You just had your new home inspected, and the inspector found “reversed polarity” at several electrical outlets some amateur had added. You know you need to fix this, but what is that reversed polarity stuff?
Electricity flows through wires like water through a hose. Pressure pushes water through a hose; energy pushes electricity through a wire. Each fixture must have an “electricity in” (hot wire) and an “electricity out” (neutral wire).
For safety reasons, the hot and neutral wires should never be reversed – if they are, that’s reversed polarity. A modern lamp has a plug with one wide and one narrow blade so it can only be plugged into the outlet one way. This ensures proper polarity.
Suppose you plug a lamp into an outlet with reversed polarity. Electricity enters from the metal ring around the bulb. The switch is then on the neutral line. When the lamp is turned off, the metal ring around the bulb is still electrified. If you touch the ring, you could get a shock.
Why? Even with the power switch off, you can still get a shock from the ring around the bulb because you are switching the neutral line, not the power line.