERSON'S WHO MAY COME INTO CONTACT WITH THIS GROUNDING SYSTEM!!!!

Installing a rod for a generator will only provide a path for a person to get in between the source and return. without the rod this cannot happen period!!!

120 volts divided by 25 ohm's only allows for 4.8 amps to flow and 4.8 amps will not open any breaker save a GFCI like I said before with out the opening of a breaker the grounding of a system will go to a 120 volt potential and can injure anyone comming into contact with it.

[ September 05, 2003, 08:09 PM: Message edited by: hurk27 ]
 
Re: Portable Generators and Ground Rods

Bob iwire, I have been following this thread for some time now, and chosen to stay out until now. I am sure you know the 5 reasons for connection to earth.

1. Planned discharge path for lightning.
2. Accidental contact with HV or MV
3. Stabilize system voltage.
4. Minimize touch potential.
5. Static discharge path.

Cannot remember what the portable generator was being used for, seems like a outdoor sound stage, carnival rides, or construction power tools.

In any event the only plausible reason I can come up with is 4 or 5. Take your pick. Not certain a ground rod is even required, depends on the application.

Mr. Hickman, I share the same point of view as Bob Iwire, you seemed concerned for personnal safety, but your preception of what a earth connection is for if is flawed. By code earth cannot be used as a fault path for the reasons many have stated. If I were power god, I would eliminate grounded systems altogether, they are dangerous, designed to fail, and antiquated.

[ September 05, 2003, 08:18 PM: Message edited by: dereckbc ]
 
Re: Portable Generators and Ground Rods

Here is something else to think about!
There is things that we all must think about when we take on a job.
1. Do we have the true knowledge to do this job safety
2. We can be responsible for those who we injure.
3. We can be held criminally liable for those we injure or kill (this was posted a few months ago that an electrician got 5 years for involuntary manslaughter)
4. We will have to live with ourself when this happens and it can be very destructive ot ourself if we knowingly harm or kill someone.(even worse a child)
5. Never say I know already. as this is a sign of someone with a closed mind. A person with a closed mind will not learn anything new because he thinks he already knows it, and it cant be done any better. This is why we must always KEEP AN OPEN MIND to everything as there is always something new to learn and a different way to understand a problem.

Always Keep your mind open to new understanding, even if you have done it this way for a thousand years. it could be still wrong and would you bet someones life one that?
 
Re: Portable Generators and Ground Rods

Bob,Dereck, and Wayne (Hurk) excellent posts.

Roger
 
Re: Portable Generators and Ground Rods

Sorry I could not stay to respond. Had to do that work thing. Has any of you read article 90 of the nec. I feel that I am being attacked for following the code. Charlie why do you think that no current will flow if the neutral is cut before the service disconnect? In my mothers house a few years ago the neutral corroded through. The resulting 220 circuit burned every 120 volt appliance in the house.However some of the circuits that I put my meter on still read 120 volts. Where did that electricty go if not out the ground rod. Line man still put copper plates on the bottom of power poles and bond then to the grounded conductor and they still bond at the transformers. Why? Is it because they have nothing better to do? Or is it to give stray current a safe path back to the source. As for the lady at the trailer park. The IAEI publishes most accidents and their cause. If she was seriously injured I am sure they will have a listing for her in there some where and the findings of their investigation. As for my hypotheitical accident. You should still have a grounding electrode at the first point of disconnect. What is an Electrode. Webster defines it as a conductor used to establish electrical contact with a nonmetallic part of a CIRCUIT. What circuit? I think that if you are so against ground rods at the generator. Submit a change to the code making panel. If they change it Great. At that point I am on your side. Until then I stick to the code. Personally I don't like ground rod's. I would rather see it bonded to the service. Ufer grounds and water pipes are better than ground rods. However I stick to my statement that a ground rod, as poor as it is, is still better than nothing at all.
 
Re: Portable Generators and Ground Rods

Originally posted by bennie:
250.30 concerns premises wiring systems not portable generators.
Right I know that. I have edited my post to reflect that.

