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3-2 Types of Bends
Conduit installations are normally referred to as runs of conduit. A run of conduit is the conduit, fittings, straps, conductors, and bends needed from one opening to the next (for example, from the panel board to the first outlet box or from the first outlet box to the second outlet box). In a run of conduit, there cannot be more than the equivalent of four 90° bends, for a total of 360°. The purpose of allowing only so many bends in a run of conduit is to help in pulling conductors into the conduit. Experience has taught that if more than 360° of bends are used, it is very difficult to pull conductors through the bends (Figure 3-2).
Conduit bodies are available in the following configurations: elbow back (LB), elbow right (LR), elbow left (LL) and a T. The configuration of each is determined based on the location of the removable cover (Figure 3-3).
By using a conduit body in a run, you provide an opening for pulling the conductors without having to mount a box. At the same time, you can make a turnaround or go over an obstacle and maintain a neat conduit installation. The turn or 90° turn made by the conduit body does not count as one of the four allowable bends in a run. As a matter of fact the conduit body is identified as an outlet box.
One of the most common bends you will make in the field is the right-angle bend, more commonly called a 90° bend or just a 90. It can be used for going around an inside corner, into the top or bottom of a box from a horizontal run, or over an object.
Anyone can make a 90° bend in a stick of conduit and then cut it off to make it fit the situation, but this practice wastes time and material. The secret is to find out where the bend is needed, mark the conduit accordingly, and make the bend in the right place. This practice saves time and material. Before you can determine where to place your bender on the conduit, there are some things you must know. First, there are two lengths on the conduit that must be considered, from one end of the conduit to the 90° bend and then from the 90° bend to the other end of the conduit. The shorter of these two lengths is called the stub end, or simply the stub (Figure 3-4A), and the longer is the running end. Second, the radius of the bend takes up a part of the stub. This part of the stub is called take-up and is shown in Figure 3-4B. The amount of take-up depends on the type and size of the conduit you are bending (Table 3-1).
In the following example, you are going to make a 90° bend using 1/2-inch EMT conduit and the EMT bender. You are going to run the conduit from the top of a panel to the ceiling and then horizontally along the ceiling. Measure from the top of the panel to the ceiling. This will give you the stub length of 18 inches. Measure 18 inches from the end of the conduit and make a mark (Figure 3-4).
Look at Table 3-1 to find out what the take-up is for 1/2-inch EMT conduit. The take-up is 5 inches. Measure back 5inches from the first mark toward the end of the conduit and make a second mark as shown in Figure 3-5.
Hold the bender in one hand with the lip on the floor pointed toward the stub end. Use the other hand to place the conduit in the bender. Align the bender arrow with the take-up mark. Put one foot on the footrest and hold the handle with both hands. To make the bend, apply pressure on the footrest as you pull on the handle until the handle is parallel with the floor. It is OK to go slightly beyond 90° with the bend, in fact it is preferred, because it is easy to bring it back to 90°.
You should now have a 90° bend with an 18-inch stub (Figure 3-6). To see whether the bend will fit properly, place it next to something that has a right angle (for example, in the corner where the floor and wall meet).
If the bend is more than 90°, you can stand on the running end and push out on the stub end, a little at a time, until it is 90°. If the stub is too short or if the conduit is too long to push back, place the handle of the bender over the end of the stub and, with one foot on the conduit on the floor, spring the stub back (right-angle bends should always be made with the conduit and the bender on the floor).
In this example, you are going to make a 90° bend in the conduit and run it along the wall. The first thing you must do is establish a reference point using the following steps:
Step 5. Measure from box A to the reference point and add this measurement to the measurement between box B and the reference point. Deduct the gain (Table 3-2). This will give you the length for the piece of conduit you need to run between boxes A and B (Figure 3-7).
In the following example, you are going to run 1/2-inch EMT from box "A" to box "B." The measurement from box "A" to the reference point is 15 inches and from box "B" to the reference point is 30 inches. Add the two measurements together to get the total length of 45 inches. Deduct the "bender gain," which is 2 5/8 inches.
With this information, you know that you must subtract the "gain" so that the conduit will not be too long (45 inches 2 5/8 inches = 42 3/8 inches). Cut a piece of conduit 42 3/8 inches long to go from box "A" to box "B." After the EMT is cut and reamed, the next thing to do is bend offsets and then a 90 in the conduit.
An offset bend is two equal bends in opposite directions. It is used to avoid contacting a part of the structure or to bring the conduit out from the structure to match a knockout in a box or panel.
Figure 3-8 shows an offset into a utility box. The angle of the bends in an offset depends on several things: the amount of offset that is needed, the amount of room there is where the offset is going to be placed, and the type of obstacle you are avoiding. The offset shown is usually about 1/2 inch deep, and the bends are about 8º angles. Often, these bends will need to be made on both ends of the conduit to enter two boxes. To make this type of offset, make a mark on each end of the conduit 1 1/2 inches from the ends. Make another mark at each end 4 1/2 inches from the end. Place the conduit in the bender on the 1 1/2-inch mark and make an 8º angle bend on both ends. Turn the bender over and make bends on the 4 1/2-inch marks with the bender head in the air. Once the bends are made, check them by placing the conduit on a flat surface and putting a tape measure behind the conduit and measuring the distance from the bottom of the conduit to the flat surface. If you do not have a 1/2-inch offset, place the conduit back in the bender with the bender head in the air and make adjustments until you have a 1/2-inch offset. The key to making a good box offset is practice. Notice that after the bends are made, the conduit sections on each end of the offset are parallel to each other.
Table 3-3 is a guide for offsets. The following example shows how to figure offsets. For example, if a 3-inch offset is needed, the distance between the bends would be 6 inches¾if the first mark was 2 inches from the end of the conduit, the second mark would be at 8 inches from the end of the conduit. The angle of bend would be 30º and the conduit length loss would be 3/4 inch; therefore, the conduit should be 3/4 inch longer to make up for the loss (Figure 3-9).
Table 3-4 shows an offset formula to use. The following paragraphs explain how to use this table. Multiply the offset angle and the multiplier to find the distance between the offsets. The angle that you use depends on how much room there is on your site to run the conduit. For example, if you need a 5-inch offset and use a 30º angle; the constant multiplier would be 2 (5 X 2 = 10). The distance between the bends would be 10 inches. The conduit length loss will be 1/4 inch of conduit for every inch of offset; therefore, add 1 1/4 inch of conduit to the length.
Place the marks for the bends 10 inches apart. Using the arrow of the bender, make a 30º bend on the same side of each mark (Figure 3-9). A 30º bend will give you the offset you need. If you make both bends inside the marks, you will end up with much less than the desired offset. If you make both bends outside the marks, you will have too much offset. The amount of bend is obtained by using the degree markings on the bender.
Once the bends have been made, verify the offset depth by placing it on a flat surface and measuring the distance from the bottom of the conduit to the flat surface.
The back-to-back bend is actually two adjacent 90° bends made in the same piece of conduit. Make the first 90° bend with a certain amount of stub as described previously. To determine where to place the bender for the second bend, you must first have an outside-to-outside measurement. This measurement is the distance from the back of the first bend to where you want the back of the second bend. You must then transfer this measurement to the conduit and make a mark. The easiest way to make a back-to-back bend is to turn the bender around, line up the star of the bender with your outside-to-outside measurement, and pull the bend in the opposite direction (Figure 3-10).
|David L. Heiserman, Editor||
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Revised: June 06, 2015