As you might recall, I'm running 10 can lights on the new circuit added to the new sub-panel. I was going to run one branch line from the panel to a 2-gang box, pigtail it there and run three 12-2's to the switches.

I was planning on using 12-2 for the main branch run but remembered I bought some 10-2 last year in preparation for this project.

Should I run the 10-2 (v. the 12-2) from the panel to the gang-box, or does it matter?

FYI: the county inspector is coming out on Monday...I'll let you know how I fare.

 

First, you need to phone your inspector and check. Although the National Electrical Code would have no problem with 10-gauge wire on that circuit, there are some cities that prohibit mixing wire gauges on one circuit (but these cities are not the norm).

So let's say you find there is no problem mixing wire gauges. Then you certainly can run the 10-gauge if you want. However, make sure you have the right size wire nuts. It sounds like you are going to connect one #10 with three #12s. Make sure the list on the side of the box of wire nuts allows that.

Is there any advantage to the #10? Probably not much, but I'd need to know the distances involved and typical amperage to judge. There would be a slightly less voltage loss in the wire with the #10, but it may not be very significant.

Good luck with the inspector.

P.S. You are making a very common mistake in terminology with the word "pigtail". A "pigtail" is a short (about 3 inches) section of wire used to connect a wire nut to a device. If you are just connecting wires together with a wire nut, then you are just connecting wires together with a wire nut -- you are not using a pigtail.