HOLT Electricians Practice Exam

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What is the percentage limit for trip current of the next higher size overload relay for motors with a 1.12 service factor?

120 percent
125 percent
130 percent
135 percent

The correct answer is: 130 percent

The percentage limit for trip current of the next higher size overload relay for motors with a 1.12 service factor is set at 130 percent. This percentage is significant as it ensures that motors operating above their rated service factor can still have appropriate protection while preventing nuisance tripping during normal operation. The service factor is a safety margin that allows the motor to operate above its rated capacity, accommodating short-term overloads. A service factor of 1.12 means the motor can handle 12% more than its rated full-load current without overheating or damage during normal conditions. Thus, when considering the next higher size of an overload relay, it’s crucial to set the trip current to a level that reflects both this increased capacity and the need for protection against sustained overload conditions. In this context, the 130 percent specification allows the overload relay to trip at a level that corresponds with the motor's capability while also maintaining protection. Knowing this percentage aids electricians in selecting the right overload relay in compliance with National Electrical Manufacturer Association (NEMA) standards, ensuring efficiency and safety in motor applications.