Can someone give me a formula or a reassuring statement regarding the facts on voltage drop, on a circuit that includes different sizes of wire. I'm on a job where the spec is anything over 250' on 277v branch circuits must be upsized from #10 to #8. The problem I'm running into is some say that you can pull the first 250' in #8's and the rest of the length in #10's. Or pull #8's to the last J-box if it's over 250' and then run a mc whip in #12's. Any comments would be appreciated thank you.