Final answer:
Grounding in AC systems, as specified in NEC Sections 250.20 and 250.21, is essential for preventing electrical shock and thermal hazards. It involves a three-wire system (live, neutral, and ground), where the neutral wire and the case of an appliance are grounded, and the use of circuit breakers or fuses and potentially GFCIs to provide multiple layers of protection.
Step-by-step explanation:
Understanding Grounding in AC Systems
Grounding in AC systems is a critical safety feature that is comprehensively detailed in NEC Sections 250.20 and 250.21. The grounding requirements for an AC system aim to protect against electrical shock and thermal hazards. To illustrate the concept, consider a scenario wherein a short circuit to an appliance's grounded metal case occurs. If a person, having a resistance to earth of only 3.00 kΩ, touches the wet case, the grounding enables a path for the electric current to safely dissipate into the earth, which minimizes the risk of electric shock.
Modern wiring systems, specifically the three-wire system, incorporate several safety features: a live/hot wire, a neutral wire, and an earth/ground wire. The neutral wire is grounded at both the voltage source and the user location, ensuring it stays at zero volts and provides an alternate return path for the current. The case of the appliance is also grounded, thus maintaining it at zero volts to prevent electrical contact with the user. A circuit breaker or fuse is in series with the live wire to guard against current overloads and consequent thermal hazards.
Additionally, appliances are equipped with a protective case to prevent direct contact with live wires. For enhanced safety, a Ground Fault Circuit Interrupter (GFCI) is often used to detect and prevent current leakages that might lead to unintentional paths, reducing the risk of electric shock even further.
Electrical safety systems, such as circuit breakers, fuses, and GFCIs, are thus integral to the three-wire system's effectiveness in preventing both shock and thermal hazards. They provide a comprehensive approach to ensuring the safety of household and industrial electrical installations.