Chapter 10 Raceway Systems 145 Copyright Goodheart-Willcox Co., Inc. PROCEDURE Back-to-Back Bend A back-to-back bend produces two 90° bends on a single length of conduit. After the bends are made, both ends of the conduit are pointing in the same direction. See Figure 10-6. 1. Create the first bend by following the stub bend procedure. Mark the distance from the outside of the first bend to the position where the outside of the second bend should be. In this example, the completed stubs should be 40″ apart. 2. Place the conduit into the bender so that the star point is aligned with the mark. 3. Create the second bend, moving the han- dle of the bender back toward the first stub. 4. Measure between the outsides of both bends to confirm the proper distance. If you need to cut the second stub to length, mark and cut the conduit at the desired height after making the second bend. This is much more accurate than trying to control the height prior to bending, as you would while making an initial stub bend. An important factor when bending conduit is shrink. Shrink is the amount of shortening in a length of conduit caused by adding one or more bends. See Figure 10-7. The amount of shrink is determined by the angle of the bends and the height of the obstruction. For example, if the obstruction is 8″ and the bend angle is 30°, the shrink will be 2″. With the same obstruction and with the angle at 45°, the shrink is 3″. Most conduit benders have an offset bend chart on their handles listing the shrink at var- ious angles and obstruction heights as well as the horizontal distance between each pair of offset bends. See Figure 10-8. Otherwise, you can calculate all of these dimensions, using any angle and obstruction, with an online cal- culator or an app on a smartphone. Goodheart-Willcox Publisher Figure 10-5. Make a stub bend with a conduit bender and check it with a torpedo level. Making a Stub Bend Step 1. Subtract the bend radius from the height and mark the conduit at this value. Step 2. Align the mark with the arrow on the bender. Step 3. Bend the conduit. Step 4. Stop bending when the conduit reaches 90°.