So I know the formula for voltage drop [(Cable Length X Total Fixture Wattage X 2) / Cable Constant], however I have a question on the Cable Length portion. Let's say that I have a cable run that's 180' long. 100' into the main line run, I tee off 20' to one side to add 2 lights. 120' into the main line run, I tee off another 20' to one side adding a single light. What's my Cable Length? Is it 180' (the longest run), or is it 220' (the longest run plus the two 20' off-shoots from the main line)?
Thanks Steve, that's what I was thinking. Of course, I could always just run the run, and then use my DMM to check voltage at the end, but I come across this question mostly when sizing the wire. At the end of the day, it seems like it's always best to error on the side of caution in case the customer wants to expand some day anyway, meaning oversize the wire, and plan for the largest length. That way you have options down the road if they change their minds.
