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PTO Driven Generators
When you are figuring the needed capacity for a generator, the load capacity of the panel is not a good indication. 150 amps at 220 VAC for example is over 30 KW. It is highly improbable that you would need 30 KW for a typical household. You really need to figure the real usage and that takes some homework by adding up the power for each essential service.
In my experience a generator for a home that is 12KW or so would handle most households. Most can get by with less but some will need more. My backup generator is 7KW with 9KW peaks. By being careful, I have provided backup power for my house with a 2 KW generator.
You should not add the amperes from the two phases. When supplying power to your breaker panel, it is generally best to connect the 220 V line and balance the loads the best you can to minimize the current flow through the neutral conductor. For a 12 KW generator, that will amount to about 55 amps delivered at 220 VAC. You should only add amperes if you plan to supply all of the power with 110 VAC. This is not a particularly good idea, because the wiring in the alternator has to be sized for twice the current of the 220 volt generator for the same overall power.
But, let me back up for a second. If you needed 30KW for whatever reason, you will probably need a tractor of more than 50 HP to the PTO to produce that. You mentioned the Mid PTO, but most generators that I am familiar with operate on the rear PTO with a 540 RPM shaft. They use a gearbox or belt drive to increase shaft speed to reach an alternator speed of 3600 RPMs.
I tend to not want to use my tractor for power generation. The most likely time that I may need backup power is during some sort of storm. We don't have much snow where I live, but we do have flash flooding. Anyway, I think that I might not want to tie up my tractor for power when I may need to build a quick diversion dam or in other parts of the world, remove snow from my property.
My personal favorites are the Generac or other automatic units that connect to propane. If you lose power they kick on and switch over to supply power. When the power comes back on they shut off. I don't have one of these, but will in the near future. Since the power is interupted for a bit, sensitive electronics should be connected to APC or equivalent brands of UPS power supplies.
There is another thread on this subject that you may want to read.
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PTO Driven Generators
I agree that the service coming into your property can range from 100 to 200 amps or more. Most people do not size their backup generators to provide the full power that they might pull from the AC Line.
30 amps is only a ~7 KW generator. It only takes a motor of about 14 HP to drive this and even with the efficiency losses in a gear speed increaser it would take less than 30 HP. My 7KW/9KW peak generator has a Honda 18 HP gas motor and will deliver 30+ amps of 220.
I have not priced the Generac. If it is $10K then I am going to find something else. My current generator runs on gasoline and the maintenance issues that you mentioned originally do apply.
I was simply trying to put the whole picture in perspective for you. You might want your tractor with a FEL to move debris during one of the hurricanes that frequents your state. I have relatives in Tampa and around Tallahassee. They have different needs even being in the same state.
I like PTO generators in general, but I think that their best use is for power generation in remote areas, like construction sites, rather than for routine backup power at home.
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Tom, the best way to ground the generator is to run a ground back to the same single point ground for the electrical service. The transfer switch neutral should be connected there as well. If the panel is the primary panel, then the Neutral and Grounds will be bonded together in that panel. If the panel for the generator is not the main electrical panel, the ground and neutral are held separate and only connected together at the main panel. What I use for this is a 4 wire interconnect cord that has the ground. Some generators may not be set up for the four wire connection, but it is easy to adapt in a J box near the generator.
Doing otherwise may cause a phenominon called a ground loop. This is where there is current flowing through the ground wiring which results in a voltage potential. This is OK as long as all grounds are tied to a single point. If you have multiple grounds, currents can flow between the ground points and foul up electronics and other things.
It sounds like most of us agree that PTO generators may have a place, but not for routine backup power at your house. I have used one, but I don't own one.
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For a generator, the ground connection should be connected to the generator frame and the neutral should be floating at the generator. They should be bonded at the Service panel.
Additional intentional and unintentional grounds are common. If you set the generator on dirt, it may get some grounding through the frame as well as being grounded at the service panel. You might see the same thing happen when you connect some equipment with grounded frames to GFI outlets on long electrical runs. If the ground potential is different enough between the local ground and the conductor bonded to the service panel it may trip off.
Auxilliary grounds on remote buildings are fine. The problems happen if you bond all the grounds and all the neutrals together in all the panels. If you just run the two hot wires and the neutral to the remote panel, you should be OK. If you run a local ground, you will be OK. You MAY run into problems if you bond the ground and neutral together in that remote panel. There is no safety problem if the ground and neutral are not bonded together in the remote panel as long as they are bonded at the main Service Panel. (Ten volts of voltage difference between the neutral and ground is not hazardous to humans, but could generate large currents in a low resistance conductor.)
Where I have seen these separated grounds become a big problem is with computer network and cable TV wiring. I have seen sparks fly when an Ethernet cable from one building is connected to equipment in another building and the the coax is grounded on both ends. This is because of different ground potentials and huge currents can flow. You have to separate the grounds and isolate the equipment. This can be done with transformers or optoisolators.
So, what happens if you do bond the neutral and ground together in the remote panel? You may have current flowing in the ground and neutral wiring because of the different ground potentials. This current has the potential to set up some long term problems with respect to corrosion of the building elements and structure. The local ground rod itself could corrode due to anodic action. If that local ground fails, then anchor bolts in moist concrete that are tied to a grounded metal building frame may carry the current and start corroding. This may take years to develop and does not happen if the bonding only happens at the main service panel. No extreme safety issue with respect to electrical shock should exist as long as the ground/neutral bond is still good at the main service panel.
Codes vary and change. You need to do what is defined locally as the standard to keep your local authorities and insurance companies happy.
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Tom, a lot of what I was talking about relates to how the panels are supposed to be installed. From a practical standpoint, you have to ask a simple question...How often and how long am I going to be using the generator?
If you have a cabin and it is powered by the generator alone, then multiple grounding points are probably not going to apply. If you are using your generator for emergency power, then it is not going to be on for more than a few days at most, and is not going to cause the ground loop problems as long as it is completely removed from the electrical panel by the transfer switch when it is not being used. You may want to look for groundloops if you have problems with electronic equipment, but most of us are going to be more worried about refrigeration, heat, water pumping and so forth rather than computers and stereos.
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That kind of grounding extension is OK.
You should see what kind of grounding I do for my amateur radio towers. Each tower gets 9 to 12 eight foot ground rods. These rods are all buried below grade and the conductor connecting them is welded to each rod. But even these towers are tied to the single point ground at the incoming power service panel.
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