Final answer:
The ground wire (or earth wire) must be grounded to be effective in a three-wire electrical system. Neutral and live/hot wires have specific roles and are configured to ensure safety through proper grounding and protection devices such as circuit breakers.
Step-by-step explanation:
When used in control cables, the ground wire (or earth wire) must be grounded in order to be effective. In the three-wire system, which includes live/hot, neutral, and ground wires, grounding is essential for safety and the proper function of the system. The earth/ground wire is connected to the case of the appliance and to the earth at both the voltage source and the user's location, forcing it to be at zero volts and providing a low-resistance path directly to the earth. This arrangement ensures that the ground wire is effective in preventing electrical shock hazards and allows the ground fault circuit interrupter (GFCI) to operate properly by quickly detecting any loss of current to unintentional paths.
Figure descriptions indicate that the neutral wire is also connected to the earth, forcing the neutral to be at zero volts relative to the earth, which makes it a safe path for current return. The live/hot wire supplies the voltage and current necessary to operate the appliance. To avoid electrical shock and thermal overload, a combination of grounding the neutral and the case and using a circuit breaker or fuse with the live/hot wire is used.