zxcvbob wrote:

Is this kosher with NEC?
Don't think so.

The suggestion I have seen is put a double pole double throw switch
on the H and N wires and switch them to a male socket to which you
attach an extension cord when necessary.

Any reason it needs to be that complicated? No need for a switch at
all, just put a regular plug on the wires going to the furnace and
move it to either a regular receptacle or an extension cords.



Use a single outlet, not a duplex. And a nice armored plug. Keep
everything short and neat.

Bob


And check local codes. It should be perfectly safe, but code is not
always logical, and just because it is safe does not mean it is legal.
That naturally doesn't stop a lot of people, but I like to keep things
up to code whenever possible, reduces the chance of liability.