Stan, the way I was taught at NEC Seminars wayyyyyyyyyyy back when I practiced power distribution, was to:
1) Compute the "maximum continuous current"
2) Size the conductors to have a minimum ampacity of 125% of that
3) Provide Overcurrent Protection to protect the wire
4) Compute the line voltage drop (depends on current, wire and distance) and if its excessive upgrade the conductor size.
Voltage drop calculators are all over the net, all you need to know is the current, wire and distance EASY PEASEY
NOTE in a series circuit you can have different components or conductors etc drop voltage, and it makes no difference where they are in the circuit, first last or in the middle. The goal is to minimize wasted line voltage drop so the intended load gets as much as possible so you DO NOT have wasted I Squared R energy and heat losses in the line
If there are different size conductors in the line you would need to compute the voltage drop on each one. The bigger conductors have less per foot while the smaller conductors would have more. Compute each then add them all up piece of cake
Heres as an example ONLY, not the best not the worst, of an online Voltage Drop Calculator
John T Long retired and rusty EE so no warranty