I finally got around to adding a plugged connection to my furnace so that when the power goes out in the winter I can run it from my generator.
So I wire it up with what seemed a decent quality whip, make sure the polarity is right in the plug, and plug it all back in.
Turn the furnace on, and no good. The board's error code is saying reversed polarity. So I grab my meter and check the whip. Sure enough with ground on the bottom of the plug (because we're not in Canada

)the right prong is neutral and left prong is hot.
The plug prongs themselves were not polarized (no wide prong), but I still thought all plugs were set up the same. Guess not.
I had a few others in my parts bin, and every one I've checked has been right prong hot, but of course the one I grabbed was not.
Oh well, no harm no foul and I learned a lesson.