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My current setup: Main panel has 60A 240 breaker that feeds Generator subpanel which has 10 circuits on it. The Gen Feed to the subpanel comes from buried 10-3 in my shed. That works well for running the generator. The subpanel has the metal slider to lockout Gen from Main feed.

Now I'm considering an electric mower, which would preferably be stored and charged in the shed, plus I wouldn't mind a light switch out there. So with the infrastructure of 10-3 underground, but with opposite polarity (i.e. generator input prongs) in the shed, is there a safe way to switch from "Generator feeding house" to "House feeding shed"? Obviously, or maybe not, I don't want to power the shed/mower with the generator.enter image description here

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  • How comfortable are you working in service panels? Can you shoot a pic of your main breaker panel? – Harper - Reinstate Monica Apr 12 '19 at 21:46
  • Can you post pictures of the panel? I take it the 10-3 is direct buried UF and not a conduit job, for that matter? – ThreePhaseEel Apr 12 '19 at 22:15
  • we meant your panel, including cables coming into it. – Harper - Reinstate Monica Apr 13 '19 at 5:28
  • electricgeneratorsdirect.com/products-image/360/3028_500a.jpg The website is being grumpy about uploads. That link shows my transfer switch. The 60A top left is fed by a 2 space 60A from the main panel, the 30A top right is fed by the buried 10-3, via a generator inlet on the side of the house. I'd love to figure out a couple of AC relays that would determine the logic of the 10-3 connection. Something like (if main=hot, then new 15A breaker feeds 10-3 to shed, else generator feeds panel). I haven't found the right relays to do that, and I don't know how to get that up to code... – idrivea911 Apr 13 '19 at 5:32
  • Got the photo to upload. Blue flex conduit at the bottom carries the 60A feed as well as all the returns back into the main panel. 10-3 generator feed is white coming from top of transfer switch. – idrivea911 Apr 13 '19 at 5:40
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You're just as well off trenching in a conduit

The rub with what you're describing is that you'd have to switch both ends of the feeder cable to make it work, with all the logic based on the presence of utility power at the main house end. As a result of the extra control wiring that would likely be needed to control the shed-end switching, you are just as well off trenching another feeder in between the house and shed as you are trying to rig up something.

However, there is a way to spare future-you more of this pain. Instead of trenching a cable in now, you can install a conduit for this new feeder, and generously size it (2" is not out of place). This means that there's room for more than a single feeder in the conduit; you can even move the generator feeder into the same conduit as the shed feeder once you have the conduit in place.

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  • After adding up the costs and code violations of my planned relays, I think you're right. Not sure if I'm committed to conduit as I'd be inclined to pull up the existing 10-3, but ill trench new power for sure. – idrivea911 Apr 16 '19 at 23:29
  • @idrivea911 -- even if you're pulling up the existing 10-3, conduit's a darn good idea anyway – ThreePhaseEel Apr 17 '19 at 0:30

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