Perfect conductor
A perfect conductor or perfect electric conductor (PEC) is an idealized material exhibiting infinite electrical conductivity or, equivalently, zero resistivity (cf. perfect dielectric). While perfect electrical conductors do not exist in nature, the concept is a useful model when electrical resistance is negligible compared to other effects. One example is ideal magnetohydrodynamics, the study of perfectly conductive fluids. Another example is electrical circuit diagrams, which carry the implicit assumption that the wires connecting the components have no resistance. Yet another example is in computational electromagnetics, where PEC can be simulated faster, since the parts of equations that take  finite conductivity into account can be neglected. Properties of perfect conductors. Perfect conductors: Distinction between a perfect conductor and a superconductor. Superconductors, in addition to having no electrical resistance, exhibit quantum effects such as the Meissner effect and quantization of magnetic flux. In perfect conductors, the interior magnetic field must remain fixed but can have a zero "or" nonzero value. In real superconductors, all magnetic flux is expelled during the phase transition to superconductivity (the Meissner effect), and the magnetic field is "always" zero within the bulk of the superconductor. Mesoscopic scale. Non-super-conducting metal can produce persistent currents  when reduced to a size that is smaller than the electronic coherence length. This persistent currents has been demonstrated in noble metal rings of a few micrometers.