Bus Bar Ampacity

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Bus Bar Ampacity

The NEC stipulates in the article on auxiliary gutters that a copper bus bar has a continuous ampacity of 1000 amps per square inch. Aluminum is 700 amps per square inch.

So to calculate the ampacity of any bus bar, envision a cross section of the bar. Length is not a factor in the calculation.

Multiply the two dimensions of the cross section as measured in inches. The product of these two numbers is the cross sectional area.

Next multiply the area times either 1000 amps/sq inch of copper of 700 amps/sq inch if aluminum.

This calculation is a straight square inches of the bus bar times 1000 amps/sq. inch if copper and square inches times 700 amps/sq. inch if aluminum.

So if you have a bus bar that is 1/2 inch by 3/4 inches (regardless of length) then it is .5 times .75 equals .375 times 1000 equals 375 amps if copper and .375 times 700 equals 262.5 amps if aluminum.

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