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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.

Start of the feed from the main breaker box

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    When you say "tapped off" did you mean "taped off" the extra wires? Can you tell us exactly how that underground spice is connected? Please be careful, I would strongly suggest finding the breaker that feeds the line and shutting off the power before you attempt to document that splice. There are multiple considerations / possibilities here.
    – George Anderson
    Commented Jan 20, 2020 at 16:49
  • What type of cable is used for the 8/3 and the 12/2? Can you find which breaker controls this circuit and get back to me? Does the other end of the 12/2 measure 120V or 240V? What is this cable powering?
    – ThreePhaseEel
    Commented Jan 21, 2020 at 0:15
  • In fact, with the breaker off, can you post a photo of the inside of the electrical box?
    – ThreePhaseEel
    Commented Jan 21, 2020 at 0:16

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As a tap to a second building with no sub panel NO It would not be legal. The term tap usually means connecting a smaller conductor to a larger feeder and there are some cases where a tap is legal but not here with the info provided.

Maybe it’s legal if this is spliced not tapped if the breaker feeding the 8-3 is 20 amp it probably is ok

(they may have run larger wire to reduce the voltage drop) If the breaker is any larger than 20 amp it is not legal any size breaker larger than 20 feeding this would need a sub panel at the shop/shed sized for 20 amp max because of the 12 awg.

Updated for OP update. First if “normal wire” like Romex from the splice it is not legal from the splice. prior to the splice a 15 amp breaker the ampacity is fine and the breaker could be larger, voltage drop is not a hard code issue it is a recommendation in the form of a fine print note not enforceable. My concern is the type of cable. Back to the home if UF it has 4 conductors but 1 is capped with a wire nut.

If it were me I would get some 8-3 with ground UF and a proper inground splice kit. Extend the feeder to the shed and terminate in a minimum of a 50 amp main breaker sub panel. Drive a new ground rod and connect it to the sub. Upgrade the 15 amp single pole to a 40 amp double pole. Used the capped wire and the wire on the 15 amp breaker in the main panel to feed your sub panel. You asked if the “taped” connection was legal, I would guess it is not because it would need a listed in ground splice kit, these are fairly simple some have 4 butt connectors with an insulator that shrink tubing with an adhesive sealant (very inexpensive. Others are higher in cost where the splices are staggered with butt splices and each connection is sealed with shrink tubing with the adhesive sealant , the last type is the most expensive but the splices are made a plastic structure goes around the cable and epoxy is mixed and filled into the plastic and let dry (most expensive) I use all 3 types and in your case if the box is not always under water go with the least expensive and it will be fine.

So upsize the splice, add your new panel and new ground rod and you will have a nice service, 8 awg wire 125’ is 2.88% voltage drop at 40 amps so you don’t even have to worry about voltage drop.

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  • Would the buried electrical box have to be accessible?+
    – JACK
    Commented Jan 20, 2020 at 15:09
  • Splices underground do not always require a box but the op said there was one in this case.
    – Ed Beal
    Commented Jan 20, 2020 at 15:29
  • Apparently I was a little tired when I wrote this the wires are taped together in a splice. Additionally, the breaker is a 15 amp so the shop has minimal power amps.
    – Roberts2600
    Commented Feb 5, 2020 at 20:33
  • It happens, I updated my answer, it won’t be hard or very expensive to provide a 40 amp feeder to a 50 amp or larger main breaker panel, make sure to isolate the neutral from the ground buss or do not install the ground screw in most panels.
    – Ed Beal
    Commented Feb 5, 2020 at 21:50
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    No a splice in the pipe would not be code compliant. Actually after several years almost every under ground conduit run will have water in it. Code defines underground conduit a wet location. Direct burial splices are not expensive a thermo-shrink UF splice kit 4 wire with the shrink tube is only 14$ at the orange big box store that will handle up to 4 #8 wires. Tyco has the same thing for 12$. Putting a splice in a pipe will subject it to possibly always being in water and will violate code. I have made many splices that are actually under water) with listed splice kits for submerged use.
    – Ed Beal
    Commented Feb 6, 2020 at 14:17

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