If you look at an electrical panel, you will find the fuses or breakers in two vertical columns. Years ago, when people had fuse boxes, the fuses would be numbered 1, 2, 3, 4, etc. They also number the slots in breaker panels, but the numbering system is a bit different in that you have two breaker positions for each number. So, if you look at your breaker panel, you should see that there is both an upper and a lower position for #1, #2, #3, #4, etc.

The reason for having two breakers for every designated number is that it makes it easier to know whether you're connecting wires to the same, or different, voltage sources. I'll explain that in the next post...