why is it that sometimes you can get stray voltages on grounded metal parts of an electrical systems?

Question

and why doesnt it trip the breaker? does it have something to do with back emf?

Answer 1

Stray voltages/currents between grounded metal parts is caused by a difference in resistivity. Usually, it is because the ground rod has a greater resistivity than the metal parts connected to the water/drainage/gas system.
Again as has been said on other occasions in this forum, Ohm's Law comes into play..... Current is equal to voltage divided by resistance. So if there is a differing resistance between the two systems AND there is a low resistance path betweeen the electrical wiring and earth on an appliance, current will flow (continuously) to the frame of the appliance and to ground. So if current is flowing to ground and the appliance ground has a higher resistance to earth than the ground of the adjacent metal parts there will be a difference in potential between the two. This is often felt as a tingling sensation --- The reason why it doesn't trip the breaker is that the current flow is lower than the trip setting of the ELCB (earth leakage circuit breaker). It does not have anything to do with "Back EMF" back EMF is the voltage generated in a dc motor that limits the amount of current that can pass through the armature windings.......

If you have this problem, GET AN AUTHORIZED ELECTRICIAN TO INVESTIGATE AND CORRECT THE PROBLEM IMMEDIATELY. It certainly is a dangerous situation that can cause death.

Source: Electrical Engineer (ret) with 45+ yrs experience.