Generator: Floating the neutral

21974 Views 30 Replies 12 Participants Last post by oncall, Dec 8, 2012

AdamBNYC

Discussion Starter · Dec 6, 2012

Hello Pro's,

As part of my generator project, I have started reading alot about floating the neutral from the generator. I'd like to make sure I understand this correctly and I have a few questions. Once again, thanks in advance

Quick review of my proposed solution
30 amp 220 breaker with interlock kit in the load panel
connected via 10/3 to a reliance inlet box 14-30 twist
10/3 "extension" cable from Generator to inlet box

From my understanding the generator I am to soon receive has a bonded neutral to the frame (briggs elite 7000). The problem being is that one should not have a bonded neutral to ground in two spot. in my case, one being in the load center and one being in the generator.

From what I am told I can expect is that there is a wire in the generator on one of the 120v outlets that bridges the ground to neutral. It is my understanding that I should remove this wire when backfeeding into the load center and put this wire back if i ever use it stand alone (which will be never)

Does this sound correct so far?
Do I need to ground the generator after this step, or will the generator use my in-house ground?
If I give a 120v extension from the generator to my neighbor to power his fridge, will it be a problem with the floating neutral?

Im sure I will think of some other questions. Thanks in advance!

1 - 20 of 31 Posts

Billy_Bob

· #2 · Dec 6, 2012

Lots of reading on that subject! Search google.com for the words...

separately derived system generator

non-separately derived system generator

neutral switching transfer switch

osha generator gfci

osha generator grounding

Julius793

· #3 · Dec 6, 2012

No you leave the generator exactly as it was manufactured hook it up when you need and go on with life.

AllanJ

· #4 · Dec 6, 2012

The typical home has the main panel neutral and ground bonded.

Check the generator instructions on how to unbond neutral and ground within. If you don't find that information, then skip that step, go on to the next step, and connect up the generator.

Julius793

· #5 · Dec 6, 2012

AllanJ said:
The typical home has the main panel neutral and ground bonded.

Check the generator instructions on how to unbond neutral and ground within. If you don't find that information, then skip that step, go on to the next step, and connect up the generator.

NO you do NOT unbound neural and ground by the generator!

Auger01

· #6 · Dec 6, 2012

AdamBNYC said:
Does this sound correct so far?

Yes. That is the right way to do it.

AdamBNYC said:
Do I need to ground the generator after this step, or will the generator use my in-house ground?

No. The generator is connected to the house ground via the power cord.

AdamBNYC said:
If I give a 120v extension from the generator to my neighbor to power his fridge, will it be a problem with the floating neutral?

If the generator is hooked up to your house, then it is fine to use an extension cord to the neighbor. Remember, the neutral and ground of the generator are still connected at the house panel, just be sure not to unplug it from the house.

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Julius793

· #7 · Dec 6, 2012

Ok now that I got home.... To prove my point that the frame of the generator MUST be bonded to neutral look at 250.34

stickboy1375

· #8 · Dec 6, 2012 (Edited)

Julius793 said:
NO you do NOT unbound neural and ground by the generator!

Technically, it is the correct way to do a generator installation. You cannot bond the neural and ground in more than one location, so you would either need a transfer switch that disconnects the neutral connection, or you would have to do it at the generator manually.

Personally, since the death rate is zero for not disconnecting the neutral/ground bond at the generator, I recommend leaving it alone, and moving on.

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AdamBNYC

Discussion Starter · #9 · Dec 6, 2012 (Edited)

Julius793 said:
Ok now that I got home.... To prove my point that the frame of the generator MUST be bonded to neutral look at 250.34

250.30 is contrary to what your saying

250.30 - CAUTION: The neutral-to-ground connection for a separately derived system cannot be made at more than one location. To do so would create multiple neutral-to-ground connections, which produces multiple neutral current return paths to the grounded (neutral) conductor of power supply, which can create a fire, shock hazard as well as power quality problems from electromagnetic interference. See 250.6 and 250.142(A).

