Generator: bonded neutral safety concerns


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Old 04-23-24, 10:35 AM
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Generator: bonded neutral safety concerns

Hello,

2 questions:

1. I am having trouble understanding the safety issue when using a generator that has a bonded Neutral and a transfer switch which does NOT switch the neutral when supplying temp power to a home. I understand this creates a parallel current path on the neutral and ground going back to the generator but what is the issue? My guess in the frame of the generator and the service panel would be carrying currently and somehow cause a concern?

2. Looking on Generac and Wen sites, it seems most of their small inverter generators have floating neutrals. Considering most of these would be used in remote locations I would think a floating neutral would be a safety risk in the typical application.

Thanks


 
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Old 04-23-24, 02:02 PM
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There are several schools of thought.

I rent generators. I have for over 35 years. They have GFI protected 120v receptacles.
There is a main breaker on the L14-30 four prong 120/240v receptacle.
They are all neutral bonded.
They all do double duty as standalone use and home use.
This IN MY OPINION is the safest way to handle my circumstances.

If your generator has a GFI main breaker.... you have no choice in opening the neutral bond or the breaker will trip.

Here is my thought on this.....
There are four wires connecting the generator to the panel.
Two hots a neutral and a ground.
For the most part.... the neutral and ground is connected at the main panel.
If you lift the neutral from ground at the generator.... you rely on frame ground from the main panel.

What happens if the generator neutral going to the panel opens ?
The generator frame is now hot as it is no longer connected to the generator neutral which is it's ground source. That certainly is not a good thing.
 
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Old 04-23-24, 02:27 PM
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Some utility-provided portable generator hookups solve the "parallel neutral" problem very simply by not connecting a ground wire. They aren't bound by the NEC so they can do it.
 
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Old 04-23-24, 07:07 PM
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>If your generator has a GFI main breaker.... you have no choice in opening the neutral bond or the breaker will trip.<
Maybe this is why these small inverter generators are using floating neutrals? They have a GFI main breaker which would trip when hooked up to say an RV? Hooking up to RV would be a common use case for them I imagine.


..
>What happens if the generator neutral going to the panel opens ?
The generator frame is now hot as it is no longer connected to the generator neutral which is it's ground source. That certainly is not a good thing.< Good point.
 

Last edited by bob_m; 04-23-24 at 07:08 PM. Reason: spelling fix
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Old 04-24-24, 04:31 AM
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PJmax, in post 2 are you describing a double failure? Could you provide a sketch of the 4 wire connection from generator to panel showing the failure or failures?
 
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Old 04-24-24, 05:37 AM
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[color=#222222]>PJmax, in post 2 are you describing a double failure? Could you provide a sketch of the 4 wire connection from generator to panel showing the failure or failures?> Black (Hot) makes it to a lightbulb inside your house.

Lightbulb >> Neutral makes it back to main panel and jumps to ground since they are bonded at the main panel.

Main panel >> ground makes it back to generator frame and stops since it is no longer bonded to neutral.



Result,

Now the Frame of the generator and the main panel would be hot?


 
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Old 04-24-24, 04:09 PM
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This is two diagrams..... with neutral bonded to ground and not.

The top diagram is the way most generators would come. Mine are wired this way.

The bottom diagram illustrates no neutral to ground bond.
The generator metal frame is getting its ground via the green wire from the panel.
If the neutral should fail.... maybe a bad connection in the plug.... the green now tries to carry the neutral which it cannot do so the metal frame is now hot.

I believe the top connection method is the most safest overall.
The problem with the lower diagram is not just that the frame can become hot but because of the way the house panel is wired.... the frame is now truly hot with respect to actual ground.
 
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Old 04-25-24, 02:18 PM
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Pete,

In your bottom diagram, I agree the frame of the generator is hot. But, and maybe even more important, is also the main panel and all metal throughout the house hot via the equipment ground? thanks
 
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Old 04-25-24, 02:20 PM
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It would create an imbalance in hot legs with the neutral carrying the balance.
 
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Old 04-26-24, 09:29 AM
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"It would create an imbalance in hot legs with the neutral carrying the balance."

Was that in response to my question about the main panel case being hot as well in your scenario #2 (bottom pic) above? Thanks
 
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Old 05-01-24, 06:54 AM
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What in the panel and generator are at earth ground?
 
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Old 05-01-24, 04:13 PM
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Not sure what you aren't following.

The panel is grounded thru ground rods, metal water service and neutral from service.
The generator itself is not connected directly to ground.
It gets grounded when it gets connected to the panel.

The inbalance is to the generator.
 
 

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