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-   -   Generator: Floating the neutral (http://www.diychatroom.com/f18/generator-floating-neutral-165734/)

AdamBNYC 12-06-2012 10:17 AM

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!

Billy_Bob 12-06-2012 11:12 AM

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 12-06-2012 11:38 AM

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

AllanJ 12-06-2012 12:51 PM

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 12-06-2012 03:35 PM

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!

Auger01 12-06-2012 04:35 PM

Quote:

Originally Posted by AdamBNYC (Post 1067478)
Does this sound correct so far?

Yes. That is the right way to do it.

Quote:

Originally Posted by AdamBNYC (Post 1067478)
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 (Post 1067478)
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.

Julius793 12-06-2012 05:32 PM

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 12-06-2012 05:34 PM

Quote:

Originally Posted by Julius793 (Post 1067684)
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.

AdamBNYC 12-06-2012 05:57 PM

Quote:

Originally Posted by Julius793 (Post 1067766)
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.

Auger01 12-06-2012 06:31 PM

Quote:

Originally Posted by Julius793 (Post 1067766)
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:

AdamBNYC 12-06-2012 06:40 PM

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 12-06-2012 06:44 PM

Quote:

Originally Posted by AdamBNYC (Post 1067816)
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 12-06-2012 09:36 PM

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 12-06-2012 09:51 PM

Quote:

Originally Posted by speedster1 (Post 1067988)
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 12-06-2012 09:59 PM

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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