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Old 12-06-2012, 09:17 AM   #1
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Generator: Floating the neutral


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!
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Old 12-06-2012, 10:12 AM   #2
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Generator: Floating the neutral


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
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Old 12-06-2012, 10:38 AM   #3
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Generator: Floating the neutral


No you leave the generator exactly as it was manufactured hook it up when you need and go on with life.
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Old 12-06-2012, 11:51 AM   #4
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Generator: Floating the neutral


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.
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Old 12-06-2012, 02:35 PM   #5
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Generator: Floating the neutral


Quote:
Originally Posted by AllanJ
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!
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Old 12-06-2012, 03:35 PM   #6
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Generator: Floating the neutral


Quote:
Originally Posted by AdamBNYC View Post
Does this sound correct so far?
Yes. That is the right way to do it.

Quote:
Originally Posted by AdamBNYC View Post
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.

Quote:
Originally Posted by AdamBNYC View Post
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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Old 12-06-2012, 04:32 PM   #7
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Generator: Floating the neutral


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
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Old 12-06-2012, 04:34 PM   #8
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Generator: Floating the neutral


Quote:
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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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Last edited by stickboy1375; 12-06-2012 at 04:39 PM.
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Old 12-06-2012, 04:57 PM   #9
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Generator: Floating the neutral


Quote:
Originally Posted by Julius793 View Post
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.

Quote:
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.

Last edited by AdamBNYC; 12-06-2012 at 05:01 PM.
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Old 12-06-2012, 05:31 PM   #10
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Generator: Floating the neutral


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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?
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Old 12-06-2012, 05:40 PM   #11
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Generator: Floating the neutral


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.
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Old 12-06-2012, 05:44 PM   #12
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Generator: Floating the neutral


Quote:
Originally Posted by AdamBNYC View Post
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?
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Old 12-06-2012, 08:36 PM   #13
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Generator: Floating the neutral


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.
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Old 12-06-2012, 08:51 PM   #14
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Generator: Floating the neutral


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Originally Posted by speedster1 View Post
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...
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Old 12-06-2012, 08:59 PM   #15
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Generator: Floating the neutral


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
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