Final answer:
Metal enclosures for electrical components must be connected to the ground conductor, creating a safe path for electricity and preventing electrical hazards.
Step-by-step explanation:
Metal enclosures for switches or circuit breakers are designed to ensure safety by preventing electrical shock and fires. These enclosures should be connected to the ground conductor. This connection provides a low-resistance path directly to the earth, which is essential for safety.
As illustrated in the references, if the insulation of the live/hot wire becomes worn and contacts the metal case, the presence of a proper ground connection will cause the circuit breaker to trip. This immediately discontinues the electric current, prompting repair and preventing potential injury or damage. The ground conductor is typically represented by a green wire and is connected both at the power source and the user's location, forcing the metal case of the appliance to be at zero volts relative to the earth.
Therefore, the correct answer is (a) Ground.