What factor multiplier is used to determine the maximum time-delay fuse size from full-load current?

What factor multiplier is used to determine the maximum time-delay fuse size from full-load current?

• A. 1.25
• B. 1.50
• C. 1.75
• D. 2.00

Answer: (C)

When sizing a time-delay fuse, you must account for the brief inrush or surge current that devices like motors can draw at startup. Time-delay fuses are designed to tolerate these short surges, so the fuse rating can be larger than the continuous full-load current without blowing during normal startup. The standard multiplier used to determine the maximum fuse size from full-load current is 1.75. This means the largest fuse you should use is 1.75 times the motor’s full-load current. For example, with a full-load current of 20 A, the maximum time-delay fuse size would be 35 A. Using a fuse rated higher than that could compromise protection, since it would not reliably interrupt faults at the expected levels.

When sizing a time-delay fuse, you must account for the brief inrush or surge current that devices like motors can draw at startup. Time-delay fuses are designed to tolerate these short surges, so the fuse rating can be larger than the continuous full-load current without blowing during normal startup. The standard multiplier used to determine the maximum fuse size from full-load current is 1.75. This means the largest fuse you should use is 1.75 times the motor’s full-load current. For example, with a full-load current of 20 A, the maximum time-delay fuse size would be 35 A. Using a fuse rated higher than that could compromise protection, since it would not reliably interrupt faults at the expected levels.