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Grounding a Generator

Posted by pawprint1 (My Page) on
Tue, Jul 31, 12 at 17:51

How do I ground my generator?

The manual is not very specific but suggests that a generator should be grounded. It mentioned grounding rods or call an electrician.

I've searched the internet and YouTube, I've found lots of good information on generators, and most say to ground it, but that's it.

Do I need to buy a copper wire and tie it to something metal? Is it really that difficult? Thoughts? Advice?
Thank you.

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Follow-Up Postings:

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RE: Grounding a Generator

There's a grounding lug on that thing. It needs to be grounded to the grounding system of whatever it is feeding (typically your home grounding rods).


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RE: Grounding a Generator

Out of curiosity, does the ground wire that makes up the 4-wire or 3-wire connection to the home (assuming either a 4-wire NEMA twist lock socket or a 3-wire) perform the same function?


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RE: Grounding a Generator

The problem is that many generators bond their neutral and ground together internally.

While this is required for stand alone operation (along with a ground rod) the bond needs to be removed if you are connecting to house wiring since it already connects ground and neutral, and you end up with neutral current on the ground conductor from the panel to the generator.


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RE: Grounding a Generator

As long as you are using the front panel receptacles to feed whatever it is your feeding you DO NOT have to connect to any grounding electrodes or the grounding electrode of the house.


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RE: Grounding a Generator

Petey: the NEC would disagree with you as does the manufacturer.


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RE: Grounding a Generator

Every generator I have ever seen calls for a grounding electrode, though vanishingly few folks seem to instal them.

The other problem is that it likely already has a bond from frame ground to neutral, and this must be removed to hook up to a house.


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RE: Grounding a Generator

Ron, please show me.

Sorry, I disagree with you guys.


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RE: Grounding a Generator

The manual says to ground the generator via the lug provided. They don't provide information. As for the NEC Art. 702.11


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RE: Grounding a Generator

Weedmeister wrote: Out of curiosity, does the ground wire that makes up the 4-wire or 3-wire connection to the home (assuming either a 4-wire NEMA twist lock socket or a 3-wire) perform the same function?

I, too, am interested in the answer to this question. It seems to me that this connection amounts to a sound bonding to the (house) grounding system. Even during a power failure, this should provide reasonable connectivity to earthed electrodes.

I realize that this may cause issues of unequal potentialities (e.g., the same essential reason neutrals and grounds are not bonded at subpanels), but is this really an important distinction?

If you remove the neutral-ground bond at the generator, the neutral of the house wiring still remains bonded to ground at the system bonding point (i.e., usually but not always the main panel). At the risk of muddying the waters, I must admit that I've never fully understood the implications of two independently derived power sources with connected neutrals. (That is, how does this work when the generator powers some circuits and the grid powers other circuits? Keep in mind that most home transfer switches segregate the hots but not the neutrals.)


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RE: Grounding a Generator

The reason for separating the ground and neutral is simply to guarantee that the ground wire will not be carrying any current except during a wiring fault. So basically, you need to treat the generator just like you would a subpanel in a separate building...a 4 wire circuit for connectivity with the main panel, the neutral and ground separated at the generator, and a ground rod driven at the generator.


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don't forget

Just a reminder that you also need a disconnect switch if you are going to connect to your household electrical system.


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don't forget

Just a reminder that you also need a disconnect switch if you are going to connect to your household electrical system.


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RE: Grounding a Generator

kurto wrote: The reason for separating the ground and neutral is simply to guarantee that the ground wire will not be carrying any current except during a wiring fault.

So long as there are no older three-wire circuits (e.g., range, dryer or outbuilding) using the neutral as equipment ground, this is true. Otherwise, it's a matter of differing potentialities.

So basically, you need to treat the generator just like you would a subpanel in a separate building...a 4 wire circuit for connectivity with the main panel, the neutral and ground separated at the generator, and a ground rod driven at the generator.

That's surely one way to look at it. The other way (at least when the generator is the only source of power) is to view it as a bonding of ground and neutral at the most distant subpanel only.


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RE: Grounding a Generator

"That's surely one way to look at it. The other way (at least when the generator is the only source of power) is to view it as a bonding of ground and neutral at the most distant subpanel only."

That is NO how it is done, generator or not.
The bond is at the first panel (or switch) from the power source.

The NEC requirement is for a single bond in the main panel of the service.

Unless you plan on disconnecting this bond, you already have the bond present and it should NOT be repeated at a generator.

You are replacing the POCO as the source of power.

the POCO does NOT supply a grounding conductor.
they supply a grounded conductor (AKA neutral) tat s part of the current carrying wiring.

The grounding conductor is fr safety, and ONLY caries current when a fault occurs in the rest of the wring (or something hooked to the wring to get power, (AKA 'utilization equipment').

You do not need a rod at the generator, just NO BOND between ground and neutral at that point.

Just as with the POCO, the service ground rods are fine.

If you add another rod you must bond it to the already existing rods (and a plug does not qualify for bonding grounding systems).


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RE: Grounding a Generator

Thanks for prolix lecture, Brick. You didn't touch the issue of the interconnected neutrals when two power sources are present, but then I didn't really expect to learn anything about that. It's just too arcane.

The bond is at the first panel (or switch) from the power source.

And when the only power source is the generator? It seems to me that the underlying principle is simply ignored (or outright violated?) because, you know, the generator isn't the permanent house wiring. Or something.

