What is the minimum standard size overcurrent protective device required for a 120/208-volt, 3-phase feeder supplying a continuous load of 37.5 kVA?

In electrical installations, it's crucial to determine the appropriate size of overcurrent protective devices to ensure safety and compliance with national electrical codes. For a continuous load, you need to apply certain rules regarding sizing.

First, calculate the load in amperes using the formula:

[

\text{Amperes} = \frac{\text{kVA} \times 1000}{\sqrt{3} \times \text{Volts}}

]

For a 120/208-volt, 3-phase feeder with a continuous load of 37.5 kVA, this is calculated as follows:

[

\text{Amperes} = \frac{37.5 , \text{kVA} \times 1000}{\sqrt{3} \times 208 , \text{V}} \approx 104.1 , A

]

Since this load is continuous, the National Electrical Code (NEC) requires that overcurrent devices must be sized to handle continuous loads at 125% of their maximum rating. Therefore, the appropriate size calculation is:

[

\text{Minimum Overcurrent Device Size} = 104.1 , A \times 1.25 \approx 130