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Old 07-03-2012, 11:46 PM   #31
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A discussion on the Proper grounding for portable generators


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Originally Posted by tjnoff View Post
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?
If you follow the NEC the ground rod at the generator is not needed. You only need a connection to the grounding electrode for the service to your home. This would be the connection of your equipment ground and neutral in the wiring from the generator to the neutral bar in the homes service panel in your drawing. Unless your transfer switch (in your case the interlock) switches the service neutral out and you have no soild connection to the neutral in the wiring coming from your generator then you do not have a seperately derived system and grounding the generator with a ground rod is not required.
The probelm arises from the neutral and ground bond at the generator. This is not allowed because objectionable current will flow on the equipment ground wire in the generator cord as it is in parallel with the neutral current returning to the source (generator).
This was addressed for years in the manufacturer manuals with " should be wired by a licensed electrician". It's problematic becasue portable generators need neutral to ground bonding to safely operate cord and plug power tools from the receptacles mounted on the portable generator.

So to clarify your drawing .... the ground rod isn't required at your generator (it is not a seperately derived system). But the NEC also does not allow the neutral to ground bond at the generator unless it is a Seperately Derived power source..

I would not provide earth grounding of the generator with the ground rod in your drawing. Frankly I'm not sure what to tell you about the neutral to ground bond at the generator. Your first drawing in the other thread would be how 99% of most homeowners would operate and ground the generator. IMO the risk is minimal in doing so, just the same I don't like the idea of current on the ground wire.

I remember somewhere a drawing that expalined the hazard I'll see if I can locate it and provide a link.


Last edited by Stubbie; 07-04-2012 at 12:07 AM.
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Old 07-04-2012, 07:47 AM   #32
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A discussion on the Proper grounding for portable generators


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Yes, it's a portable generator.

1. Why is this wrong? Not saying it isn't wrong, Just wondering what's wrong with it and

2. Why you'd do it this way too if it's wrong.

3. Connect all what together?

4. 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?

5. 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?
1. Because ground and neutral should not be bonded in two places per the NEC.

2. Saves having to mutilate the generator or redo the main panel just to get things working in a situation that is temporary (like a power outage).

3. As shown in your diagram, connecting the patch cord from the generator to the inlet on the side of the house as 99% of other homeowners do.

4. I do not see any hazard. Since the generator is the power source, electricity on the equipment grounding conductor is not going to be using your body to get back to the power source. No different than a generator out in the field (its N-G should be bonded). IMHO the multiple N-G bondings and current on the EGC is the least of the evils.

5. If the generator GFCI trips then you don't have electricity. So I suggested a workaround of not having an unbroken EGC such as using a patch cord with just two hots and neutral.

6. Even if a licensed electrician installs the generator and connects up the patch cord, he will have the same dilemma if that generator did not have an easily removed N-G bond. Incidentally many whole house transfer switches (as opposed to back feed breakers and mechanical interlocks) require unbonding N-G in the panel. And I would recommend restructuring things to have just one N-G bond if you have a permanently installed generator.
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Old 07-04-2012, 09:29 AM   #33
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A discussion on the Proper grounding for portable generators


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Originally Posted by stubie View Post
If you follow the NEC the ground rod at the generator is not needed. You only need a connection to the grounding electrode for the service to your home. This would be the connection of your equipment ground and neutral in the wiring from the generator to the neutral bar in the homes service panel in your drawing. Unless your transfer switch (in your case the interlock) switches the service neutral out and you have no soild connection to the neutral in the wiring coming from your generator then you do not have a seperately derived system and grounding the generator with a ground rod is not required.
The probelm arises from the neutral and ground bond at the generator. This is not allowed because objectionable current will flow on the equipment ground wire in the generator cord as it is in parallel with the neutral current returning to the source (generator).
This was addressed for years in the manufacturer manuals with " should be wired by a licensed electrician". It's problematic becasue portable generators need neutral to ground bonding to safely operate cord and plug power tools from the receptacles mounted on the portable generator.

So to clarify your drawing .... the ground rod isn't required at your generator (it is not a seperately derived system). But the NEC also does not allow the neutral to ground bond at the generator unless it is a Seperately Derived power source..

I would not provide earth grounding of the generator with the ground rod in your drawing. Frankly I'm not sure what to tell you about the neutral to ground bond at the generator. Your first drawing in the other thread would be how 99% of most homeowners would operate and ground the generator. IMO the risk is minimal in doing so, just the same I don't like the idea of current on the ground wire.

I remember somewhere a drawing that expalined the hazard I'll see if I can locate it and provide a link.
I included the ground rod in the latest drawing because I was getting the impression that I should float the ground line between the portable generator and the panel. I figured the generator needed to be grounded somewhere.

