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.
Best Answer
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.