Q: I am installing 500-metric-circular-mil-copper, 15-kilovolt cable with 133% insulation and a copper tape shield. The cable manufacturer gives a minimum bend radius of 12 times the cable diameter, which is 1.6 inches. Does that bend radius apply only when you are pulling cable around a 90o angle, and does it change when you are pulling cable around a smaller angle? If so, how do you calculate the change?
A: No, it does not change. The manufacturer states the smallest bend radius that you can use, regardless of the degree of the bend. Based on the cable manufacturer`s guidance, the minimum bend radius for your 1.6-inch-diameter cable would be 19.2 inches.
However, the 1996 National Electrical Code, Article 334-11, which covers the bend radius for metal-clad cable, states: "All bends shall be so made that the cable will not be damaged, and the radius of the curve of the inner edge of any bend shall not be less than shown below.
(a) Smooth sheath.
(1) Ten times the external diameter of the metallic sheath for cable not more than 3/4 inch (19 milllimeters) in external diameter;
(2) Twelve times the external diameter of the metallic sheath for cable more than 3/4 inch (19 mm) but not more than 11/2 inches (38 mm) in external diameter; and
(3) Fifteen times the external diameter of the metallic sheath for cable more than 11/2 inches (38 mm) in external diameter."
Based on Article 334-11, the minimum bend radius for your 1.6-inch- diameter cable would be 24 inches.