12" conduit offset: marks and shrink at every angle

Choosing an angle for a 12" offset

A 12" offset is a big move: around a duct, a beam or another run of conduit. At this height the question is length. The bends span 24" at 30° and 17" at 45°, so 45° is the usual choice where room is short, and every step steeper adds real shrink.

• 10°: 69 1/8" between bends, 1 1/16" of shrink. The gentlest bends, but at this height they span more straight run than most jobs have. It fits every hand-bender shoe from 1/2" to 1-1/4" EMT.
• 22.5°: 31 3/8" between bends, 2 3/8" of shrink. Half of 45°, with less shrink than 30° and an easier pull. It fits every hand-bender shoe from 1/2" to 1-1/4" EMT.
• 30°: 24" between bends, 3 3/16" of shrink. The everyday angle: the spacing is simply twice the height. It fits every hand-bender shoe from 1/2" to 1-1/4" EMT.
• 45°: 17" between bends, 5" of shrink. About 29% less length than 30°, for 1 13/16" more shrink. It fits every hand-bender shoe from 1/2" to 1-1/4" EMT.
• 60°: 13 7/8" between bends, 6 15/16" of shrink. The shortest span and the most shrink, and the hardest on the wire pull. It fits every hand-bender shoe from 1/2" to 1-1/4" EMT.

What the hand-bender table means at 12"

Every bend uses an arc of conduit, and the arc is longer on a bigger shoe. The Greenlee aluminum hand bender's shoes run from a 4 3/16" centerline radius for 1/2" EMT to 9 5/8" for 1-1/4". Two steep bends on a short offset leave little or no straight between the arcs: Too short means they would overlap, and Tight means there is some straight, but less than the shoe needs to grip for the second bend.

A 12" offset is tall enough that every angle leaves straight to spare, even 60° on the 1-1/4" shoe. The only reasons to pick one angle over another are room along the run, shrink and how hard the wire will pull.

Worked example: a 12" offset measured from the end

Say the offset has to be complete 48" from the end of the conduit, where an obstruction or a box begins. The conduit climbs on a slant, so it needs more length than the straight run to get there: the shrink. Add it to the measurement for the second mark, then measure back for the first.

1. Measure the height the conduit has to move, from the surface it sits on now to the surface it has to sit on: 12".
2. Measure from the end of the conduit to the face of the obstruction, 48", and add the 5" of shrink. Mark the second bend at 53".
3. Measure 17" back toward the end and mark the first bend at 36".
4. Bend the first mark to 45°, roll the conduit exactly half a turn, and bend the second mark to 45°. Sight along it to check the two legs are parallel and in one plane.

How a real bender changes the numbers

The tables use the multiplier method, which treats each bend as a sharp corner. A real shoe bends on its centerline radius, so the marks come out a little closer and the offset shrinks a little less. The bigger the radius and the steeper the angle, the bigger the difference. Here is the same 12" offset at 45° on each shoe of the Greenlee aluminum hand bender.

On the 1/2" shoe the marks come out 3/16" closer than the chart and the offset shrinks 3/8" less. On the 1-1/4" shoe the gap grows to 7/16" and 7/8". For a one-off the chart is close enough; where the offset has to land on a mark, use your bender’s own radius.

Mistakes that spoil a 12" offset

• Leaving out the shrink. Marked without it, a 12" offset at 45° finishes 5" closer to the end than you measured, and everything past it comes up 5" short.
• Trusting the rounded shrink. The trade’s 3/8" per inch gives 4 1/2" at 45°, against the exact 5": 1/2" short at this height.
• Measuring to the wrong place. The height is how far the conduit has to move, the same as center to center, not to the far side of the obstruction.
• Rolling more or less than half a turn between the bends, which leaves a dogleg. Draw a line along the top of the conduit before the first bend and keep it on top for the second.
• Mismatched angles. If one bend is 45° and the other a few degrees off, the far leg leaves the original line. Check each bend with a level or the degree scale.