I'm planning to replace my existing sub panel outside of the house and the wire. The main is in the laundry room and it will run into the attic and out to the opposite side of the house which already has a conduit installed. Reason why I'm replacing the wire because who ever the previous owner has installed the sub panel only use one wire to connect both terminal to power the sub panel.
My plan is to install a 60 amp panel, using 4 gauge (3 conductors with ground), but I'm not sure if I should use SER, NM-B, or start with NM-B then connect to THWN, or any other option? The wire will be 100ft run from the main to the sub panel.