We just put in a new window and I need to re-route one of the wires for a receptacle. The house wiring is from like 1984, it's 12/2 with ground 600 volt, and I picked up some 12/2 with ground 600 volt today and it's smaller by a decent amount. Is the new wire just more efficient thats why it can be smaller? Is there any reason I can't splice the two together?

 

Different insulation on the wire, the copper is 12 ga, you're OK, be sure to use a accessible junction box for the splice

 

The best way to do is to add another rec on the other side of the window & then connect them together. This will serve as a juction box. I can explain it better over the phone if you want to pm your phone number.

 

OR, he could pm me, it's a local call and I could explain it. Check my signature for why.

~Dave