It struck me yesterday that I'd never bothered to find out how an electricity meter works. I'd guessed that there must be some electromagnet thing going on with the rotating disc. Perusal of the Internet suggests that the disc is part of an induction motor. The disc is non-magnetic but there are electric coils above and below it. These act as electromagnets. Because the supply is alternating, the strength of the magnetic flux through the coils, and thus through the disc, varies. The changing flux induces an emf in the disc which causes eddy currents to flow by Faraday's Law. By Lenz's Law the act as small electromagnets themselves which repel from the coil electromagnets, turning the disc. The bit I have not yet understood is the way that this is wired to make the speed of the disc proportional to the energy supplied. Oh, and I also need to look up 3-phase again. It's been nearly 3 decades since I had a working understanding.
