Final answer:
AC systems over 1000V must be grounded to prevent electric shocks from induced electromotive forces on equipment cases. Grounding keeps the voltage close to zero, minimizing the chance of leakage currents and shock hazards. The safety relevance of grounding is illustrated in multiple figures and safety sections like 23.8 'Electrical Safety: Systems and Devices'.
Step-by-step explanation:
Understanding Grounding in High Voltage AC Systems
AC (Alternating Current) systems that operate over 1000V and supply mobile or portable equipment are mandated to have a grounding mechanism. This requirement is critical for electrical safety to minimize the risks of electric shocks. In the scenarios provided, such as those illustrated in Figure 23.35 and Figure 23.33, AC currents can induce an electromotive force (emf) on the case of an appliance, which can lead to a hazardous voltage that could cause a shock to users. By grounding the case, the induced emf is maintained near zero, significantly lowering the risk of electric shock.
Furthermore, as exemplified in Figure 23.60, even when an appliance is grounded, a person can still be shocked. This is because the large short-circuit current can produce a noticeable voltage on the appliance's case due to the non-zero resistance of the earth or ground wire involved in the grounding system. Electrical safety systems and devices, including grounding, are thus used to prevent not only thermal hazards but also shock hazards due to leakage currents and short circuits, as discussed in section 23.8 'Electrical Safety: Systems and Devices'.
High-voltage transmission systems, like the one depicted in Figure 21.54, also utilize grounding for safety. They employ a series of resistances, such as ceramic insulators, to reduce the risk of current leakage and ensure safety for both the equipment and personnel.