A copper rod 1/4 in. in diameter and 3-ft long runs between two bus bars, which are at 60°F. The surrounding air is at 60°F, and the convective heat-transfer coefficient is Btu/h ft² °F. Assuming the electrical resistivity of copper to be constant at 1.72 × 10^-6 ohm – cm, determine the maximum current the copper may carry if its temperature is to remain below 150°F.