Hmmm, and while we're at it, compare and contrast:

On 8/2 Brick wrote: Every generator I have ever seen calls for a grounding electrode, though vanishingly few folks seem to instal them.

On 8/5 Brick wrote: You do not need a rod at the generator, just NO BOND between ground and neutral at that point.

I'm sure it's just me. (In truth, it's because the generator manufacturers are also flummoxed by the problem of providing concrete and practical advice to homeowners.)

The reality is that a lot of folks (I'd include myself) have a portable generator that is sometimes used as a completely independent power source at a remote site, but is sometimes used (via a transfer switch, we hope) to supply power to a few circuits in the house in the event of a power outage.

I can honestly say that I don't know a single soul (including a few electrician friends) who finagles the generator bond every time the generator is repurposed. Not one! And I've never seen a portable generator installation manual that emphasizes the importance of performing this oh-so-important task.

So let me see if I've got this right. If we were to accept kurto's analogy to a subpanel in a detached building (i.e., earthed electrode required, but EG not bonded to neutral), I guess we have a problem because the plug does not qualify as a method of bonding the remote EG to the system ground. That is, we now have two grounding systems that are only loosely -- but not reliably -- connected in a manner meeting NEC specifications.

In the case of a a power source from a generator or inverter, what makes a neutral a neutral (instead of just an opposing hot) is the bond to earth. (In at least some designs, either pole could be selected to become the neutral.) In my view, this means that if the continuity of the neutral is ever broken (or seriously impeded) in the extremities of the circuit, the neutral effectively becomes hot.

(Yeah, I know, there aren't supposed to be any switched neutrals. But who's going to guarantee that everything plugged into a receptacle has the correct polarity?)

The point is that, notwithstanding the strict application of the code, neither "solution" conforms to a purist's model.

All of which brings us back to my original question: is it really important?

Honestly, I have no particular problem relying on the plug to provide my connection to the system ground. And, frankly, I'd just as soon have the neutral bonded to ground at the earliest point, even if it is redundant of the bond at the main panel. In my view, the potential problems are no greater than those caused by the existence of a three-wire 240-volt appliance in my house.


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RE: Grounding a Generator

Ok. If the plug does not supply the ground, is it permitted and/or advisable to connect the ground lug on the generator (assuming it has one) to the ground rod of the house (with a sufficiently sized cable and clamps)?

Secondly, I have a Big Red Book that (supposedly) explains the NEC 2011 code. In the section about stand-by power, it seems to imply that the 2011 code requires that the neutral be switched along with the two hots when a stand-by generator is used. [I know these are not the correct terms.]
Is this true or does it only apply to permanently installed generators with automatic transfer switches?


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RE: Grounding a Generator

Hi,

Generator grounding is often confusing because it is (a) Generator (b) site and (c) Transfer switch specific. There are a number of things to bear in mind, (1) Bonding of Neutral to ground (2) Switched Neutral and (3) grounding (or lack of it) of circuits that the generator is hooked up to.

In a nutshell, depending on these three "Conditions" there is a right way to do it. Some generators have bonding tags so you can change the bonding. Some Transfer switches switch the neutral others do not. Some uses have no circuits grounded, e.g. running a power drill on a work site. Others there are other grounds, e.g. hooking up to a house which already has a ground.

So rather than try and explain this in a short confusing message, there are two I think rather good papers on this subject by Cummins Power, the generator company.

http://www.cumminspower.com/www/literature/technicalpapers/PT-6005-GroundingAC-1-en.pdf

http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf

Especially in paper 2, they explain the correct mix of these three conditions for safe operation of a generator. I.E. depending on site and equipment details, what the correct thing to do is.

Warmest regards, Mike.

Here is a link that might be useful: Bonding, Grounding Switching Neutrals


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RE: Grounding a Generator

"I can honestly say that I don't know a single soul (including a few electrician friends) who finagles the generator bond every time the generator is repurposed. Not one! And I've never seen a portable generator installation manual that emphasizes the importance of performing this oh-so-important task. "

What you do or do not do does not affect what the NEC says.

Portable generators have different rules than a generator powering a structure.

If you choose not to obey the applicable rules when using the device for different applications that is your problem (and possible liability).

A generator being used in aportable application has neutral and ground bonded and requires a ground rod under the NEC.

A generator feeding a required transfer switch for structure is no longer being used as a 'portable' device, and the bond is accomplished by the structure wiring and should not be repeated in the generator for safety.

Grounding electrode systems are NOT there for personnel protection.
The impedance of the earth is way to high to reliably have 120 V trip an overcurrent device.

If you leave the bond in the generator, and then bond again in the service, the generator frame is at some arbitrary voltage based on leakage and current sharing between the grounded and grounding conductors.

It is more than capable of generating a high enough voltage to be lethal.
While the earth impedance may not allow 15 amps to flow, that is well over the level needed to disrupt your heart and kill you.


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RE: Grounding a Generator

http://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf


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RE: Grounding a Generator

OSHA only applies to job sights.


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RE: Grounding a Generator

I understand that. Does this document describe best practices for portable generator operation?


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RE: Grounding a Generator

The NEC describes the best practices for what the original poster described. Optional (i.e., not circuits required to have continual power), portable generator use was already referenced here. In addition the manual references grounding as being required which also makes it binding as the code (though they lack details on how other than connecting to the stud provided you would accomplish this).


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