Conduit Bending and Fabrication
Conduit Bending Calculator


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Offsets and Four-Bend Saddles
An offset bend is a double conduit bend with two equal angles bent in opposite directions in the same plane in a conduit run. A four-bend saddle consists of two offsets with a straight section between them. The bending calculator asks for the desired bend angle, the offset rise, and the bend radius. The output screen gives the shrink, the distance between bends, and the adjustment constant for parallel offsets.

Three-Bend Saddles

A three-bend saddle is a saddle consisting of a center bend and two side bends with the center bend having twice the angle of the side bends. It is essentially two offsets that share a common center bend. The bending calculator asks for the desired side bend angle, the offset rise, and the bend radius. The output screen gives the shrink, the distance between bends, and the adjustment constant for parallel offsets.

Gain
Gain is the difference between the sum of the straight distances and the actual length of conduit. In other words, gain is the “shortcut” provided by following the arc of the curve instead of the straight distance. The bending calculator asks for the desired bend angle, the bend radius, and the conduit OD. The output screen gives the gain for that bend.




Bend Angle

One step in bending conduit is choosing the bend angle. A smaller bend angle makes it easier to pull wire through the conduit than a larger bend angle. However, a smaller bend angle takes up more room when rising over an obstacle than a larger bend angle. For offsets and four-bend saddles, typical bend angles are 30° and 45°. For three-bend saddles, typical side bend angles are 22½° and 15°.

Segmented Bend Radius
The bend radius of a segmented bend is the radius of the circular object plus any standoff plus half the conduit OD. For 1 1/2² rigid (OD = 1.900²) bent around a 46² tank with a 1² standoff, the bend radius is 47.95² (46 + 1 + 1.900/2 = 49.95).

Completed Bend Angle

The competed bend angle is the angle that the conduit is bent around the circular object. For example, 1/4 of the way around the object is 90° and 1/2 of the way around the object is 180°.

Number of Shots
The number of shots is the number of small bends used to make the competed segmented bend. A higher number of shots creates a smoother bend.

Offset
Another step in bending an offset is measuring the offset rise needed. The measurements must be taken from the same side of the conduit. This measurement represents the distance from the bottom of the conduit against the wall, ceiling, or other supporting surface to the bottom of the conduit against the obstacle.

Radius
The bend radius is the size of the bend. This may be given on the bender or in the bender manual. Typical values include the following:

Trade size Typical bend radius
1/2"............................4 3/16"
3/4"............................5 1/8"
1"...............................6 1/2"
1 1/4"........................8"
1 1/2"........................8 1/4"
2"...............................9 1/2"
2 1/2"........................12 1/2"
3"...............................15"
3 1/2"........................17 1/2"
4"...............................20"

The calculator defaults to the following:

The values for EMT, up to 1", are for a Greenlee Site-Rite hand bender. The values for EMT, from 1" to 2", and all values of IMC and Rigid up to 2" are for a Greenlee 555 electric bender. The values of EMT, IMC, and Rigid over 2" are for a Greenlee 884/885 hydraulic bender. These values can be overridden by manually entering new values in the Bend Radius box

Conduit OD
The conduit OD is used to calculate the gain.

Trade size EMT Rigid

1/2"...............0.706"............0.840"
3/4"...............0.922"............1.050"
1"..................1.163"............1.315"
1 1/4"............1.510"............1.660"
1 1/2"............1.740"............1.900"
2"...................2.197"............2.375"
2 1/2"............2.875"............2.875"
3"...................3.500"............3.500"
4"...................4.500"............4.500"

Three-Bend Saddles
There are several common methods for calculating the distance between bends when making three-bend saddles. There are different methods because the center bend and the side bends do not use the same benchmarks.

For hand benders, the side bends are made with the arrow benchmark, while the center bend is made with the rim notch or teardrop benchmark. Because of this, the multiplier used to make offset bends must be modified to give acceptable results. For an offset with a 22 1/2° bend, the distance multiplier is 2.61. For a three-bend saddle with a 45° center bend and 22 1/2° side bends, the distance multiplier is changed to 2.5 to account for the difference in benchmarks. For small conduit that can be bent with a hand bender, this method is fairly close and usually gives acceptable results.

For mechanical and electric benders, there are no arrow, rim notch, or teardrop benchmarks. The bends in a three-bend saddle can be made with a benchmark for the center of each bend. There are separate benchmarks for the center of a 22 1/2° bend and a 45° bend. The distance between these benchmarks is approximately the same as the conduit OD. Therefore, the standard offset multiplier of 2.61 can be used, with the addition of the conduit OD.

For mechanical and electric benders, a method sometimes used to compensate for the use of different benchmarks is to use a multiplier of 3.0, instead of the 2.61 used for offsets. However, using this multiplier often results in the distance between bends being too large and the center bend ending up too high above the obstruction. Therefore, this method is not provided with this calculator.

Segmented Bends
A segmented bend consists of a series of small bends made at predetermined locations on a piece of conduit to create one large bend. Each small bend is called a shot.



Shrink
The calculator output is the shrink. Shrink is the amount by which the total run that conduit can cover is reduced because of the extra length required to bend around an obstruction. Shrink is added to the distance to the obstruction. Shrink may be negative for small offsets and large bend radii.

Distance
The calculator output is the distance between the bends. When conduit is bent around an obstruction, it takes two bends to create an offset and three or four bends to create a saddle. For three-bend saddles, the calculator uses a simplified calculation with a multiplier of 2.5 for 22½° side bends.

Parallel OC

The calculator output is the parallel offset constant (Parallel OC). Offset bends can pose a spacing problem when run in a parallel configuration, such as in a conduit rack coming out of a panel or junction box. Conduits that are spaced evenly will crowd one another at the angled sections of the offsets. The layout marks need to be shifted by an amount equal to the product of the conduit center-to-center spacing and the parallel offset constant.

Gain
The calculator output is the gain for the given bend angle and conduit OD. The gain is subtracted from the straight run length when laying out bend marks or when cutting and threading conduit.

Developed Length
The developed length is the amount of conduit used in a bend and can vary from a small section of conduit to an entire 10¢ length or more. The developed is calculated from the bend radius and the completed bend angle.

Bend Angle

The bend angle is the angle of each of the small bends that make up the larger segmented bend. The bend angle is calculated by dividing the completed bend angle by the number of shots. For exposed work, the angle of each small bend should be about 6° or less for best appearance. If the calculated bend angle is more than 6°, the number of shots can be increased at the Input window.

Distance between Bends

The distance between bends is the distance between the centers of each of the small bends that make up the larger segmented bend. The distance between bends is calculated by dividing the developed length by the number of shots. For exposed work, the developed length should be about 4² or less for best appearance. If the calculated distance between bends is more than 4², the number of shots can be increased at the Input window.

  



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