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I looked but couldn't find this asked already. I found a sub panel in the crawl space of my home. It looks to supply an upstairs addition.
It has 2 different 14/2 cables going into it from the main panel, each on a 15 amp breaker. Inside the sub panel are a 15 and 20 amp breaker, with the 20 amp connected to 12/2 running up to the addition and 14/2 on the 15 amp. My best guess is this was done to get 20 amps up to the bathroom by "splitting" the current over the 2 lines supplying the sub panel.
Is this even legal? I could probably replace the existing 14/2 going into the sub panel with 12/2, but I'm not sure that is an acceptable solution.

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    Can you post a picture of the main panel and the subpanel? – manassehkatz May 2 at 15:01
  • #14 feeder should not be supplying a subpanel, since it's only good for 15A and that is pointless. It cannot power anything 20A. The usual purpose of using dual /2 is to bring up both legs of hot and also neutral, this is the wrong way to do that. If you replace it, use something like 10/3. The 10 solves the ampacity problem and the /3 solves the split-cables problem. – Harper May 2 at 15:02
  • In addition, most jurisdictions do not allow panels, sub or not, to be located in areas with restricted access like a crawl space. So you cannot legally do anything to that because it is an illegal installation to start with. – JRaef May 2 at 18:53
  • Can you post photos of the main panel and the subpanel? – ThreePhaseEel May 2 at 23:02
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Either it's 120V subpanel and he's plain paralleling... which is rather bad.

Or it's a 240V panel, and he's supplying hot/neutral/ground with one cable and the other hot with the other cable. That's a different kind of bad.

Both are unacceptable. You should replace both cables with a single /3 cable:

  • 4/3 Aluminum or 6/3 Copper if you want 60A in this subpanel
  • 8/3 Copper if you want 40A
  • 10/3 if you want 30A
  • 12/3 if you want 20A
  • 14/3 if you want 15A, but this is fairly pointless.

And, both hot wires need to land on a 2-pole breaker which has common trip, meaning both legs trip together, and, move either handle, the other goes too.

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Note that a duplex/tandem/twin/double-stuff has independent handles and must not be used, as it will create a dangerous situation if you do.

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