Chapter 10 Raceway Systems 141 Copyright Goodheart-Willcox Co., Inc. PROCEDURE Back-to-Back Bend B e A back-to-back ba bend produces two o 9 90 d ° bends on a single gl e length of conduit. Afte ft er the bends are made, a de both ends of the cond n du it are pointing in the he same direction. See Figure i g 10-6. 1. 1 Create the first bend d by following the stub bend procedure. d Mark the distance from the outside de of the first bend to the position n where the outside of the e second be b en d should be. In this exam a mp mp le, the com mp leted stubs should be 40″0 40 ″ apartr t. 2. Pla l ac e the conduit into the bend b en de r so that the star point is aligned w wi th th the mark. 3. 3 Create the second bend, nd , m mo ving the han- dle of the bender back ba ck toward the first stub. 4. Measure between w ee n the outsides of both bends to confirm on fi the proper distance. ce If you need ee d d t to cut the second stub b to t length, h m ma rk and cut the conduit u it at the desired si re d height after making the th second bend. be nd This is much more accurate ac than trying tr to control the height e ig prior to bending, as you would ul d 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 7 7 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°.