We just got into a house and I believe the electrical is a mess. House is approximately 40 years old. We found an 8/3 buried wire that runs to a detached shop/shed and about 10 feet from the shed it transitions to 12/2 wire. The extra wire(s) are taped off in a buried electrical box. I am not sure at this time which breaker the 8/3 wire goes to as things are not labeled correctly in the panel. Can anyone tell me if this is legal? Should I change this and route this to a sub-panel and then go to a 20-amp breaker to feed the shed? Thoughts/Suggestions?
Updated: 2/5/2020 Corrected my spelling from Tapped to taped. The wire goes to a breaker on the main panel that is 15 amp. This feed of wire goes a long distance and I would guess over 125 feet minimum so there is likely voltage drop to consider. The 8/3 wire states "general uses" and is only 110V, not 240V. I suspect this is a normal burial wire. The extra wire that should be going to the other bus is wired to the ground so it is a hot, natural, and 2 grounds. At the other end in the ground, the extra ground is taped off and not being used. Once it spliced it looks like thy use 12/2 wire, non-burial wire, and ran it the last 14 feet. This wire feeds the shop with about 5 plugs and 2 separate light switches.