Ditto on the Variac. It is a sort of half transformer and one side passes right on through from the mains with no switch. We used to call them “student eliminators” (especially when the output went to alligator clips!). Put a DPDT on the input end and isolation transformer is even better. For those who have not worked with high currents or spread out projects, ground by definition carries no current. All the things that we call ground around the room are at different potentials due to resistance in the “ground” wires. In a big building, the return side of the AC power at one outlet might be served by a different circuit than another outlet in the room. The potential diff on the returns can be 20 volts and no shortage of current. Now, if you really want to a student eliminator, look at the constant power circuit used by bio students for electrophoresis. Contemplate the behavior of a power supply that delivers constant power. They have a lid with a switch for a reason.
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