Ampacity of Conductors in Auxiliary Gutters

The maximum ampere rating of a 4 in. x ½ in. copper busbar 4 ft long and installed in an auxiliary gutter is _____.

a) 500A
b) 750A
c) 1,500A
d) 2,000A

See answer and applicable Code reference

The correct answer is: d) 2,000A

Article 366 covers the use, installation, and construction requirements of auxiliary gutters and associated fittings. As noted in 366.23(A), "Where the number of current-carrying conductors contained in the sheet metal auxiliary gutter is 30 or less, the adjustment factors specified in 310.15(B)(3)(a) shall not apply. The current carried continuously in bare copper bars in sheet metal auxiliary gutters shall not exceed 1.55 amperes/mm² (1,000 amperes/in.²) of cross section of the conductor. For aluminum bars, the current carried continuously shall not exceed 1.09 amperes/mm² (700 amperes/in.²) of cross section of the conductor."

Therefore, the calculation is as follows:
1,000A/in.² x 2 in.² = 2,000A