I see your point Craigpump. But, I've heard of abrasion problems with wire in the well when, over time, motor torque rubs the wire in a given location and eventually wears thru the insulation. Type TH insulation is the thinnest ( and cheapest) of all wire insulation types. So, if I can get a better quality wire insulation type for less money, that's the only reason I'd reinvent the wheel. I think what the pump cable suppliers offer is convenience. If I buy my own #8USE I will have to twist it together along 400 feet. Most pump installers don't want to bother with that to save $100 or less. I'm buying a lot of other wire for other parts of the project at the same time, here's a way to lower the project cost.
Reach- I read the section in the AIM manual on using two different wire sizes. They present that as a means of dealing with the problem of having existing wire from source to the well head that's now too small when you upsize the pump. By upsizing the new wire down the well you keep total circuit voltage drop from getting too low. But why do this in a new installation? Valveman suggested using a smaller wire into the hole to intentionally drop the voltage for a softer start. As a newbie I'm wary of that, because I wonder what the long term effects on the motor might be of always running with voltage drop toward the lower range of what is 'tolerable'. But, if supply is 240v, and the motor is rated at 230v, does it make sense to design the system to deliver 230 to the motor? This is new stuff for me-
With this line of reasoning, though, maybe I should downsize my wire a bit. I'm 750 feet from pump to power with a 1hp motor. #10 wire is good for 650 feet with 1hp according to the chart. #8 wire is good to 950 ft. If I use the #10, I'll drop voltage a bit. Not sure how much, I can calc that. But if it drops the voltage from 240 to 230, maybe that's better for the motor. Thoughts?