For a noncontinuous load of 27 kW on a 3-phase, 480-volt circuit, determine the minimum standard size circuit breaker required.

To determine the minimum standard size circuit breaker required for a noncontinuous load of 27 kW on a 3-phase, 480-volt circuit, you first need to calculate the full-load current (FLC). This is done using the formula for 3-phase power:

[

\text{Power (W)} = \sqrt{3} \times \text{Voltage (V)} \times \text{Current (A)}

]

Rearranging this to find the current gives:

[

\text{Current (A)} = \frac{\text{Power (W)}}{\sqrt{3} \times \text{Voltage (V)}}

]

Substituting the values:

[

\text{Current (A)} = \frac{27,000 , \text{W}}{\sqrt{3} \times 480 , \text{V}} \approx \frac{27,000}{830.3} \approx 32.5 , \text{A}

]

For noncontinuous loads, the NEC (National Electrical Code) allows you to size breakers at 125% of the calculated load current to ensure safety and account for potential inrush currents. Thus