Hi, Steve. Actually, this is pretty simple. Since you can get to the wire, just measure it (the current carrying copper wire diameter). You will need a tool like micrometers, dial calipers or you can get a plate with very accurate holes that will tell you what gauge wire you have. I would have to check some books to see what the diameters are for 12 and 14 gauge and will try to do this is somebody else doesn't come up with the numbers. I know what the numbers are for steel wire and sheet, .109" and .083" respectively, but am not sure that these are the numbers for copper wire. Don't forget to shut off the power to the box when you open one to measure.