Portable Generators and Ground Rods

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Re: Portable Generators and Ground Rods

Originally posted by hickman:
Try doing that an a federal project or one that requires that you prove that 25 ohm's and see how far your arguments take you. Also what about the Gen sets that we install indoors? Still need a ground rod and I don't see any Lightning strikes on them in the near future. There is also the topic if manufactures recommendations. I have seen small portables with a ground lug. If it is recommended by the manufacture it is as good as code no matter who mounted it on the truck.
I believe that the reason many small generators have ground lugs on the frame is to facilitate bonding them to the frame of any vehicle that they might be mounted on. The presence of the lug does not tell you much about the manufacturers intent.

The only manufacturers instructions that can be enforced by a code official are those included in the laboratory listing or the label that bears the laboratory listing mark.
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Tom
 
Re: Portable Generators and Ground Rods

After all of these postings I still have not detected a consensus on the meaning of the language in 250.34 Portable and Vehicle-Mounted Generators.

"cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator"

I have always thought that if the generator supplied receptacles that were not mounted on the set or vehicle that the rules for grounding derived systems applied.

The question becomes if the generator supplies current to feeders; even if those feeders are cord and plug connected; does it have to be grounded as a derived system.
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Tom
 
Re: Portable Generators and Ground Rods

Karl,

I knew that long winded post would have to yeild something for me. :)

Do you know anything about these installations in the UK? Are touch potentials an issue? Is everything simply bonded together like crazy? What is done about lightning protection?

Thanks.
-John
 
Re: Portable Generators and Ground Rods

John, I believe the rod at the Tformer takes care of touch potential at the building. As for lightning protection at the building, that's a good question. Will put it to the UK guys and see what they say. Though I believe that Dereck has said that some 95% or so of strikes are upstream of the local Tformer.

Karl
 
Re: Portable Generators and Ground Rods

2002 NEC Handbook
Portable describes equipment that is easily carried by personnel from one location to another.
Mobile describes equipment, such as vehicle-mounted generators, that is capable of being moved, on wheels or rollers.
The frame of a portable generator is not required to be connected to earth (ground rod, water pipe, etc.) if the generator has receptacles mounted on the generator panel and the receptacles have equipment grounding terminals bonded to the generator frame.
If we stick with this definition, it would end a lot of confusion! :)
 
Re: Portable Generators and Ground Rods

Originally posted by awwt:
Here are a couple of helpful links. Also, follow the links for the video clips:

702.10 Portable Generator Grounding (A)


702.10 Portable Generator Grounding (B)


../Wayne C.

PS: There is a whole menu of video and summaries here:
Mikeholt.com NEC video clip library
Well, I fallowed the links as suggested and that does not answer my question. Lets talk about a completely mobile set up. It does not matter to me if it is a carnival or an amateur radio field day encampment.

I suspect that we can all agree if we run cords from the outlets on the generator to the individual loads with the load cords connected to cord caps on the extension cords that grounding the generator is not required.

What happens when I use a power tap box with the outlets on the box? Those outlets are not mounted on the generator. Do I now have to ground the generator.

What about when the cord supplies a distribution panel that contains circuit breakers and has outlet boxes mounted in or adjacent to the panel. These receptacles are also not mounted on the generator. Do I now have to ground the generator?
We use the portable power tap type boxes in fire and rescue work. The various public events use cord and plug supplied portable panels. It would be really useful to know the correct way to treat these arrangements.
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Tom
 
Re: Portable Generators and Ground Rods

Tom, I started a thread here and another one at another forum in search of just what you are asking.

My take on the responses is this, No the NEC does not require the use of a ground rod for portable or vehicle mounted generators no matter what the size and any cord and pluged equipment can be used from it.

The definitions of portable that have been posted have been opinions and not from article 100.

Some people feel that these generators need a ground rod "if they are too big to carry" i.e. not portable.

I think the thing that makes me sure that you can have cord and plugged panels and distribution boxes down line from a generator without a ground rod is the use of the word equipment in 250.34 instead of the words utilization equipment.

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be grounded and shall be permitted to serve as the grounding electrode for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The non?current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
Equipment. A general term including material, fittings, devices, appliances, luminaires (fixtures), apparatus, and the like used as a part of, or in connection with, an electrical installation.
Utilization Equipment. Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes.
Also to me if they meant portable or vehicle mounted generators to be less then a certain size for this to apply why did they not simply say generators less then xxxxx watts, KW etc.?

JMO, Bob

[ September 15, 2003, 05:10 PM: Message edited by: iwire ]
 
Re: Portable Generators and Ground Rods

While on the subject of generators I wanted to add one additional thing. We operate three 935 KW generators at 600 volts Delta without a neutral. 480 volt distribution system is fed from a 600/480 delta/delta transformer. Again the voltage is floated( no neutral). We have a ground light indication system to show if we have a ground. If we have a ground fault everything keeps working and we locate the ground and repairs are made. EGC are ran to all equipment. And a ground rod is used at the generator. Max current due to a 600 volt ground is around 4 amps.
 
Re: Portable Generators and Ground Rods

hurk,
McLain's system is an ungrounded system. The current to ground will be very limited for a single ground fault.
Don
 
Re: Portable Generators and Ground Rods

hurk27
I should have explained that it is a ungrounded system. The supply cables act like a capacitor and the current flow from a ground fault is caused by this capacitance.
 
Re: Portable Generators and Ground Rods

Originally posted by iwire:
Tom, I started a thread here and another one at another forum in search of just what you are asking.

My take on the responses is this, No the NEC does not require the use of a ground rod for portable or vehicle mounted generators no matter what the size and any cord and plug equipment can be used from it.

The definitions of portable that have been posted have been opinions and not from article 100.

Some people feel that these generators need a ground rod "if they are too big to carry" i.e. not portable.

I think the thing that makes me sure that you can have cord and plugged panels and distribution boxes down line from a generator without a ground rod is the use of the word equipment in 250.34 instead of the words utilization equipment.

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be grounded and shall be permitted to serve as the grounding electrode for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The non?current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
Equipment. A general term including material, fittings, devices, appliances, luminaires (fixtures), apparatus, and the like used as a part of, or in connection with, an electrical installation.
Utilization Equipment. Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes.
Also to me if they meant portable or vehicle mounted generators to be less then a certain size for this to apply why did they not simply say generators less then xxxxx watts, KW etc.?

JMO, Bob
The problem I have with this is that the generator is now supplying equipment through receptacles that are mounted somewhere other than on the generator.
--
Tom
 
Re: Portable Generators and Ground Rods

If the lightning strike jumped that far, and the vehicle frame was holding on to it, why wouldn't it jump another couple of inches across the vehicles battery since the frame is bonded to the negative terminal of the battery? Theoretically, the negative charge may just as well seek the positive charge at the other terminal of the vehicle battery and probably cause it to explode. Sound phoesible?

Rod
 
portable tool generators

portable tool generators

But what if the portable generator (I'm talking small here, like the kind you can run down the street with, while people are using it) has a label on it saying that it must be grounded. We all know that it doesn't, and, in fact, grounding it actually increases the number of possible ways that someone could get killed. If it has a label on it, does 110.3(B) require us to connect the portable generator to a Grounding Electrode System?

Currently, i am telling the electrical contractors to make sure the generators don't have this label on them before they bring them inside the plant. That way, there is no question that they don't have to ground them.
 
Wow this thread is mine from 3 years ago. 8)

Eric that is an interesting question and I would probably handle it like you are. :)

That said I do not believe I have ever seen a small portable generator saying it required grounding.

I would say it is grounded as the NEC says that the frame may serve as the grounding electrode.
 
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