When sizing the motor-compressor branch-circuit protective device, the rating or setting shall not exceed 175% of the motor-rated load current or branch-circuit selection current. If protection is not sufficient for starting current, the rating may be increased but shall not exceed what percent?

When sizing the motor-compressor branch-circuit protective device, the rating or setting shall not exceed 175% of the motor-rated load current or branch-circuit selection current. If protection is not sufficient for starting current, the rating may be increased but shall not exceed what percent?

• A. 150%
• B. 225%
• C. 200%
• D. 250%

Answer: (B)

The key idea here is balancing motor starting inrush with protection. The protective device on a motor branch circuit is normally limited to 175% of the motor’s full-load current (or branch-circuit selection current) to avoid nuisance tripping during startup while still providing protection during overloads. If that protection isn’t enough to withstand the starting surge, you’re allowed to raise the rating, but only up to a specified upper limit. That upper limit is 225% of the motor’s full-load current. So the maximum you can set the protective device to, when needed for starting current, is 225%. Numbers below this (like 150% or 200%) would still be within the lower bounds or not reflect the maximum permissible increase, and going above 225% would exceed the allowed protection level.

The key idea here is balancing motor starting inrush with protection. The protective device on a motor branch circuit is normally limited to 175% of the motor’s full-load current (or branch-circuit selection current) to avoid nuisance tripping during startup while still providing protection during overloads. If that protection isn’t enough to withstand the starting surge, you’re allowed to raise the rating, but only up to a specified upper limit. That upper limit is 225% of the motor’s full-load current. So the maximum you can set the protective device to, when needed for starting current, is 225%. Numbers below this (like 150% or 200%) would still be within the lower bounds or not reflect the maximum permissible increase, and going above 225% would exceed the allowed protection level.