For motors with a service factor of 1.10, the overload protection device must be sized at no more than what percentage of the motor nameplate ampere rating?

The correct percentage for sizing the overload protection device for motors with a service factor of 1.10 is 115% of the motor's nameplate ampere rating.

This service factor indicates that the motor can handle a temporary overload up to 10% above its rated capacity without sustaining damage. As a result, when sizing the overload protection, it's crucial to account for this capacity. The National Electrical Code (NEC) typically allows the overload protection to be set at a maximum of 115% of the motor nameplate rating for motors with a service factor. This threshold ensures the motor is adequately protected against overheating and potential damage by allowing for a slight margin for brief overload conditions but not so much that it risks failure during extended overload scenarios.

Choosing 100%, 110%, or 125% would not align with the NEC recommendations for a service factor of 1.10, as these percentages either do not allow for adequate overload capacity or exceed safe limits. Therefore, 115% provides the right balance for efficient operation and protection.