# Why can't we have superconductors?

My book says, "Short circuiting occurs when the live wire comes in direct contact with the neutral wire, so a zero resistance path is provided to the current. A heavy current then passes through the live wire of the circuit. "

Here in the book it is telling about zero resistance that means that the live wire will act like superconductor... so why can't we make superconductors by bringing live wire in direct contact with neutral wire?

Whether a material is superconductive or not is a property of that material, not of what we connect it to (although I believe that real superconductors have limits on current density before they lose their superconductive properties).

A piece of copper doesn't become a superconductor when connected between hot and neutral of a mains circuit. It will still have a finite conductivity of a little bit less than $$6\times 10^7\ {\rm S/m}$$ at ordinary operating temperatures, changing depending on the wire's temperature, how it was annealed and worked in drawing, etc.

When your book says the wire provides a "zero resistance path", what they really mean is a path with much lower resistance than the usual paths through the circuit. If the usual load on the circuit is 100 ohms, this might mean a 1 ohm path. If the usual load on the circuit is 1 ohm, it might mean a 1 milliohm path.

In general in circuit theory when we talk about "zero resistance" wires we really mean a resistance much lower than any of the elements that we've included in our model, not an actual superconductor. This makes it much easier to analyze circuits, while introducing errors that can easily be much smaller than the errors from our imperfect knowledge of the characteristics of the other elements we might use to physically build our circuit.

That junction, too, has a very small but finite resistance. Unlike superconductors, it won't be able to expel all magnetic fields.

Also, how do you use a single junction as a conductor? When you add lots of junctions to make your "superconductor", it will act like a metal wire and will have some resistance.

The title of the question is wrong. We are using superconductors for example in the LHC for the magnets that keep the particles on the desired path.

When you book speaks of "zero resistance" it is simplifying things. There will be a nonzero resistance, but it is much much smaller than the "usual" resistance the power grid might see for any device that might be connected to it.