I just bought a house that has a 16x12 shed in the back, and I'm planning to use it as a small woodshop. I'm looking to install at least two 20-amp circuits in there. Currently, there's a 4-wire, 12-gauge feed coming from the main house supply with a 20-amp breaker. The setup has a red wire that's not connected, and I think it might not be hooked to anything in the junction box in my basement either. With all of this in mind, I'd like to know if I should just replace the existing breaker with a 20-amp double pole breaker and add a sub panel in the shed to support a second 20-amp circuit. While this sounds like a lot just for one additional circuit that may not be independent, I would prefer not to pull new wire as I'm unsure of the conduit size underground. I'm hoping to get some easy yet proper advice on what to do next. Thanks!
3 Answers
Another option would be to replace the 12/2 wire going from your main panel to the junction box with a 12/3, and put it on a two-pole breaker. You wouldn't need a subpanel for just one multi-wire branch circuit, but make sure there’s a disconnect for the shed to cut off all power. A double pole single throw switch could be the most affordable option for that.
To achieve your goal, you might want to consider installing a multi-wire branch circuit (MWBC). You could use a tandem breaker in your main panel which would allow both circuits to share a neutral since they’re out of phase. This setup would eliminate the need for a subpanel in the shed, making it a simpler solution.
Also, keep in mind that MWBC breakers need to be labeled correctly and should have a tie bar.
If you're thinking long-term, you might want to consider running a 6-gauge wire to a subpanel. It could seem excessive now, but you don't want to regret it later if you need more power.
Just make sure that the wiring used is suitable for outdoor environments. I've seen cases where standard Romex was replaced with higher gauge multistrand wire that has a waterproof rating. Look for wires labeled with a 'W' like THWN-2.