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PTO Driven Generators
My 6.5kw peak Honda generator runs the house just fine during outages. It will run everything OK but just not at the same time. I may have to juggle loads during outages but that seems a reasonable thing to do. The advantages are that a small generator costs less and it's also much easier to transport if I need AC out in the bush.
I installed ours as part of putting in a new service and panel. I had to change the wiring on most of the branch circuits to a new panel so I went for a generator panel that operates as a sub-panel to the main service panel. They are a bit cheaper than transfer switches since the breakers are rated for the branch circuit rather than the full utility service. I would have gone for a transfer switch if I hadn't been installing a new panel. I think that the costs of transfer switches are subsidized in some areas to encourage people install proper generator backup systems.
In my case the house was on an old 60A service and the new service is 200A. I took a few circuits such as the dryer and outbuildings on the main panel, split some existing circuits in the house and virtually all the original house ends up on the generator panel and not much is on the main panel. It is handy to have some lighting on the main panel so I can tell when the power comes back on. Our generator system doesn't automatically switch on and off.
I never thought about it much but I wonder how grounding is handled in most transfer switches and if the backup generator is assumed to have a neutral bonded to ground?
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Thanks AC! The switches we're required to use here have 3-point main breakers so the service panel neutral would be disconnected from the panel when operating on generator. What I didn't know is if all transfer switches nowadays have 3-point disconnects. If so I don't know whether the transfer switch is bonded to the service panel so the generator would get its ground through the service panel ground bus or if the transfer switch has its own bonding to the service ground. My generator panel is bonded to the service panel through the ground bus so my generator would be grounded through the service ground. It uses 3-conductor plus ground line.
I was wondering how it would work with a 3-point transfer switch if the switch weren't bonded to ground in some way. I suppose the generator would have to have its own ground and then the generator neutral and ground should be bonded. I'm not certain the neutrals and grounds are bonded together on all generators but knowing for certain could be important for some hook ups. I think the neutral would float otherwise. The main point of all this is that people who install generator backups should understand grounding or have it done by an electrician.
The single-point grounding ideal is sort of ironic because almost be definition most people around can't have it. Codes require well casings, plumbing and metal septic system drains etc. to be connected to the panel ground bus. Any outbuildings that house livestock have to have supplemental grounds.
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AC: Thanks for the explanation. I never knew why sub-panels aren't bonded--just that it's one of the things inspectors always check. An inspector told me that the utility did some research and the even with proper installations, typical grounds start deteriorating after only five years in the soils around here.
I guess that a 3-point transfer switch breaks the neutral from the utility and makes it to the generator feed. The service ground is still on the panel side of the transfer switch so the generator neutral is connected to the service ground. My generator panel is a little different.
The important thing as I understand is to ensure that a generator has its neutral bonded to a good ground somewhere and ideally at only one point. A floating neutral can produce 120V of ground potential.
My generator does have a bonded neutral and ground as it has to for standalone operation. I connected the generator ground into the shed's supplemental ground and I leave it that way. I suppose that does give me two points of grounding and maybe some loss of efficiency through ground loops. However, then I'm sure the generator is always grounded when I use it as a standalone. Otherwise I'd have to make sure the feed line to the house was connected just for the ground connection.
I had a sideline sound and lighting buz for ten years and grounding can become a specialty all its own.
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That's how I reasoned it as well. I wonder if the reason our utility company research found that good grounds don't last very long around here is that most of us have to have multiple point grounding by code?
When I installed our new service and panel I used two grounding rods or plates as required by code (which is not multiple grounds since they are on the same unbroken service ground line). I did extend the ground line to run to the opposite corner of the house where the soil stays damper due to drainage. Soil near the meter is sandy, dry and poorly compacted. The inspector liked the idea. He also said that the other benefit I mentioned of reducing the risk of lightening jumps inside the house was a rumor he had heard. I guess he was saying that it doesn't work.
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