Final answer:
A GFCI is required for new 120 VDC receptacle installations in kitchens and bathrooms, protecting against electric shocks by detecting and interrupting leakage currents.
Step-by-step explanation:
When installing a new 120 VDC receptacle, a ground fault circuit interrupter (GFCI) is required in areas where electricity may come into contact with water and pose a shock hazard, such as kitchens and bathrooms. The GFCI is a critical safety device that operates on the principle of electromagnetic induction. It constantly monitors the current in the live/hot and neutral wires, detecting any imbalance between them. A discrepancy indicates that some of the electricity is flowing along an unintended path, which can present a hazard. GFCIs are designed to trip and interrupt the circuit if the leakage current exceeds 5 milliamperes (mA), a threshold considered safe for humans.
The three-wire system, which includes the live/hot, neutral, and ground wires, has replaced the older two-wire system that lacked a ground wire. The presence of the ground wire in the three-wire system offers additional protection against hazards, notably if insulation on the live/hot wire wears out and contacts the case of an appliance. A GFCI installed in this modern wiring system further enhances safety by detecting leakage currents and tripping to prevent electric shock.
To summarize, GFCIs are essential in preventing shocks and are mandatory in areas with increased risk, like kitchens and bathrooms, where appliances may come into contact with water, substantially increasing the risk of electric shock.