250.34 Generators-Portable and Vehicle-Mounted
(A) Portable Generators. The frame of a portable generator is not be required to be grounded to the earth if:
(1) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.

(B) Vehicle-Mounted Generators. The frame of a portable generator is not required to be grounded to the earth if:
(1) The generator frame is bonded to the vehicle frame.
(2) The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(3) The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.

FPN: Portable generators that supply fixed wiring systems must be grounded in accordance with 250.30 for separately derived systems if they supply a transfer switch that switches the neutral.

I am not using a transfer panel, I'm using an interlock directly back to the load center.

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Auger01

· #10 · Dec 6, 2012

Julius793 said:
Ok now that I got home.... To prove my point that the frame of the generator MUST be bonded to neutral look at 250.34

250.34 refers to the frame being connected to a grounding elecrode.

The way the op is connecting it, the generator frame is connected to the grounding electrode.

Care to try again? :whistling2:

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AdamBNYC

Discussion Starter · #11 · Dec 6, 2012

So while I dont think it will "kill" me if I dont disconnect the Neutral from the Generator, the NEC states that it could cause "Power Quality Problems"

So as long as there isnt anything wrong with disconnecting the neutral from the generator, it seems I might get cleaner power this way. Thats a big thing considering how dirty power from a generator could be.

stickboy1375

· #12 · Dec 6, 2012

AdamBNYC said:
So while I dont think it will "kill" me if I dont disconnect the Neutral from the Generator, the NEC states that it could cause "Power Quality Problems"

So as long as there isnt anything wrong with disconnecting the neutral from the generator, it seems I might get cleaner power this way. Thats a big thing considering how dirty power from a generator could be.

No, and not even sure how you came to that conclusion?

speedster1

· #13 · Dec 7, 2012

In leau of starting a seperate thread is there any issues with me using an interlock kit and backfeeding a 200 amp subpanel through a 30amp double pole breaker via an outside reliant box and 4 prong nema cord? I have an 8000w generac genset and my subpanel's neutral and ground are not bonded.

TTW

· #14 · Dec 7, 2012

speedster1 said:
In leau of starting a seperate thread is there any issues with me using an interlock kit and backfeeding a 200 amp subpanel through a 30amp double pole breaker via an outside reliant box and 4 prong nema cord? I have an 8000w generac genset and my subpanel's neutral and ground are not bonded.

An interlock is designed to prevent you from backfeeding your main panel, and possibly the transformer on the power pole, and zapping the lineman working to restore power.

Oh maybe I read it wrong. Wait, you have a 200 amp sub panel? What is your main service? That's one heck of a sub panel...

speedster1

· #15 · Dec 7, 2012

Well its actually my main circuit breaker but since I have a 200amp disconnect at my meter outside this box is technically considered a subpanel and the neutral and ground are unbonded.

I just wondered if floating the neutral came into play in my case since I'm backfeeding a breaker box with an unbonded neutral/ground

stickboy1375

· #16 · Dec 7, 2012

speedster1 said:
Well its actually my main circuit breaker but since I have a 200amp disconnect at my meter outside this box is technically considered a subpanel and the neutral and ground are unbonded.

I just wondered if floating the neutral came into play in my case since I'm backfeeding a breaker box with an unbonded neutral/ground

But they are still bonded back at the service disconnect...

This is just a random rant, not directed at anyone directly....

It's funny how people read a few threads on the internet, but really have no idea about grounding and bonding, personally, hire an electrician to do your generator. Some of these installations are just not DIY projects.

Billy_Bob

· #17 · Dec 7, 2012

stickboy1375 said:
...It's funny how people read a few threads on the internet, but really have no idea about grounding and bonding, personally, hire an electrician to do your generator. Some of these installations are just not DIY projects.

I agree. Of all things electrical, connecting a generator to a home's wiring is a *very* advanced electrical project!

