While we were on this job running the 8/2 RX today, I copied everything I thought might be relevent.
From the air handler nameplte:
Volts 208/230
Motor HP 1/2
Motor FLA 4.3 Amps
From the stick on label supplied with the heat strip and placed on the nameplate of the AHU:
208Volts 230Volts
Heater Watts 3750 4600
Heater Amps 18 20
Minimum Circuit Ampacity 31.2 33.6
Maximum OCP 35 35
I don't know if this info will help or make things worse as far as figuring out the manufacturer's math, but its all we have to go by.
On a side note, it was cheaper to buy 125 foot roll of 8/2 for $129 than have them cut an 80 foot piece @ $1.72 per foot. The cost of wire has gotten ridiculous - it might as well be gas.