A polarized receptacle

Common Options

A polarized outlet has one slot that is longer than the other. This is to ensure that the plug is inserted so that hot current flows through black or red wires, and neutral current flows through white wires. Although not as safe as a grounded system, polarization is the next best thing.

A grounded receptacle

The grounding circuit must follow an unbroken path to the earth. A third, rounded prong on modern plugs fits into the round slot in the receptacle. This slot connects to a wire--or to metal conduit or sheathing--that leads without interruption to the neutral bus bar of the breaker box. The system ground wire then leads from the bus bar to the earth. Often a cold water pipe is used for grounding instead of a grounding rod, because it is connected to water supply pipes that go deep under the ground.