Phases and circuit wire colors
This is what I know for sure: I don’t know much of anything yet. I was and am lost, but I will do my best to explain what I do know and how I figured out how to know the correct color of a circuit.
In commercial 120/208 volt electrical systems, there are three phases – A, B, and C. Each phase is one of three colors – black, red, or blue. Phase A is circuit 1 and 2 (black), Phase B is circuit 3 and 4 (red), Phase C is circuit 5 and 6 (blue). It then starts over with the phases. Phase A is circuit 7 and 8 (black) and on down the line. Phase A circuits are always black wire. Phase B circuits are always red wire. Phase C circuits are always blue wire. Seems easy enough to remember, right? Not for me, not until I learned the “rule of 6“.
Each multiple of 6 is always blue: 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, … are all blue circuits as are the numbers right before them: 5, 11, 17, 23, 29, 35, 41, 47, 53, 59, … It is not necessary to remember those odd numbers if you remember the multiples of 6. If you remember the color pattern black, red, blue, then you can figure out the other circuit colors by finding the closest multiple of 6 and backtracking.
For example, if you had to pull wire for circuit 21, you would find the closest multiple of 6, which is 24. Since 23 and 24 are both blue, it means that 21 and 22 are both red, so the color wire needed to install for circuit 21 is red.
I had to write out a cheat sheet chart for myself in the notebook I carry with me. It really helped me to visualize what a panel would look like. Hopefully some of this makes sense.
