How to Bend a Box Offset in Conduit

What a box offset is

When something sits square on the surface your conduit runs along, a single offset is not enough: the conduit has to climb over it and come back down to its line. A box offset does that with two offsets back to back, so four bends in all, with a level stretch across the top. It is the same shape as a 4-point saddle, and electricians use the names loosely.

Measure the box and pick the angle

• Rise: how far the conduit has to climb. Measure from the surface the conduit sits on to the top of the box, then add the clearance you want. Measuring bottom of conduit to bottom of conduit gives the same number.
• Width: the box measured along the run, face to face. The straight across the top has to be at least this long.
• Room: the length you have along the run for the whole bend.

Use 30° unless the room says otherwise. Go to 45° when the run is short, and to 22.5° when you have the length and want less shrink. Whatever you choose, all four bends use the same angle.

Marking and bending the four bends

1. Decide where bend 1 goes and mark it, measured from the end of the conduit. Measure every other mark from this one, in one direction.
2. Mark bend 2 one offset-length (rise × multiplier) beyond bend 1.
3. Mark bend 3 a box-width beyond bend 2, then bend 4 one more offset-length beyond bend 3.
4. Number the marks 1 to 4 and draw a pencil line along the top of the conduit through all of them. The line shows you the plane.
5. Bend 1 with the hook toward the end. Roll the conduit half a turn and make bend 2 the same way, to the same angle.
6. Turn the bender round so the hook faces away from the end. Bend 3 is made like bend 2, and bend 4 like bend 1 (half a turn from bend 3).
7. Hold the conduit against the box. The straight should clear it, with both slopes finishing at its edges.

A worked example

Shrink for a box offset is twice that of a single offset of the same rise. Conduit past bend 4 comes closer to the end by that amount, so cut longer, or measure any stub beyond the box with it in mind.

Field shortcuts and mistakes

• Dry-fit the first offset. After bends 1 and 2, hold the conduit against the box. If it is high or low, you have only spent two bends.
• Add a little to both numbers. A bit of clearance on the rise, and a bit extra on the width, keeps the conduit off the box’s corners.
• Do not use a box offset for a narrow obstruction. A pipe or a coupling needs a 3-point saddle, which takes three bends instead of four.
• Do not roll between bends 2 and 3. The conduit stays flat across the top. A half turn there throws bends 3 and 4 the wrong way.
• Check the legs. Before you install it, lay the finished conduit on the floor. The two ends should be in line and the top flat.