However, I'm now thinking that the safest solution is to:
  • Connect the generator ground and neutral lines all the way to the panel's neutral bar, as in my first drawing;
  • Unbond ground and neutral at the generator. I do not plan to use this generator for field work to power tools (as a SDS?). It was purchased strictly as a home backup, although a very obvious reminder label on the generator about reconnecting the bond for SDS use is definitely in order, just in case. The NG bond is just a wire, although I don't know yet how hard it is to get to. If easily accessible, I could reconnect it for field work or warranty repair;
  • NOT ground the generator to a ground rod.

Does this plan afford the safest solution, in your opinion?

The hazard drawing would be helpful, thank you!
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Old 07-04-2012, 11:33 AM   #34
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A discussion on the Proper grounding for portable generators


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I
  • Connect the generator ground and neutral lines all the way to the panel's neutral bar, as in my first drawing;
  • Unbond ground and neutral at the generator. I do not plan to use this generator for field work to power tools (as a SDS?). It was purchased strictly as a home backup, although a very obvious reminder label on the generator about reconnecting the bond for SDS use is definitely in order, just in case. The NG bond is just a wire, although I don't know yet how hard it is to get to. If easily accessible, I could reconnect it for field work or warranty repair;
  • NOT ground the generator to a ground rod.

Does this plan afford the safest solution, in your opinion?
!
Yes this is a correct and safe solution and is probably the best.

Because the generator has a label mentioning reconnecting the N-G bond, that would mean that the bond was intended to be disconnected depending on the need, and everything works fine that way. If you have to unscrew a panel on the generator as described in the instructions, that is okay too.
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Old 07-04-2012, 01:40 PM   #35
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A discussion on the Proper grounding for portable generators


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Yes this is a correct and safe solution and is probably the best.

Because the generator has a label mentioning reconnecting the N-G bond, that would mean that the bond was intended to be disconnected depending on the need, and everything works fine that way. If you have to unscrew a panel on the generator as described in the instructions, that is okay too.
No, the label would be something I would add. Sorry I wasn't clear on that.

So looking at the owner's manual (http://www.generac.com/genApps/Libra...delnbr=0057980), page 8, section 2.4.3 looks to me to address the NG bonding. The upper image is for my generator. So I'm assuming that the two wires mentioned here would need to be disconnected. Am I reading this correctly?
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Old 07-04-2012, 04:40 PM   #36
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A discussion on the Proper grounding for portable generators


Remove those wires and then check for continuity between the neutral and ground at the outlets. No continuity means you are good to go. If you still have neutral-ground continuity then there is still another jumper that needs to be disconnected. FYI, I have seen a lot of generators with a jumper on the L14-30 outlet between the neutral and ground.
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Old 07-04-2012, 09:36 PM   #37
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A discussion on the Proper grounding for portable generators


My new 4-wire generdryer conforms to the NEC.

A discussion on the Proper grounding for portable generators-generdryer.jpg
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Old 07-05-2012, 08:20 AM   #38
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A discussion on the Proper grounding for portable generators


OK, thanks to everyone for sticking with this complicated issue. Once I get all of my parts, I will piece this together and test it. I will post my results here.
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Old 07-05-2012, 08:22 AM   #39
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A discussion on the Proper grounding for portable generators


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My new 4-wire generdryer conforms to the NEC.

Attachment 53527
Well, heck... if I'm gonna put a dryer outside the house, I may as well put an old Buick out there on cinder blocks and make a real generator out of the V8!
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Old 07-05-2012, 08:53 PM   #40
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A discussion on the Proper grounding for portable generators


the place where my father works was once owned by a genius born in the wrong town at the wrong time of the century, He built a genny out of a 8 cylinder ford from spare parts that runs a house and a hardware store/convenience store at the same time. It's something else to see. Next time i'm home i'll take some pictures and post them. It looks like something out of a jules verne novel. It may actually be old enough to be in them too
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Old 07-05-2012, 09:16 PM   #41
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A discussion on the Proper grounding for portable generators


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He built a genny out of a 8 cylinder ford from spare parts that runs a house and a hardware store/convenience store at the same time. It's something else to see. Next time i'm home i'll take some pictures and post them. It looks like something out of a jules verne novel. It may actually be old enough to be in them too
Did it have a voltage regulator? Or were the loads it served not that sensitive to varying voltage, such as incandescent lights a little under-voltaged and motors not at maximum loading?
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Old 07-05-2012, 10:15 PM   #42
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A discussion on the Proper grounding for portable generators


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Did it have a voltage regulator? Or were the loads it served not that sensitive to varying voltage, such as incandescent lights a little under-voltaged and motors not at maximum loading?
it's regulated, runs three ice cream freezers, a bunch of fridges, flourescent lighting, Alarm system. He built the regulator himself, don't ask me how, i've never gotten a good enough look at it to even start to figure out everything he's got in there.

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