Wow! Good job figuring the voltage loss for each individual branch. But I went back and read this thread and I still don't know what you are trying to fix? Did the first pump only last 6 months? Or are you just worried about the 5HP control box on a 2HP motor?
Those motors will work with plus or minus 10% of rated voltage. I think they will be fine from like 220V to 260V. Having a 16 volt loss doesn't seem that bad to me. It also depends on the incoming voltage. If it is coming in at 240V or more, losing 16 volts shouldn't be a problem. But if the incoming voltage is low, you can't afford much loss.
Also as the voltage gets lower the amperage will increase. If the voltage gets too low the overload in the motor will trip. If it not doing that I don't think you have a problem.
The well was installed brand new in March 2016.
The original Grundfos Pump died in July 2017.
The issue began with a continuously decreasing flow of water from the time it was installed until the pump finally died. There is 80 feet of water above the pump. When the new pump was installed in July 2017 they did not replace the original control box (2HP).
In October of 2017 (3 mos after new pump went in) the Pumptec began throwing the solid orange light every 5 to however many minutes. The well drillers said it was from high winds in our area. We began monitoring with a log how many times this happened until it wouldn't stay on at all. They came out in February (last month) and installed the 5HP control box to solve the problem. So far it stays running BUT the water yield has gone from 4.5 gpm to about 2.2 gpm since February (last month). It still has 80 feet of water above the pump that stays continuous according to the draw down gauge they installed.
SO, if the first pump went out in 18 months, and the new pump is already having yield issues (even with the 5HP box) my idea is that he may have wired my well to take a 1.5 HP pump. He did mention that size in the beginning of the project but we decided on a 2HP pump. When he installed the wire he told me he was putting in larger than necessary wire so I could upsize my pump in the future if I wanted to.
Before I meet with him regarding the oversized Control Box as a remedy - I decided to investigate per recommendations on this thread as to why the original pump died so soon. The engineering report is all I have to present him when we meet to discuss why the yield is lessening AGAIN. I am no expert but from research I have done I noted that all experts recommend a 3% line loss and a maximum 5% line loss.
My thinking is that if the experts want 3% and NEC wants 5% MAX then the calculations from the engineer showing a 4% drop from house to Motor should be optimal?
I hope all this makes sense - my brain HURTS!!! I just wanna bake cookies! LOL
Thanks for your reply, your information is invaluable!
PS: I looked in the Grundfos Manual for the wiring specs and according to Grundfos the maximum footage for #8 wire is 620 feet. So the #10 he spliced in there weirded me out. The chart shows #6 wire could go all the way to max depth of 970' which seems to be in agreement with the engineering guy.
Jane