What is the purpose of grounding electrical equipment?

Answer 1

It is a safety measure for devices that have a metal case where a failure in the device could cause the case to be connected to the hot side of the circuit. By grounding the case the breaker will trip instead of you getting a shock.

Answer 2

The groundING conductor is usually the safety ground which serves as an emergency current return path in the event of a circuit fault or overvoltage. Like the groundED conductor, it too is grounded at the service entrance, but is also connected to metal surfaces and parts along the circuit, groundING them. It conducts current only if the current "seeks" to return to the service entrance along a path other than the Neutral (like through your chest, should a Hot wire becomes loose and contact metal in the circuit that you may touch). Since the grounding conductor doesn't normally carry current, its cross-section is sometimes smaller than the groundED conductor's. The grounding conductor's insulation is green (no other conductors can have green insulation) though sometimes it is bare copper. Sometimes the steel metal conduit enclosing the Hot and Neutral acts as the grounding conductor.