Journeyman Electrician Practice Exam

The required ampacity percentage for the highest rated motor in a group of motors is 125%. This requirement ensures that the branch-circuit conductors are adequately rated to handle the starting and running currents of the motor, which can be significantly higher than their normal operating current. When motors start, they often draw a much larger current than during steady state operation, which is known as inrush current. The National Electrical Code (NEC) dictates that conductors supplying motor loads must be sized to handle this increased demand without overheating or tripping circuit protection devices too frequently. By using 125% of the highest rated motor's full load current, the conductor can safely accommodate both the inrush current at startup and the continuous running current. This practice helps in preventing potential damage to the wiring and ensures the reliability of the electrical system. Other percentages such as 100%, 150%, or 200% do not align with standard practices for sizing conductors for motor loads, as they either understate the capacity needed (100%) or are unnecessarily excessive (150% and 200%), which could lead to inefficient conductor usage and increased costs without significant benefit.