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Old 06-30-2012, 02:22 AM   #1
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A discussion on the Proper grounding for portable generators


There are 3 areas for grounding portable generators. 1.) When the generator is used as a power source at a job site and only cord and plug loads are used. 2.) When the generator is vehicle mounted and 3.) When the portable generator is used for stand by power for a homes premise wiring.

250.34(A) covers the first one but remember there can be local jurisdictional amendments that require a ground rod at the generator and the frame will not satisfy local code for the grounding electrode..

Ok .. I started ... I'll add more later but I'm past my time to get some sleep. Lets keep it civil and have a professional discussion. We won't agree at first but I think in the end it will be clear.


Last edited by Stubbie; 06-30-2012 at 02:33 AM.
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Old 06-30-2012, 06:40 AM   #2
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A discussion on the Proper grounding for portable generators


Consider the following situation: I have a portable generator that may be connected to the home wiring via an extension cord plugging onto a male receptacle (inlet) on the side of the house. Here are the constraints I will impose:

1. The main panel will not be modified to separate grounds and neutrals.
2. The generator will not be modified in a destructive or warranty-voiding manner.

We can imagine a poll question (use replies as opposed to a real forum poll question) as to choosing do-able (not necessarily kosher) workarounds.

(Some generators have an exposed ground/neutral bond to be in place for field use and removed for home wiring use to satisfy the conditions above.)

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Last edited by AllanJ; 06-30-2012 at 06:48 AM.
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Old 06-30-2012, 07:18 AM   #3
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A discussion on the Proper grounding for portable generators


IMO, a portable generator that uses only the receptacles built into the unit to provide power, even to a structure, does NOT require a grounding electrode, and the neutral/ground bond should remain in place as it is from the factory.
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Old 06-30-2012, 07:43 AM   #4
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A discussion on the Proper grounding for portable generators


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Originally Posted by Speedy Petey View Post
the neutral/ground bond should remain in place as it is from the factory.
Some generator manufacturer's provide instructions for removing the bond and new labeling to place on the generator.
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Old 06-30-2012, 07:50 AM   #5
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A discussion on the Proper grounding for portable generators


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Some generator manufacturer's provide instructions for removing the bond and new labeling to place on the generator.
Ahhh, good to know. I was not aware of this.

Even so, if only receptacles are used on the genset the bond should still remain in place. DO you agree?
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Old 06-30-2012, 07:52 AM   #6
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A discussion on the Proper grounding for portable generators


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Originally Posted by Speedy Petey View Post
Ahhh, good to know. I was not aware of this.

Even so, if only receptacles are used on the genset the bond should still remain in place. DO you agree?
For the obvious safety reasons, yes. We both know these generators are never just going to be used at a structure.

Last edited by stickboy1375; 06-30-2012 at 07:55 AM.
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Old 06-30-2012, 10:34 AM   #7
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A discussion on the Proper grounding for portable generators


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Originally Posted by stickboy1375 View Post
For the obvious safety reasons, yes. We both know these generators are never just going to be used at a structure.
So at this point you would think that the adjustments need to be made on the house tie in side to avoid having to take out and replace the bond wire in the genny every time you use it for a different application.

I've done some searching and the only thing i can find on actually driving in a ground rod at the genny location is that it's suggested only if the distance is far from the house, otherwise it should be tied into the house grounding system to keep the same potential. Don't have a code reference on it just searched threads from other forums. What they suggest if the genny is a long distance out is to drive a ground rod in and bond the case to the ground rod. I can see why they say this as you don't want a potential difference between your two ground points but i can't see why anyone would want to install a genny far enough from a house that it would make a difference

so assuming that we can't modify the ground then that leaves us with the option of switching the neutral out to break the n/g bond. my reasoning on not switching out the ground is that if you disconnect the house ground and your house gets hit by lightning(a storm is usually when we have a genny on) that the genny ground probably isn't going to be able to handle that sort of jolt.
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Last edited by andrew79; 06-30-2012 at 10:48 AM.
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Old 06-30-2012, 10:46 AM   #8
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A discussion on the Proper grounding for portable generators


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I've done some searching and the only thing i can find on actually driving in a ground rod at the genny location is that it's suggested only if the distance is far from the house, otherwise it should be tied into the house grounding system to keep the same potential. Don't have a code reference on it just searched threads from other forums. What they suggest if the genny is a long distance out is to drive a ground rod in and bond the case to the ground rod. I can see why they say this as you don't want a potential difference between your two ground points but i can't see why anyone would want to install a genny far enough from a house that it would make a difference
If the generator truly is a SDS, then article 250.30 takes place... as a side note, if the generator is not a SDS, and is remotely located and you still want to drive a ground rod, then at that point it is an auxiliary ground rod, and maybe will help with a lightning strike?
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Old 06-30-2012, 10:54 AM   #9
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A discussion on the Proper grounding for portable generators


The way I see it, you have two options when wiring a portable generator to to a structure, this all depends on the generator you purchase,

IF the generator does contain a N-G bond, then you MUST switch the grounded (neutral) conductor at the transfer switch, making the generator a SDS by definition and article 250.30 now applies and ground rods are required.

