Final answer:
In a 120V wiring system, a black wire usually represents a live/hot wire, which is the answer to the student's question. It is essential to check local color codes to ensure proper identification, as they can vary by region.
Step-by-step explanation:
In a 120V wiring system, the color of insulation is used to identify different types of wires, and these color codes can vary by region. However, in many areas, particularly in the United States, a black wire is commonly used to represent a live/hot wire. This is the wire that carries voltage and serves to operate the appliance it's connected to. Neutral wires are often white or grey, and ground wires are typically green, yellow, or a bare wire. It's essential to check local color codes to ensure accurate identification because the same color might be used differently in other parts of the world. For safety and functional purposes, a three-wire system connects through a three-prong plug, which can only be inserted in one way.