A mains tester works because the potential difference between the live and Earth makes a very small (imperceptible) current flow through the tester and our body to Earth. This current is just enough to light the lamp / Neon. When you stick it in the Neutral socket
, the potential difference (just a volt or two, usually) is not enough to give sufficient current to light the neon.When the tester light glows, it mean electrons flow like,from live terminal > tester > body > floor & walls of building > inside the earth>goes back to the generator, via earth or neutral
conductor (Please note that somewhere, Neutral
and Earth are connected together so we have, in effect, a huge loop of circuit.)
Above description is for AC supply only ( path complete thorough earth or nutral to generator neutral
), however please note the fhilosophy is not applicable for DC supply where - V is in floting condition (not grounded or earthed) so due to un completation of that circuit tester light will not glow.