HOLT Electricians Practice Exam

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Which percentage of the highest rated motor full-load current must feeder conductors maintain for supplying several motors?

The correct answer is: 125

When designing electrical systems for multiple motors, it is crucial to account for the full-load current of the motors to ensure that the feeders can handle the maximum anticipated load. In this context, the feeder conductors must maintain a percentage of the highest rated motor's full-load current to safely supply power to various motors without overheating or failing. The National Electrical Code (NEC) specifies that feeder conductors for motor circuits should be sized at a minimum of 125% of the full-load current of the largest motor being supplied. This is to ensure there is adequate capacity to accommodate the starting current surge that motors experience when they first start up, which can be significantly higher than their running current. By sizing the feeders at 125%, the electrical system is better prepared to handle the load without risking overheating or tripping protection devices due to inrush currents associated with motor starts. Therefore, selecting 125% is not only a requirement but also a standard practice to ensure reliability and safety in electrical installations involving multiple motors.