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Old 06-30-2012, 05:30 PM   #16
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A discussion on the Proper grounding for portable generators


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Originally Posted by brric View Post
Please explain what an unfortunate mishap would involve.
Think about it, let's say a generator does contain a switch to unbond the neutral and grounding conductor, now let's say the user wants to use a receptacle on the generator, and a ground fault occurs in the appliance, the generator no longer contains ground fault protection and the user is hopefully only slightly shocked.

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Old 06-30-2012, 05:37 PM   #17
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A discussion on the Proper grounding for portable generators


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Originally Posted by AllanJ View Post
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?
Check out article 100 of the nec, sepretely derived systems.
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Old 06-30-2012, 05:48 PM   #18
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A discussion on the Proper grounding for portable generators


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Originally Posted by andrew79 View Post
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.
2011 NEC 702.11(A) and (B)
Doesn't say ground rod, says connected to GEC.

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Old 06-30-2012, 05:50 PM   #19
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A discussion on the Proper grounding for portable generators


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Originally Posted by stickboy1375 View Post
Think about it, let's say a generator does contain a switch to unbond the neutral and grounding conductor, now let's say the user wants to use a receptacle on the generator, and a ground fault occurs in the appliance, the generator no longer contains ground fault protection and the user is hopefully only slightly shocked.
That's a reason the bond should stay. I would like to know an unfortunate mishap occuring because the bond stays in place.
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Old 06-30-2012, 07:59 PM   #20
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A discussion on the Proper grounding for portable generators


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Originally Posted by stickboy1375 View Post
Read 250.30 in the nec, if the generator is in fact a sds, then it requires grounding.
i did read 250.30 and it does say the generator needs grounding, it doesn't say where though, I'd like to see where it says that it needs it's own ground rod and can't be tied into the house grounding system.
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Old 07-01-2012, 01:52 AM   #21
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A discussion on the Proper grounding for portable generators


I apologize for being so late to get back to the discussion. It's been a long day .....

I've read everyones reply and the good news is it is pretty much the same discussion you see on other professional forums. I'm not going to pretend that I am the knower of all things for grounding a portable genterator .. so that said all I can do is add to the discussion and try to tie in the NEC code to obtain some degree of clarity.

There are a couple things I agree with that some of you have mentioned that determines whether or not a portable generator requires earth grounding. Those are

1.) Is the generator a seperately derived system (SDS) not serving only cord and plug equipment or equipment mounted on the generator via the frame mounted receptacles

2.) Is the transfer device switching the grounded conductor of the utility to that of the generator.

Lets clarify the defintions of SDS and Service as they appear in the 2008 NEC

Quote:

Separately Derived System.
A premises wiring system whose power is derived from a source of electric energy or

equipment other than a service. Such systems have no direct
electrical connection, including a solidly connected
grounded circuit conductor, to supply conductors originating
in another system.

Service.

The conductors and equipment for delivering electric
energy from the serving utility to the wiring system of
the premises served



So a generator in order to be considered SDS must not have a solid or direct connection to any conductors of another system including the utility grounded conductor. So if the transfer device switches out the neutral and the ungrounded conductors then it would meet the defintion of an SDS.

On the flip side if the generator switches out the ungrounded conductors and not the neutral then it is a non separately system.

So the next question I would have is what are the grounding requirements of an SDS vs an non SDS ?

NEC 250.20(D)

Quote:

(D) Separately Derived Systems as covered in 250.20(A) or (B), shall be grounded as

specified in 250.30(A). Where an alternate source such as
an on-site generator is provided with transfer equipment
that includes a grounded conductor that is not solidly interconnected
to the service-supplied grounded conductor, the
alternate source (derived system) shall be grounded in accordance
with 250.30(A).


FPN No. 1: An alternate ac power source such as an onsite

generator is not a separately derived system if the
grounded conductor is solidly interconnected to a service supplied
system grounded conductor. An example of such
situations is where alternate source transfer equipment does
not include a switching action in the grounded conductor
and allows it to remain solidly connected to the service supplied
grounded conductor when the alternate source is
operational and supplying the load.




So I think it is clear using the NEC to see the differences for grounding a generator portable or otherwise.


