Offset bends are used to move a run of conduit from one plane to another. An offset is normally used to bend the conduit around an obstruction, or to relocate the conduit close to a structural member to make it easier to fasten the conduit. Figure 2 shows an example of an offset bend.
There are several factors that an electrician must determine prior to fabricating an offset. First, he/she must determine the center to center distance of the offset. This dimension is 10″ in Figure 2. Next, he/she must determine the angle of bend to use for the offset. The angle used in Figure 2 is 30º, which is the most popular angle used for bending offsets. After determining these two dimensions, the electrician can then determine the distance between bends needed to make the bends. A trigonometric function, the Cosecant, is used to determine the distance between the centers of the two bends used to make the offset. The Cosecant of an angle is defined as the length of the hypotenuse of a 90º triangle divided by the length of the opposite side of the triangle. Refer to Figure 1.
Figure 1 shows an example of an offset bend. The center to center dimension of the offset is 10″. The angle used to make the bends for the offset is 30º. The Cosecant of 30º is 2.0. The formula used to determine the center to center distance between bends is:
The center to center dimensions of the bends is equal to the desired size of the offset times the cosecant of the angle used to make the bends.
C = 10 x 2, or C = 20″.
30º bends are popular for making offsets, because the cosecant of 30º is 2. Also, most small EMT hand benders are designed so that the bender handle is straight up when a 30º bend has been made with the conduit on the floor. It is also easier to pull wire through a conduit with 30º bends than it is for a conduit with 45º or 60º bends. 45º or 60º bends are sometimes used if the electrician has to bend a large offset in a short distance.
30º bends are too great with most hand benders for offsets less than 4″ center to center. A popular bend for small offsets is 22 1/2º. The table below list several popular bending angles, and the cosecant of the angles.
Offset Calculator Instructions:
Using this form will enable you to calculate the distance between bends for an offset. You must:
You will be given the Cosecant of the the angle selected, and the distance between bends to mark the conduit. Remember, the offset is calculated ‘center to center’.