A dedicated circuit feeds a light in a dwelling. The light is on all the time. What could be a possible reason for this fault?

A dedicated circuit feeds a light in a dwelling. The light is on all the time. What could be a possible reason for this fault?

• A. Bad breaker
• B. Defective switch
• C. Neutral connection came apart
• D. Bad light fixture

Answer: (B)

A light that stays on when it should be controlled by a switch points to the switch not interrupting the hot feed. If the switch is defective—such as contacts welded closed or internal shorting—the hot conductor stays connected to the fixture regardless of switch position. In a typical switched circuit, the switch is in series with the hot lead to the light; a stuck-closed switch keeps that path complete at all times, so the lamp remains energized. Neutral coming apart would usually open or misbehave the circuit rather than keep it energized, and a bad breaker isn’t tied to the switch position in a way that guarantees the light stays on. A bad light fixture could cause odd behavior, but a stuck switch is the most straightforward and common reason for the light to be permanently on.

A light that stays on when it should be controlled by a switch points to the switch not interrupting the hot feed. If the switch is defective—such as contacts welded closed or internal shorting—the hot conductor stays connected to the fixture regardless of switch position. In a typical switched circuit, the switch is in series with the hot lead to the light; a stuck-closed switch keeps that path complete at all times, so the lamp remains energized.

Neutral coming apart would usually open or misbehave the circuit rather than keep it energized, and a bad breaker isn’t tied to the switch position in a way that guarantees the light stays on. A bad light fixture could cause odd behavior, but a stuck switch is the most straightforward and common reason for the light to be permanently on.