Journeyman Electrician Practice Exam

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What is the minimum standard size of fuses permitted for overcurrent protection on a service disconnecting means in a small office building with combined loads of 28,400 VA?

  1. 100 amperes

  2. 125 amperes

  3. 150 amperes

  4. 200 amperes

The correct answer is: 150 amperes

To determine the minimum standard size of fuses for overcurrent protection on a service disconnecting means, it's essential to take into account the combined loads of the building, which in this case is 28,400 VA. First, we need to convert the volt-amperes (VA) to amperes, using the relationship that current (in amperes) is equal to the load (in VA) divided by the voltage (in volts). Assuming the building operates at a typical service voltage of 120/240 volts, the calculation would be as follows for a single-phase system: For 240V: Current (I) = Power (VA) / Voltage (V) I = 28,400 VA / 240 V I ≈ 118.33 A This result indicates that the minimum overcurrent protection must be greater than or equal to approximately 118.33 amperes to safely handle the load without tripping. In general, fuses come in standardized sizes, and the next standard size above 118.33 amperes would be 125 amperes. This signifies that choosing a fuse size of 125 amperes ensures reliable service disconnecting while allowing some margin above the calculated load. It is important to

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