A motor with a nameplate rating of 208V, 3-phase, 15 HP, 42 Amps, and a 1.15 Service Factor requires new overloads. What should the rating be?

To determine the appropriate overload rating for the motor described, we need to consider the full-load current and the service factor specified on the nameplate.

The motor's nameplate indicates a full load current of 42 Amps. The service factor of 1.15 indicates that the motor can handle a 15% increase in current without overheating. To find the overload setting, we multiply the full-load current by the service factor:

42 Amps × 1.15 = 48.3 Amps

However, this result gives us the maximum continuous current that the motor can handle under normal operating conditions. Overload relays should be set higher than the maximum continuous current to account for temporary overload situations.

In practice, overload settings may be chosen to accommodate additional factors like inrush current and other operational characteristics. Thus, considering these factors and industry standards, the overload rating is typically rounded up to ensure reliable performance without nuisance tripping.

In this case, the choice of 58.8 Amps represents a more conservative, practical rating that ensures the motor can handle startup currents and occasional overloads while protecting the motor from damage. This approach aligns with safe operational practices in electrical system design and maintenance.

Therefore, the reasoning behind selecting an