Portable Generator, bonding neutral

billhartDecember 28, 2007

I just acquired a Coleman unit with Honda engine. I know, still junk without the Honda generator unit, but if I had it over the last 5 years, it would have only gotten intermittent use over 3 days one time and 1 day two other times, and maybe one use away from home.

The issue is that I was surprised to see it marked "Floating Neutral" and my meter confirms this. It isn't going to be wired into the house. I'm going to plan on using #12 and #14 extension cords through a window filler board.

I would think it should have the neutral bonded to ground. The instruction booklets that came with it make no mention of this subject, only of grounding the lug on the frame. I am considering opening up the box that contains the unit's outlets and adding a toggle switch between neutral and ground. Is this a good idea? Are there rules that require it to be a continuous wire rather than a switch? Or am I mistaken and it is ok as delivered?

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If the unit is going to be used as a stand alone unit it should have a bonded neutral and have a ground rod driven when in use.

If it will be used to power a panel the panel should have the bond and rods connected.
The biggest thing is to make sure there is only ONE ground-neutral bond.

    Bookmark   December 29, 2007 at 9:34AM
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Here is a PDF document about Neutral Bonding and Grounds for generators. The answer is it depends on how you use your generator and how you connect it up.

Best, Mike.

    Bookmark   December 29, 2007 at 10:31AM
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The article cited does not say much of anything about grounding generators, and does not even have a correct definition of common mode.
Common mode noise is present on BOTH the hot and neutral at the same time (it may also be present on ground).
The 'common' refers to the fact that both wires have a common signal.
If a 1000 V surge occurred on both hot and neutral at the same time it would be 'common mode'.
Unless a piece of equipment faulted to ground, nothing would actually happen.

Depending on how the neutral is treated a backup generator may be a separately derived source.
For large generators this is a common installation.
ALL connections to the grid are broken by the transfer switch.

    Bookmark   December 29, 2007 at 4:54PM
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Coleman 5500 watt unit has its panel marked "Neutral Floating" and the instructions say absolutely nothing about this topic.

This is a catch-22. Most people buying this size of unit will not be wiring them into a house panel, just using extension cords. The unit does not come set up for that. If you open it up and modify it, I'm sure all warranties are void.

What are people supposed to do?

    Bookmark   January 9, 2008 at 7:28PM
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"If you open it up and modify it, I'm sure all warranties are void."

Why are you "sure all warranties are void".

Having to change grounding and bonding is a pretty standard thing.
It varies with the final application and MUST be changed to comply with the NEC (or any local code).
Every small generator I have seen has hand a bonded neutral.
The fact that you may have one labeled "Neutral Floating"
means that the manufacturer has NOT bonded neutral and you may need to do this.

    Bookmark   January 10, 2008 at 8:53PM
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Funny, code in my state requires the alternate feeder box and breaker configuration have neutral and ground bonded. My new generator states that the generator must be grounded to a earth ground. I checked with a meter and the outlets on the generator are grounded to the generator frame.

The manual for the generator states the following,

" WARNING: Do not connect the generator output neutral to the frame or local ground. The generator ouput is isolated from ground. NEC and local codes require that the generator output remain isolated from local ground reference."

Looks like a contradiction.

Here is a link that might be useful: Photos of Gen Breakers

    Bookmark   September 26, 2010 at 4:49AM
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