../Wayne

[ September 07, 2003, 05:48 PM: Message edited by: awwt ]
 
Re: Portable Generators and Ground Rods

What makes you think that I am not talking about a portable generator. Try a Guardian Model 4582 with model 4397 transfer switch.
 
Re: Portable Generators and Ground Rods

Sorry I have to aploligize, But you guys are so hard headed that you are making me angry. :mad:
 
Re: Portable Generators and Ground Rods

I do have a question though, for all of you engineers who seem to be so well versed in lightning. I have noticed that tree's that have been hit by lightning here in Utah Have a chunk of wood blown off the tree about 2 inches wide and about 1 inch deep that spirals counter clockwise about 1 full rotation per about 100 feet. Any one know why?
 
Re: Portable Generators and Ground Rods

Hickman, I'm sorry but what you are arguing you don't understand. You are doing by the old "I've always done it that way so it must be right" standard.

Example
What happened in your mothers house never put leg to leg voltage (220, 230, or 240v) across any device that burned up. It was as simple as basic ohms law. Take the resistance of the devices being in series between two legs of a multi wire circuit and the voltage drop across each of these resistors. One may have seen 170v and the other 50v until one acted as a fuse and openned the series, but if both circuits were equal the devices would have kept on working with no problems.

You could have read 120v with very little reference if there was no load applied.

I know this is drifting from the ground rod issue but still poses questions as to where your coming from.

Don't get mad, forget what we are saying and open your books, you referenced Mike Holt literature earlier and have been shown a diagram from Mike Holt and also instructed by another member to go back and read the literature you mentioned. So if it takes it, forget us and study for your own safety.

Roger

[ September 05, 2003, 10:40 PM: Message edited by: roger ]
 
Re: Portable Generators and Ground Rods

Roger, Hurk back on page 6 told me to drive a ground rod into the ground and connect a 15 amp circuit breaker to it. Lets say that I do. The worms will start crawling out of the ground. And you will get shocked. Now I ask current is flowing, but to where? And how is it getting there. Manufactures recomendations are that you do not bond the neutral to the grounding electrode in their generator, but instead do it at the first point of disconnect. Pretty standard. However They want a ground rod. Why? They bond the neutral to the frame in the generator. I have seen it. Why? Can't blame it all on lightning Because you have the same requirements when installed indoors.
 
Re: Portable Generators and Ground Rods

hickman,
Hurk back on page 6 told me to drive a ground rod into the ground and connect a 15 amp circuit breaker to it. Lets say that I do. The worms will start crawling out of the ground. And you will get shocked. Now I ask current is flowing, but to where?
And what would happen if the power source for the 15 amp circuit was an ungrounded source?
Don
 
Re: Portable Generators and Ground Rods

Hickman:
Manufactures recomendations are that you do not bond the neutral to the grounding electrode in their generator, but instead do it at the first point of disconnect . Pretty standard. However They want a ground rod.
The ground rod that the manufacture is requiring and the one that the NEC requirs is one in the same.
There is no requirment to add another rod unless you don't meat the 25 ohm's with the first one.
All this manufacture is covering for the many houses that were built when ground rod's were not required. If there's a rod already installed then the connection of the generator to the service or panel will bond it to this rod.
As far as the ground rod protection from a loss neutral give it up as I have had many houses that have loss there neutral and the ones that didn't have a water pipe ground with city water. they still lost appliances as again a ground rod with a resistance of 25 ohms will only pass 4.8 amps this means that for it to protect this house the neutral current would have to stay below 4.8 amps or it will start to go unbalanced. And the reasone the houses with a water pipe bond didn't have this problem is the water pipe is bonded at the next houst which is bonded to the neutral at the next service. Again the ground rod serves no great purpose for falt current and will not prevent touch potential by it's self as the earth resistance is to high.

Even the NEC reconizes this as this is why they have artical 250.4 (D)
as said in this statement: "The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path ."
Now if you cannot remove the touch voltage off the grounding with a ground rod then how does it protect from shock? this is why a breaker must blow before the shock hazared is removed. And at 4.8 amps there is not any breakers in a home panel that a ground rod would trip.

250.4
(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path.

(1) Grounding Electrical Equipment. Non?current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials
 
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