Will a 220V breaker trip at the designated current when only using
one leg? I thought that this was dangerous.

> You could repurpose your existing conductors as H-N-G. Feed with
> one side of the existing 30A breaker.
> Put in a subpanel with two 20A  breakers. You will have two 20A circuits,
> but you can't you them both to full capacity at the same time.

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