Bends Between Boxes
According to the NEC, no run of conduit between boxes is to have more than 360 degrees of turn in it, or four quarter bends. A conduit run with more then 360 degrees of turns in it must have an accessible box to allow wires to be pulled to that box, and then on to the next box in the run.
The bend radius of conduit benders are manufactured to meet NEC code for minimum conduit bend radii. A 1/2-inch conduit has a minimum bend radius of four inches, 3/4-inch conduit is 4 1/2 inches and 1-inch is 5 3/4 inches.
Flexible conduits such as flexible metal conduits and nonmetallic conduits have similar rules for minimum bend radii. Bends must be made so that the minimum radius rules are followed, ie, four inches for 1/2-inch conduit, 4 1/2-inches for 3/4-inch conduit, etc.
Large Size Conduit
NEC Table 34424 specifies minimum radius of conduit bends for conduit ranging in size from 1/2 inch up to six inches. Bends for conduit over 1 1/4 inches in diameter are difficult to make during installation and are commonly purchased as factory bends and assembled on site.
A 1 1/4-inch conduit has a minimum radius of 7 1/4 inches. The radii increase with each size up to 30 inches for six-inch conduit.