A 480-volt, 3-phase, 50-horsepower motor is served by a feeder. The motor has a nameplate full-load current (FLA) of 65 amperes. The overcurrent protective device for the motor branch-circuit short-circuit and ground-fault protection is a non-time-delay fuse. According to NEC Table 430.250 and 430.52(C)(1) Exception No. 2, what is the maximum rating of this fuse, assuming the next higher standard rating is not permitted to exceed 175%?

Correct answer: C. 110 amperes

1. First, find the FLA from NEC Table 430.250 for a 50HP, 480V, 3-phase motor, which is 65 amperes. (The nameplate FLA is only for overload protection, not short-circuit/ground-fault protection). 2. Next, apply the multiplier from NEC Table 430.52 for non-time-delay fuses, which is 300%. 3. Calculate: 65 A (Table FLA) * 300% = 195 A. 4. However, NEC 430.52(C)(1) Exception No. 2 allows for the next higher standard overcurrent device rating when the calculated value does not correspond to a standard rating, provided it does not exceed a maximum of 175% for non-time-delay fuses. This exception is for when the 300% value doesn't allow the motor to start. Let's recalculate using the 175% allowed in the exception boundary when the 300% is too high: If the motor cannot start with 300%, and the next higher standard rating is required, we must consider the 175% limit for non-time-delay fuses as a check. If 175% (65A * 1.75 = 113.75A) does not allow the motor to start, we can go up to 300%. This question implies we might need to go higher, but we must check the 175% first. The standard fuse ratings are 100A, 110A, 125A, 150A. If we use 65 A (Table FLA) * 175% = 113.75 A. The next standard fuse size above this is 125 A. But let's re-read the question carefully: 'assuming the next higher standard rating is not permitted to exceed 175%'. This phrasing strongly suggests that 175% is the *absolute maximum* permitted in this specific scenario, likely due to some unstated condition where the 300% is not allowed or is too high and 175% is the limit. So, 65 A (Table FLA) * 1.75 = 113.75 A. The maximum standard fuse rating *not exceeding* 113.75 A is 110 A. If the question meant 'if 175% is the maximum multiplier', then 110A is the answer. If it meant 'if 175% is the *next step* we can take before going to 300%', then 125A might be the answer. Given the wording 'not permitted to exceed 175%', it implies 175% is the upper bound for the selected fuse. Thus, 65 A * 1.75 = 113.75 A. The highest standard fuse rating that does not exceed 113.75 A is 110 A.