Question 30 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is A. ### Explanation for Option A (Motor Starting Circuits) Option A, **motor starting circuits**, is correct because electric motors require a very high initial surge of current—often six to ten times their normal running current (known as inrush current or locked-rotor current)—to overcome inertia and start spinning. This surge lasts for a short duration (a few cycles up to several seconds). Standard (fast-acting) fuses would immediately blow when subjected to this brief but intense starting current, preventing the motor from operating. Time-lag fuses (or dual-element fuses) are specifically designed to handle these operating characteristics. They contain two elements: a large time-delay element that tolerates temporary, harmless overloads (like motor starting surges) without opening, and a separate quick-acting element to protect against dangerous high-level short circuits. Therefore, they are essential for protecting and properly operating motor circuits. ### Explanation for Other Options **B) emergency lighting circuits:** Emergency lighting circuits require high reliability and are typically sized for continuous operation loads that do not involve significant inrush currents (unless they are feeding a large bank of HID or ballast-driven lights, but the primary characteristic is continuous load). Standard fuses are usually sufficient, and the complexity of time-lag fuses is not required for the normal operating characteristics of these steady-state loads. **C) main lighting circuits:** Main lighting circuits, especially those using modern LED or fluorescent loads (or older incandescent loads), do not exhibit the massive, sustained inrush current characteristic of motor starting. While there might be minor surges when ballasts/drivers are energized, these are minor compared to motor start-up, making standard fuses suitable. **D) general alarm circuits:** General alarm circuits typically involve very low-power, steady-state loads (like control panels, signaling devices, or relays). They do not require substantial starting current and are designed to be highly reliable. Standard fast-acting fuses are used to ensure rapid interruption in case of a fault, protecting the sensitive electronic components. Time-lag characteristics are unnecessary and potentially detrimental to the rapid protection required.