RoyJ wrote in
m:

I headed to the shop, pulled apart 3 motors:

-2hp cap start/cap run TEFC running on 240 volts: 189-227mfd/165 volts


Start windings on dual voltage rated motors are center tapped by the
jumpers so that the winding always sees the same (lower) voltage
regardless of which supply voltage it is connected for.


-1hp cap start compressor running on 120 volts: 534mfd/125 volts


Compressors are typically hard starting loads so it makes sense that the
motor is chosen to have high initial torque, and a high value capacitor.


-1hp cap start saw duty running on 120 volts: 216-259mfd/110 volts

Saws have very low starting torque requirements, seems reasonable to
have a smaller capacitor.



Now I'm really confused!

There's way too many motor construction and starting torque variables
for the 500uF/Hp rule of thumb to always fit.
Voltage ratings on the capacitors you listed are somewhat normal. The
start winding is so low duty cycle they use lower lated capacitors. Run
capacitors are usually 1.4 x rms voltage or peak ac voltage rated since
they are constantly in circuit.