1.) Your switching device (transfer switch) determines SDS .. ie .. if it switches the neutral from utility to generator it is SDS and is grounded in accordance with 250.30(A). If not then it is not grounded in accordance with 250.30(A)


If it is non SDS then 250.24(A)(5) applies and neutral and ground must not be bonded load side of the service equipment for the premise wiring system using the alternatge power source.

The interlock is a transfer device that does not switch the neutral of the utility to that of the generator and therefore it is not a SDS. A grounding electrode is not required but neutral and ground cannot be bonded load side of the homes service equipment 250.24(A)(5). So in the situation that was shown to us in the other thread is not SDS and would require that the neutral bond connection at the generator frame be broken and the homes grounding electrode system will remain connected to the service grounded conductor and the earth grounding at the utility transformer.

I see no way around breaking the neutral and ground bond at the generator to be compliant using a transfer device that does not switch the neutral such as an interlock.. The question is .. if that is the case why are instructions not included in the generator manual to inform you of that? It seems the manufactureres have been slow getting up to speed on this bit of information.

The question becomes if I don't unbond the generator at what risk to human safety do I incur?

I know that I have certainly created a parallel path with the utility grounded conductor and egc of the generator power cord between the homes service equipment and will certainly have neutral current imposed on it when I operate the generator in a standby application. But frankly I have a hard time seeing any more danger to touching the generator frame than touching the metal of the service equipment enclosure as both are bonded to the utility grounded conductor and the earth grounding at the service. The difference being the generator frame is being used as a conducting path where as the service equipment panel has no current on it. I actually can't remember when I saw a portable connected to a home via a transfer device that didnt switch the neutral that had the neutral and ground bond removed. And to this date I don't have any notification of a human mishap occurring because of it. I have been told that there is more danger if a ground rod is driven in this screnario than not.

Anyway I think Speedy and Brric are maintaining this idea and the generator should remain bonded and not tampered with. I tend to agree though I also believe it may be better/safer to find the right transfer switch or a generator that has neutral and ground unbonded.

Now someone needs to link me to a portable generator that has frame mounted receptacles with neutral and ground unbonded. Since to operate it woulod be to operate it without ground fault protection for human safety.... the ground path for fault current is open ..... ???

The only way that works for me is if that generator screams WARNING you need to bond the neutrtal and ground before operating cord and plug tools...... and when you do plug something into a receptacle it will not start with neutral and ground not bonded.

Hopes this in some way helps ... to summurize IMO the NEC is clear if the gen is SDS a ground rod is required if not SDS no ground rod required. The transfer switch determines this and to that I agree with Stickboy and Alan.



Last edited by Stubbie; 07-01-2012 at 02:00 AM.
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Old 07-01-2012, 06:34 AM   #22
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A discussion on the Proper grounding for portable generators


A ground fault circuit interrupter does not need a ground wire (equipment grounding conductor) to function properly.

We all know that if/when neutral and ground (EGCs) are connected in more than one place then neutral current will flow between these two points using both the neutral and the ground. In turn there will be a voltage drop across these two points or in other words the potential (voltage) between some points along the EGCs and a theoretical ground (something bonded to grounding electrode system with no fault current along that path) will be nonzero.

But for a running generator during a utility power outage the neutral at the generator is the "current sink" or ultimate destination of the current. Thus the generator frame is really not part of the current path. In other words the potential between the still N-G bonded frame and neutral will be zero. And the other point where neutral and ground were intentionally and deliberately left bonded is the neutral bus in the panel, and there the potential between neutral and theoretical ground is zero (and hazard free) because the GEC is connected there.

Let's imagine you had a ground rod for your generator (not the same ground rod that is part of the house grounding electrode system). This will put the earth at the generator at the same potential as the generator body. Because earth is not that great a conductor, the potential between different places, even just a few feet apart, can be measurable depending on presence of current flowing from one grounding electrode to another, due to abnormal conditions. If ground and neutral were left connected both at a generator and at the house panel, then connecting the generator to a ground rod will not change any voltage drop along the EGC between generator and panel by much since very little current will take the third sharable path, the earth.

If the generator has a N-G bond that is intended to be removed, that bond should be in place or removed depending on the needs of the system being energized. (Removed if the panel being fed has N-G bonded.)

