For the question What makes Cooper pairs of electrons so fit for an unhindered current through a superconducting wire? where was a nice comment from CountTo10:
Assume any photons are effectively massive inside the superconductor, (through symmetry breaking), also assume that as one electron gets held back in the metal lattice, the other one of the pair gets pulled forward. They do not posses enough energy to produce retarding photons, so they meet no resistance.
Not getting response to this question of mine Why don't superconducting coils radiate? I'm asking this in an other way:
It is common sense that in a superconducting coil an electric current is flowing. Since the involved electrons are moving in circles they are subject to an acceleration. Do this electrons emit EM radiation?