Effect of Bends
The effect of bends on pulling tension is substantial. In a system with multiple bends, the greatest tension will be developed through the last bend, as will the greatest sidewall pressure. If possible, the feed end of a cable should be close to the severe bends.
Inside Bending Radius
When calculating the sidewall bearing pressure (SWBP), use the inside radius of the conduit. The inside bending radius is the radius at the bend. Bends are categorized by the centerline bending radius. The inside bending radius (R.) can be obtained using:
- Ri = (RC - 0.5D)/12
- Ri = Inside bending radius (feet)
- Rc = Centerline radius of bend (inches)
- D = Duct diameter (inches)