I am trying to wire 12 light post that are 120volts and 100watt bulbs. i plan to do two runs due to total liner feet 700. First run of 350 feet will have 6 light post with 10 gauge wire. Second run will have 6 light post with 10 gauge wire ran to the first 350 feet then 12 gauge to the next 350 feet. I doing the different wire size to voltage drop. I was wondering if this is right or do I have to go with 8 gauge then 12 gauge. Is the a formula to figure out voltage drop using diffent wire gauge?