Question 46 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is C **Why option C ("permit momentary overloads") is correct:** Time-delay or delayed-action fuses are specifically designed to handle temporary, high-current surges—or momentary overloads—that occur when electrical equipment starts up. Motors (especially when starting), transformers, and certain control circuits often require a brief surge of current (inrush current) that is significantly higher than their normal running current. If a standard, fast-acting fuse were used in these situations, it would immediately blow due to the inrush current, even though the equipment is functioning normally. The delay mechanism within the fuse allows this temporary surge to pass without interrupting the circuit, yet it still provides protection against sustained, harmful overcurrents or short circuits. This characteristic prevents nuisance tripping while maintaining essential safety protection. **Why the other options are incorrect:** * **A) guard lighting and electronic circuits:** While fuses certainly protect these circuits, time-delay fuses are generally overkill for standard resistive lighting and delicate electronic circuits, which do not typically generate large, momentary inrush currents. Standard, fast-acting fuses are often preferred for these applications. * **B) prevent grounds in branch circuits:** Fuses and circuit breakers are designed to protect against **overcurrents** (which include short circuits and overloads). A fuse cannot prevent a ground fault from occurring; rather, it interrupts the current flow **after** a ground fault or short circuit causes an excessive current draw. Ground fault circuit interrupters (GFCIs) are the primary devices used specifically for ground fault protection. * **D) prevent opens in motor circuits:** Fuses protect against overcurrents, which, if left unchecked, would cause components to fail (open). They do not prevent the circuit from opening; their entire purpose is to safely **cause** an open (by blowing) when an unsafe current level is sustained, thereby preventing damage to the motor or wiring. Furthermore, time-delay fuses are used to *allow* the inrush current generated by a motor start, not to prevent the circuit from physically opening.