Bonded or Floating Neutral for generator?

[stumblinhorse]

Since my other thread got off the rails I will start a new one about Bonded or Floating neutral generators. I have ordered a generator/inverter for my house. I have a simple sub panel with a manual transfer switch/lockout. So I assume that I have to have a floating neutral generator to plug into my plug? Since the neutral will be in the sub panel tied to the same bus as the ground.

Anyone have experience with the simple lockout switch hook up and either blowing the GFCI breakers because of the neutral or not?

Thanks!

 

[ponytug]

I'm not an electrician.

You might want to browse this article;

Grounding A Generator - Requirements As Per OSHA & NEC

Grounding a Generator - The guide will clear your doubts about portable generator grounding as per OSHA, NEC for neutal floating & bonded sets.

yourpowerguide.com

One of the big issues is how your transfer switch to generator operates. Some switch the neutral, and some don't. Check.

Generator Grounding and Bonding Essentials

www.ecmag.com

Notice that the NEC is apparently silent on whether the generator has to have its own ground.

As far as I can tell, there are multiple viewpoints, OSH, NEC, generator manufacturers...

My take on this can of worms is...to be careful. I am not a code expert, but in my reading about the NEC take on this, they seem to be concerned about having two paths for the neutral current to flow on, one path on the neutral wire and one on the ground wire. If the main ground floats, then there can be significant voltages on the ground wire, and anything attached to ground, like conduits, stove frames, dryers, etc.

Many generators are shipped with the neutral bonded at the generator, assuming that the generator will be used as a stand-alone power source, with its own ground rod. You have to check. Mine weren't.

My takeaway is that if your neutrals are, and remain, connected and bonded to ground at the main service panel, having a single bonding point at the service panel makes sense to me. If that fails, then you run the very really risk of metal items in the house, stoves, dryers, conduit having significant voltages with respect to ground. Potentially lethal voltages. Putting the ground bond at the generator works as well. Having both the generator ground and neutral bonded, and the panel ground and neutral bonded, runs the risk voltage on the ground wire or shields between the two, and a ground loop between the two grounds (corrosion/interference issue). For short term, portable generator usage, probably not a major issue, but I'm not an expert!

Good luck, and this is definitely not expert advice.

Peter

 

[MAX-24-Dean]

Portable generators are shipped with the neutral bonded to ground on the generator frame. For stand alone generators (not supplying power to a building) driving a ground rod or connecting to a grounding system is a best practice. On most jobsites it was required by the AHJ to drive a ground rod.

When connecting a generator to provide power to a structure that has an electrical panel, the bond (neutral connection to ground) at the generator needs be removed.
The grounding system at the structure then provides the path to ground. There must be only one point in an electrical system that the neutral and ground are bonded together, inside the main electrical service panel.

 

[stumblinhorse]

My set up is that my outside main cutoff panel has a grounding rod then that 200 amp circuit is brought to the indoor panel. that has most breakers for the house, the. there is sub panel that has the generator lockout switch/transfer and the essential house circuits. So it has well, heat, fridge etc. When bypassing the main outside panel there is not a grounding rod involved in the connection from generator to that sub panel.

So bonded or floating is needed? The generator comes bonded and is simple to float.

Thanks again.

 

[MAX-24-Dean]

My set up is that my outside main cutoff panel has a grounding rod then that 200 amp circuit is brought to the indoor panel. that has most breakers for the house, the. there is sub panel that has the generator lockout switch/transfer and the essential house circuits. So it has well, heat, fridge etc. When bypassing the main outside panel there is not a grounding rod involved in the connection from generator to that sub panel.

So bonded or floating is needed? The generator comes bonded and is simple to float.

Thanks again.

All ground conductors entering a structure from a second source must be bonded to the system ground of that structure. Hopefully you have a ground wire going from the 200 amp panel to the sub panel. you would connect the generator ground to the system ground at the sub panel.
The net effect is that anything that would become accidentally energized at the structure has a ground path to trip a breaker.

 

[stumblinhorse]

All ground conductors entering a structure from a second source must be bonded to the system ground of that structure. Hopefully you have a ground wire going from the 200 amp panel to the sub panel. you would connect the generator ground to the system ground at the sub panel.
The net effect is that anything that would become accidentally energized at the structure has a ground path to trip a breaker.

Yes, there is a ground running from the outside panel to the main inside and then on to the sub panel.

So that means floating Is required?

 

[stumblinhorse]

So let me see if my pea sized brain can restate something that wasn’t obvious when I started this project.

In the sub panel there is a breaker/lockout/transfer switch that transfers power from the main panel “hot” wires only. The ground and neutral are not involved in that simple breaker. Therefore they still use the neutral and ground from the structure. Therefore neutral must be floating from the generator in order to not have more than 1 path to ground!

Correct maybe?

 

[MAX-24-Dean]

So let me see if my pea sized brain can restate something that wasn’t obvious when I started this project.

In the sub panel there is a breaker/lockout/transfer switch that transfers power from the main panel “hot” wires only. The ground and neutral are not involved in that simple breaker. Therefore they still use the neutral and ground from the structure. Therefore neutral must be floating from the generator in order to not have more than 1 path to ground!

Correct maybe?

Good reasoning there! Float the neutral as you concluded in your post.

On another note, if there is only one ground rod at the main panel you should drive another one at least 6 feet away from the first one to assure the resistance to ground is minimal. The ground wire from the panel should be one continuous conductor from the grounding bar in the panel to both ground rods.

Most electrical juristictions I have worked in require the two ground rods.

 

[PILOON]

My system is up and running for months now.
I never added a grounding and so far no problems with any electronics.

What came to mind.
When a 220 generator is wired with 4 conductors you have a ground (green) that does the job.
Mind U my genny is 9000watts.

Smaller generators (like 3-4000)very often only sport a 3 wire output evenwith220.

 

[etpm]

So let me see if my pea sized brain can restate something that wasn’t obvious when I started this project.

In the sub panel there is a breaker/lockout/transfer switch that transfers power from the main panel “hot” wires only. The ground and neutral are not involved in that simple breaker. Therefore they still use the neutral and ground from the structure. Therefore neutral must be floating from the generator in order to not have more than 1 path to ground!

Correct maybe?

I installed my own sub panel for my generator. When it was inspected the inspector was concerned that the neutral was floating in the sub panel. He asked me about it and I showed him how the sub panel neutral as well as the generator input neutral and ground went directly to the main panel. So the neutral was only tied to ground in the main panel. So you are correct. The inspector was very keen to see that there was only 1 path to ground. The inspector told me that is was quite common to see folks who did their own electrical work to not have floating neutrals and to have extra grounding points. He asked me about the floating neutral just to make sure I knew what I was doing.
Eric