* Fault current -- An unwanted current flow resulting from an energized object coming into contact with another object when it should not.
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Old 07-01-2012, 10:08 AM   #23
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A discussion on the Proper grounding for portable generators


i've spent awhile getting familiar with the nec(2012) and i came across this exception in 7.30(4)
Exception No. 2 to (1) and (2): If a separately derived
system originates in listed equipment suitable for use as
service equipment, the grounding electrode used for the
service or feeder equipment shall be permitted as the
grounding electrode for the separately derived system.
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Old 07-01-2012, 12:58 PM   #24
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A discussion on the Proper grounding for portable generators


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Originally Posted by andrew79 View Post
i've spent awhile getting familiar with the nec(2012) and i came across this exception in 7.30(4)
Exception No. 2 to (1) and (2): If a separately derived
system originates in listed equipment suitable for use as
service equipment, the grounding electrode used for the
service or feeder equipment shall be permitted as the
grounding electrode for the separately derived system.
Where ould I find 7.30(4)? There is no 2012 NEC.
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Old 07-01-2012, 02:21 PM   #25
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A discussion on the Proper grounding for portable generators


sorry it says 2011, 2012 is my canadian book. I've got too many laying around lol. let me know if there's no 2011, i looked in the 08 and couldn't find it.
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Old 07-01-2012, 03:45 PM   #26
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A discussion on the Proper grounding for portable generators


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sorry it says 2011, 2012 is my canadian book. I've got too many laying around lol. let me know if there's no 2011, i looked in the 08 and couldn't find it.
There is no NEC article 7.30 anyhere, any year for at least the last 20 years.
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Old 07-01-2012, 07:15 PM   #27
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A discussion on the Proper grounding for portable generators


again my bad, it's been a long weekend, 250.30(4) exception number two. Don't ask how i got 730 out of that because i don't know. and it is in the 2008 version just down a little farther.
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Old 07-03-2012, 01:33 PM   #28
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A discussion on the Proper grounding for portable generators


So I'm guessing this thread is derived from my plea for help determining how/if to run the neutral and ground connections from my generator to my main power panel.

Based on the discussion in that thread and this one, I think I have an idea of how to do this, but PLEASE correct me if I'm wrong.

I've attached an amended copy of my wiring diagram. Basically, my understanding is that I should ground the generator outside, per the owner's manual, but only tie the generator neutral to the power panel's neutral bus, but not the ground connection, since the generator has an NG bond that's not easily removed, and since ground and neutral are already bonded in the panel.

Am I missing anything here?
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Old 07-03-2012, 09:07 PM   #29
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A discussion on the Proper grounding for portable generators


It's wrong but I won't correct you. I would do it that way too assuming the generator is portable.

We may have a generator whose N-G bond can't be easily removed, and a main panel which we do not want to revamp, unbonding N-G. Ergo N-G remains bonded in both places which is not proper. A transfer switch that switches the neutral won't make any difference here.

I would just grab a patch cable and connect it all together.

Untying the ground wire between generator and panel is needed only if a GFCI trips otherwise.
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Old 07-03-2012, 10:45 PM   #30
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A discussion on the Proper grounding for portable generators


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It's wrong but I won't correct you. I would do it that way too assuming the generator is portable.
Yes, it's a portable generator. Why is this wrong? Not saying it isn't wrong, just wondering what's wrong with it and why you'd do it this way too if it's wrong.

Quote:
Originally Posted by AllanJ View Post
We may have a generator whose N-G bond can't be easily removed, and a main panel which we do not want to revamp, unbonding N-G. Ergo N-G remains bonded in both places which is not proper. A transfer switch that switches the neutral won't make any difference here.

I would just grab a patch cable and connect it all together.
Connect all what together?

Quote:
Originally Posted by AllanJ View Post
Untying the ground wire between generator and panel is needed only if a GFCI trips otherwise.
But doesn't connecting the ground from the generator to the panel risk putting current potential on the ground line because of two N-G bonds? Is whether the GFCI trips really the main concern here? Above you indicate it's improper to bond N-G at both ends, but here you'd do it, but only if it didn't trip the GFCI?

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