Nontime-delay fuses with a rating of ___ A are the largest permitted to be installed in a disconnect switch for a motor.

Nontime-delay fuses with a rating of ___ A are the largest permitted to be installed in a disconnect switch for a motor.

• A. 25
• B. 40
• C. 50
• D. 45

Answer: (C)

When protecting a motor circuit, the protective device inside the disconnect must be sized so it can interrupt faults safely while matching the switch’s rating. For non-time-delay fuses used in a motor disconnect, there is a fixed limit: the fuse rating cannot exceed fifty amperes. This upper limit exists because the disconnect switch and its fuse block are designed to handle up to that size, and using larger fuses would require different protection arrangements. So, fifty amperes is the largest allowed rating for a non-time-delay fuse in a motor disconnect; the smaller ratings could be used for smaller motors or different coordination, but they’re not the maximum allowable.

When protecting a motor circuit, the protective device inside the disconnect must be sized so it can interrupt faults safely while matching the switch’s rating. For non-time-delay fuses used in a motor disconnect, there is a fixed limit: the fuse rating cannot exceed fifty amperes. This upper limit exists because the disconnect switch and its fuse block are designed to handle up to that size, and using larger fuses would require different protection arrangements. So, fifty amperes is the largest allowed rating for a non-time-delay fuse in a motor disconnect; the smaller ratings could be used for smaller motors or different coordination, but they’re not the maximum allowable.