Some of the issues surrounding this leave even seasoned electricians scratching their heads!

Part of the problem is with generators designed to be used as portable generators on a construction site which have integral GFCIs. There are all sorts of OSHA and other rules all about that which conflict with connection of a generator to a house.

And the ultimate mind boggler is a portable generator which will be used half and half - part time connected to a home's wiring and part time as a construction site portable generator.

Then to add to all this confusion, some generator manufacturers put out technical bulletins like the following, but other generator manufactures DO NOT!...
http://www.gen-tran.com/assets/pdfs/HondaGeneratorServiceBulletin20.pdf

Bottom line: Generators are not "plug and play"

speedster1

· #18 · Dec 7, 2012

stickboy1375 said:
But they are still bonded back at the service disconnect...

In my case considering the 200 amp breaker in the "subpanel" is in the off position the neutral connection back to the service disconnect is broken at that point. So I believe the only bonding at that point is at my generator.

I admit I'm not that knowledgable about electrical systems. I'm just trying to understand and learn some things.

Techy

· #19 · Dec 7, 2012

speedster1 said:
In my case considering the 200 amp breaker in the "subpanel" is in the off position the neutral connection back to the service disconnect is broken at that point. So I believe the only bonding at that point is at my generator.

I admit I'm not that knowledgable about electrical systems. I'm just trying to understand and learn some things.

Negative, main only opens the hot (ungrounded) conductors. Neutral(grounded) and ground are not broken.

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Billy_Bob

· #20 · Dec 7, 2012

speedster1 said:
...I admit I'm not that knowledgable about electrical systems. I'm just trying to understand and learn some things.

This is one of those things which has a *long* list of things to learn about! And when I make a list for something, like to go shopping, I always leave something off!

Anyway I will try to list the various issues / things to learn about...

First of all electrical codes/rules are not "wiring instructions to get it to work", rather many of those rules are for safety in case "something happens". An electrical malfunction, an unauthorized person is able to come along and flip a switch which causes a dangerous situation, future home owners might be placed in danger by plugging something in, etc.

And those rules have been created because of terrible things which have happened in the past. People have been electrocuted, homes have burned to the ground, etc.

So one thing to learn about is what all can go wrong...

-A wire becomes disconnected between the generator and the home's electric panel. What can happen if that wire is one of the hot wires? If a neutral wire? If a ground wire? (Or a combination of the above?)

If the neutral wire came loose between the house and the generator, is the generator wired to the house in a manner which could cause the metal frame of the generator to become energized? Perhaps a small child or animal touching the generator could become electrocuted?

-The power from the electric company goes out, you are not home. Other people in the house go to the electric panel and start flipping breakers / switches. Is there a possible way they could cause electricity from the generator to be sent out "backwards" on the electric company's lines? Might someone think a down power line near your house was not live, but in fact it is live (powered by your generator)?

-Ground loops and electrical "noise" caused by multiple grounds.

-Read about how a "main" electric panel has a neutral/ground bond, but a subpanel does not. Why is this?

-A generator with an integral GFCI and neutral/ground bonds on either side of that GFCI - The GFCI keeps tripping. Why is that?

-A generator can power 50 amps, then is connected to a house electric panel and in turn to a 75 amp load (things turned on in the house). How is the generator protected? Could someone other than you do this accidentally when you are not home?

-Could a generator be connected to a home's wiring system so that the 3rd grounding plug on outlets no longer functioned properly? Could this cause metal cases on appliances to become "hot" and electrocute someone touching them if there was a loose connection on one of the wires to the generator?

That is all I can think of. Basically overcurrent protection which protects the wires from becoming temperature hot and causing a fire. Protection from electrocution if any particular wire loses its connection or otherwise. Protection to keep the generator's electricity from going out on the electric company's power lines no matter who is flipping breakers or operating the generator. And problems with "ground loops".

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