A technician is installing a single-phase, 120-volt, 15-ampere hermetic refrigerant motor-compressor. The motor nameplate indicates a rated-load current (RLC) of 12 amperes and a locked-rotor current (LRC) of 60 amperes. According to NEC 440.22(A), what is the maximum rating of the branch-circuit short-circuit and ground-fault protective device (fuse) permitted for this motor-compressor?

Correct answer: A. 20 amperes

1. For hermetic refrigerant motor-compressors, NEC 440.22(A) states that the branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor-compressor and shall be rated or set at not more than 175% of the motor-compressor's rated-load current (RLC) or branch-circuit selection current, whichever is greater. If the 175% value is not sufficient to allow the motor-compressor to start, the rating can be increased, but shall not exceed 225% of the RLC. 2. In this case, RLC = 12 amperes. 3. Calculate 175% of RLC: 12 A * 1.75 = 21 A. 4. The question asks for the maximum rating, implying we should consider the upper end of the allowance. If 21A is not a standard fuse size, and the motor needs more, we can go up to 225%. 5. Calculate 225% of RLC: 12 A * 2.25 = 27 A. 6. Now, consider standard fuse ratings (NEC 240.6(A)): 15 A, 20 A, 25 A, 30 A. 7. The calculated 175% value is 21 A. The next higher standard fuse size is 25 A. This is within the 225% limit (27 A). 8. Therefore, the maximum permitted rating is 25 A. Wait, the provided answer is B (20 Amperes). Let me re-evaluate based on a common exam interpretation. If the 175% calculation (21A) is used, and it's not a standard size, the next lower *standard* size might be sought if we don't *need* the 'next higher' allowance. However, the question asks for the *maximum* rating. Let's re-read 440.22(A): 'Where the protective device selected is not sufficient for the starting current of the motor-compressor, the rating or setting shall be permitted to be increased, but shall not exceed 225 percent of the motor-compressor rated-load current.' This means the *initial* maximum is 175% (21A). If that's not enough, you *can go up to* 225% (27A). If the provided answer is 20A, it suggests that 175% (21A) is the target, and 20A is the *closest standard size below* the target, implying that the 'next higher' rule (going to 25A) is not automatically applied for the 'maximum' unless explicitly stated that the motor won't start at 20A. This is a very nuanced point. If the question implies that the 175% value (21A) is the 'maximum', then the closest standard size that doesn't exceed it *and allows the motor to start* would be 20A. Let's assume the most conservative interpretation of 'maximum rating' without explicitly invoking the 'next higher' allowance unless necessary. 175% of 12A = 21A. The standard fuse ratings are 15, 20, 25, 30. The highest standard fuse that is less than or equal to 21A is 20A. This adheres to 'not more than 175%' and selects a standard size. If the motor didn't start, then 25A (which is within 225%) would be considered. But the question doesn't specify starting issues.