I recently obtained my dads old place in Northeastern Arizona and since it sat for so long the generator was stolen and so was our water tank, and now I am in the process of replacing the large generator and I wanted to see how I can find out exactly how large of generator I will need. The generator he had was a 25kw 3 phase generator. The pump is a 10 HP that is fairly old and pumps 100 gallons minute. According to the Arizona Dept Water Resources my "Well Depth is 340ft, Water Level 250, and casing depth 200ft, and casing diameter is 8 inches. And I am completely off grid with no power. I guess I have a few questions.

What size generator do I need just for this pump?

How can tell what voltage it is, I see generators of this size for sale that vary on voltage i.e. 208 240 120. I have pictures of the electrical box and how it is wired but I dont understand what it means.. I have photos attached of the electrical box if that helps.

First figure out if that is a 3 phase motor on the pump. If it is 3 phase, the resistance should be the same between any of the 3 power wires going down-- ignoring a protective ground wire. I think the pictures show some 3 phase stuff, but wiring for 3 phase does not seem to be intact.

After you figure out if this is 3 phase, we will look at what voltage the motor is.

You will need an ohmmeter that can measure low ohms -- maybe less than an ohm with at least a couple significant digits of accuracy. A 4-lead ohmmeter is best at that job. It is made for low resistances. There will be some math, but we can help you with that. See table 25 of the Franklin AIM manual. But you will also have to account for wire resistance. I know how to figure that out for a 3 wire pump, but not for 3 phase. For 3 phase, I think you will need to know how big the wire is and how far the pump is set. Or maybe just assume the pump is at 320. Then with the wire size, we would know the wire resistance closely enough. With that and your reading, we know the winding resistance. And from that we can compare to the know resistances of a 10 HP 3 phase pump.

If it is not a 3 phase pump, there would have been a control box... which could have been stolen.

100 GPM is a lot. Are you farming with the water or just trying to fill a new storage tank fast? Because if you are filling a 2000 gallon tank, you might be better off to run a smaller pump longer.

There are also solar solutions.