IF the generator contains a floating grounded (neutral) conductor, then you can use a standard 2-pole transfer switch and have a solidly grounded (neutral) circuit connection, and NOT require a ground rod at the generator.
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Old 06-30-2012, 10:57 AM   #10
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A discussion on the Proper grounding for portable generators


Quote:
Originally Posted by andrew79 View Post
So at this point you would think that the adjustments need to be made on the house tie in side to avoid having to take out and replace the bond wire in the genny every time you use it for a different application.

I've heard of some generators that just contain a switch on the unit for this purpose.

just stating, not directing this comment,

Look how difficult this is for professionals to understand, you think mr. smith is going to know the difference between the two? or care for that matter? Because it will work either way... until an unfortunate mishap takes place.

Last edited by stickboy1375; 06-30-2012 at 11:14 AM.
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Old 06-30-2012, 02:15 PM   #11
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A discussion on the Proper grounding for portable generators


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Originally Posted by stickboy1375 View Post
I've heard of some generators that just contain a switch on the unit for this purpose.

just stating, not directing this comment,

Look how difficult this is for professionals to understand, you think mr. smith is going to know the difference between the two? or care for that matter? Because it will work either way... until an unfortunate mishap takes place.
Please explain what an unfortunate mishap would involve.
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Old 06-30-2012, 02:48 PM   #12
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A discussion on the Proper grounding for portable generators


Quote:
Originally Posted by stickboy1375 View Post
The way I see it, you have two options when wiring a portable generator to to a structure, this all depends on the generator you purchase,

IF the generator does contain a N-G bond, then you MUST switch the grounded (neutral) conductor at the transfer switch, making the generator a SDS by definition and article 250.30 now applies and ground rods are required.

IF the generator contains a floating grounded (neutral) conductor, then you can use a standard 2-pole transfer switch and have a solidly grounded (neutral) circuit connection, and NOT require a ground rod at the generator.
just to play devils advocate here but if the genny is close to the house and you've switched out the neutral and left the ground tied in then it is still grounded through your house grounding system and therefore you shouldn't need a ground rod. I don't have a copy of the nec but if the part i found on google is a direct copy then it doesn't say in that article that a separate ground rod needs to be driven just that it needs to have a ground to earth to stabilize the voltages. If there's a section that says it does need a ground rod then please post it so i can file it away in my "obscure code references folder" on my pc. Even stuff i've found myself sometimes i can never find again in the code book lol.
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Old 06-30-2012, 04:49 PM   #13
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A discussion on the Proper grounding for portable generators


What I am leaning towards is not always having a separate continuous equipment grounding conductor between generator and panel being fed, which permits using any kind of transfer that is otherwise legal, and rolling up any kind of portable generator to the inlet receptacle on the side of the house.

(copied from another forum) Because no current flows in the generator to house panel lines when the transfer is set to utility power, there cannot be any voltage drop in that neutral and for a generator whose ground and neutral are permanently bonded, the voltage at the generator body is zero relative to the house grounding electrode conductor (the latter and the generator neutral are connected to the panel neutral bus). Should a ground fault occur somewhere in the house wiring, that would be resolved at the house panel neutral bus.
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Last edited by AllanJ; 06-30-2012 at 05:06 PM.
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Old 06-30-2012, 05:02 PM   #14
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A discussion on the Proper grounding for portable generators


Open question, if the only connection between current carrying conductors in the generator subsystem and current carrying conductors in the utility system is the single connection of the neutrals respectively meeting together with the grounding electrode conductor at the neutral bus bar in a panel, why would the generator system not be considered separately derived?
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Old 06-30-2012, 05:22 PM   #15
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A discussion on the Proper grounding for portable generators


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just to play devils advocate here but if the genny is close to the house and you've switched out the neutral and left the ground tied in then it is still grounded through your house grounding system and therefore you shouldn't need a ground rod. I don't have a copy of the nec but if the part i found on google is a direct copy then it doesn't say in that article that a separate ground rod needs to be driven just that it needs to have a ground to earth to stabilize the voltages. If there's a section that says it does need a ground rod then please post it so i can file it away in my "obscure code references folder" on my pc. Even stuff i've found myself sometimes i can never find again in the code book lol.
Read 250.30 in the nec, if the generator is in fact a sds, then it requires grounding.

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