You say this is happening with the pad plugged in but switched off? Assuming it's a real effect, I'd have to wonder if "Hot" and "Neutral" are incorrectly wired on the power outlet, or if the switch for the pad is switching "Neutral" rather than "Hot" as it should.
If you are comfortable...
I need help designing some build-from-scratch DC motors. I'm looking to build really robust motors that I can be be sure will demonstrate clearly the principles involved, but that can be modified by my boys and that they can really *play* with and use to run simple toys. I've already shown...