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Author Topic: Generator bonding/grounding  (Read 160 times)

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Offline EV607797

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Generator bonding/grounding
« on: September 24, 2018, 12:17:34 AM »
I recently purchased a small generator and noticed in the documentation that it has a floating neutral output.  I verified this with the wiring diagram.  It is a very basic generator, not the inverter type.  The output is literally the two wires from the alternator field windings.  Why in the world would any manufacturer sell a generator like this?  If a fault occurred between the hot and ground, the generator's frame would become energized and the breaker would not trip with no point of reference.

Of course, it's my intention to correct this by bonding the neutral and ground pins for the receptacle on the unit.  It has no UL, CSA or ETL certifications, so I'm pretty sure I already know my answer.  Before I do this, I'd like some input from our folks here with electrical (specifically NEC) experience in case I'm overlooking something.
Ed Vaughn

(540) 623-7100 (V)  (540) 693-5800 (F)
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Offline silversam

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Re: Generator bonding/grounding
« Reply #1 on: September 24, 2018, 06:06:48 AM »
Ed -

First - If you're planning on using this to power your home (or at lest certain appliances at home) during a blackout , then you will need to shut down the main breaker on your panel - either by manually throwing the main or with a transfer switch - but I'm sure you knew that.

Second - If I recall correctly then many portable generators came wired like that - on the assumption that they were just to power hand tools at a job site or some equipment at a food cart or some stuff at an RV site. It was (I think) a design to prevent a short circuit in an appliance from energizing the frame of the generator.

Is there a ground screw on the chase of the unit that you can connect to a ground rod or the grounded neutral in the panel? That might quell your fears.

Forgive me, it's been a while.

Sam

Offline EV607797

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Re: Generator bonding/grounding
« Reply #2 on: September 24, 2018, 11:42:46 AM »
Oh yes, I've installed a lifetime supply of transfer switches, both manual and automatic.  That's not the case here.  I'm just in an apartment and want to run a cord inside to power the fridge, microwave, etc.  Nothing would be hard wired here.

Still, with the ground pin on the generator's receptacle effectively connected to nothing, it might as well just be a two-pronged one.  With neither end of the generator's windings grounded, neither conductor actually becomes the "Hot" one.  With no point of reference for the hot, a malfunctioning device won't trip the breaker.  Technically, nothing connected could become energized in the literal sense.  THAT'S why I'm here asking questions.

Do I just go with a totally floating output and forget about the ground altogether?  Maybe I'm creating more of a risk by creating a grounded system.  Am I putting too much thought into this?

Yes, the generator has an external grounding lug for connection to a building frame or ground rod, but that's never an acceptable means for grounding the center pin of a receptacle.  All of this bonding must be made at the source, whether it occurs at the commercial service <OR> the generator.  That's why I'm leaning toward performing this bonding myself in the generator wiring.
Ed Vaughn

(540) 623-7100 (V)  (540) 693-5800 (F)
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Online hbiss

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Re: Generator bonding/grounding
« Reply #3 on: September 24, 2018, 12:36:49 PM »
I recently purchased a small generator and noticed in the documentation that it has a floating neutral output.

Both ways (bonded and un-bonded) are quite common and it depends on what the manufacturer thinks you will use the generator for. If you use it to feed your house through a power inlet and interlock on your main breaker you don't want the neutral bonded to ground at the generator because it's already bonded at the panel. I would though expect the receptacle ground pins to be connected to the generator frame.

If the generator is going to be used as a standalone with extension cords then, yes you want the neutral/ground bond because not doing so will prevent GFIs that are required on job site power distribution from functioning. 

But other than that, what can happen? You have a floating system- ground pins on the receptacles go nowhere, neither side of the output connected to the frame.  If you have a fault from one side of the output (I won't say neutral because there is no such distinction) to the ground conductor in a extension cord or in a tool there is no shock hazard because there is no reference to any other conductive object on this planet.

So really, I wouldn't worry about it unless you are using it with GFIs.

-Hal
I gotta get out of this business...


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Offline EV607797

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Re: Generator bonding/grounding
« Reply #4 on: September 24, 2018, 09:39:44 PM »
That's the direction I'm starting to lean, Hal.  You're right.  With no point of reference from the windings to ground, nothing is really 'hot'.  I guess it's no different than using a battery-powered inverter.  It is a small generator, likely intended for jobsite use, so I'm going to leave it alone for now.
Ed Vaughn

(540) 623-7100 (V)  (540) 693-5800 (F)
EMVaughn3@Outlook.com

Online NFCphoneman

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Re: Generator bonding/grounding
« Reply #5 on: September 25, 2018, 07:57:54 AM »
Am I putting too much thought into this?

Yes, you are. You live in an apartment complex. Five minutes after you walk away, someone is going to still the generator.

Your Friend,
Larry