Conduit Bending
 

 

 

 

 


CONDUIT BENDING The NEC® Articles 342 through 362 apply to electrical conduits. It states that the "bends in conduits will be made so that the tubing will not be injured and that the internal diameter of the conduit will not be effectively reduced." In addition, the NEC® has a table that indicates the minimum radius acceptable for various sizes of conduit (T344.24). This radius must be measured from the center line to the center line of the conduit.

It also states that "a run of electrical conduit between outlet and outlet, between fitting and fitting, or between outlet and fitting, will not contain no more than the equivalent of 4 quarter bends (360 degrees total) including those bends located immediately at the outlet or fitting."

When installing conduit, you will need to make bends to go over or around obstacles. Bends of various shapes will be needed, such as right-angle or 90-degree bends, offsets, and saddles. These bends must be made without reducing the inside diameter of the conduit in the bend. You will make most of these bends on the job as part of the installation procedure. They are called field bends. Factory-made bends may be used instead of field bends; however, they will cause you more cutting and threading and they increase the cost of the job. .

Most of the field bends will be done with manual benders or a hot box heater in the case of rigid nonmetallic conduit. Manual benders used to bend rigid conduit and EMT are of two types.

These are the rigid bender, called a hickey (Fig. 6-1), and the one-shot  or star bender (Fig. 6-2). The one-shot bender is normally made for EMT, but some are made to be used for both EMT and rigid. The one-shot bender was given this name because a full 90-degree bend can be made with a single motion. It is also called a star bender because of the star that is found on the head of the bender.  Conduit sizes up to 1-inch rigid or 1 1/ 4- inch EMT can be bent without much trouble with manual benders. Larger sizes are bent with mechanical or hydraulic benders. Hydraulic benders will be discussed in the second year modules. 

Rigid Nonmetallic Conduit Although a complete line of factory elbows (90, 45, or 30 degree) are available, bending PVC conduit (1/ 2 through 2 inch) is accomplished easily with the use of a PVC hot box. A PVC hot box is nothing more than a heater, enclosed by metal having a mirror finish on the inside with openings on each end. To bend PVC conduit, place the conduit inside the hot box, turn the switch on, rotate the conduit until it becomes flexible, remove the conduit and bend it to the desired shape.  In order to help the conduit retain its shape, cap the ends before heating the conduit.

PVC sizes greater than 2” can be bent with the use of a hot blanket.

WARNING The hot box is a heater. If you leave the conduit in long enough, it will BURN. You should use gloves when bending PVC.

 

 

Figure 6-1.- Hickey.

Figure 6-2.- One-shot bender/ Star bender

Electrical Metallic Tubing (EMT) Conduit bending is a precise art form. You will use degrees, angles, measurements and prefigured deductions for radiuses and shrinkage. Combine all these calculations correctly and you will get a finished product that is not only functional but pleasing to the eye, and something to be proud of.

90 DEGREE BENDS - One of the most common bends you will make in the field is the right-angle bend, more commonly called a 90-degree bend, or just a 90. Anyone can make a 90 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 bend the conduit in the right place so that you do not have to cut it. To accomplish this, there are some things you have to know. First, you need to know the distance from the end of the conduit to the back of the 90. This distance is called the stub-up. Second, the radius of the bend takes up a part of the stub-up. This part is called the take-up. The amount of take-up depends on the type and size of conduit you are bending.

AMOUNT OF TAKE-UP FOR 90° BENDS (ONE-shot Benders)

SIZE AND TYPE OF CONDUIT TAKE-UP 

1/ 2" EMT 5"

3/ 4" EMT OR 1/ 2" RIGID* 6 "

1" EMT OR 3/ 4 RIGID* 8 "

1 1/ 4" EMT OR 1" RIGID* 11"

*IMC AND RIGID WILL BE THE SAME

The take up for a bender will normally be marked on the head of the bender.

 

Figure 6-3. Alignment of arrow and take-up mark for bending a 90.

Now, let us see how a 90 is made to fit a specific situation. Suppose you are going to run the conduit from the top of a panel to the ceiling and then horizontally along the ceiling, using 1/ 2-inch EMT and a one-shot bender. The first step will be to measure from the top of the panel to the ceiling. This measurement will give you the stub length. Assume the length is 18 inches. Measure 18 inches from the end of the conduit and make a mark at that point. Next, find the take-up for 1/ 2-inch EMT. The take-up is 5 inches. Now, measure 5 inches back toward the end of the conduit from your first mark and make a second mark. This measurement gives you the take-up. Place the conduit on the floor with the stub in front of you. Align the bender arrow with the take-up mark, as shown in Figure 6-3. Put one foot on the footrest and hold the handle with both hands. Apply pressure on the footrest as you pull the handle until the handle is at about a 30- degree angle with the floor, as shown in Figure 6-4. You should now have a 90-degree bend with an 18-inch stub. Remember: Heavy foot pressure is critical to keep the EMT in the bender groove and prevent kinked conduit. To check that the bend will fit the situation we started with, you can place it next to anything that you know is a right angle and measure from the floor to the end of the stub. If the bend is not a full 90, place the bender back on the conduit, and pull more bend. If it is more than a 90, place the handle of the bender over the end of the stub, place one foot on the conduit on the floor, and spring the stub back.

BACK-TO-BACK BENDS.- The back-to-back bend is actually two adjacent 90s made in the same piece of conduit. You make the first 90 with the amount

Figure 6-4.- Right-angle bend, 90.

of stub you need, as described previously. To determine where to place the next stub, you first need an outside-to- outside measurement. This measurement is the distance from the back of the first bend to the point where you want the back of the second bend.

Two methods are used for making the second bend. The first is to subtract the take-up, use the arrow on the bender, and pull the bend in the same direction as you did the first bend. The second method, and probably the easiest, is to turn the bender around, line up the star on the bender with your outside-to-outside measurement, and pull the bend in the opposite direction.

Table 6-5.- Offset Bending Formula

 

OFFSET BENDS - 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. The angle of the bend in an offset depends on several things: how much offset is needed, how much room there is where the offset is going to be placed, and the type of obstacle you are avoiding. There is no way to mark the conduit for a box offset. The amount of bend and the distance between bends are estimated. The key to making good box offsets is practice.

Figure 6-6.- Bending an offset.

Figure 6-7.- Bender degree markings.

To make accurate offsets of 2 inches or more in depth, you can mark a predetermined distance on the conduit. The distance between the bends depends on the depth of the offset and the amount of bend that you are going to use. Table 5-3 shows the formula to use to find the distance to be marked on the conduit. It also shows the constant multiplier that must be used in the formula for the angle of bends you intend to use and the shrinkage per inch.

Let us use an example to see how the formula works. Suppose you need to avoid a part of a obstruction that requires an 8-inch offset, you are going to use 30-degree bends, and you are 40 inches from the obstruction. Table 5-3 shows that the constant multiplier for 30-degree bends is 2 and the shrinkage of one-fourth inch equals 2 inches for a total of 42 inches. Using the formula, multiply the depth of the offset (8 inches) times the constant multiplier (2), and the result is the distance needed between the bends (16 inches).

You place the first mark at 42 inches, the second 16 inches apart, and using the arrow of the bender, make a 30-degree bend on the same side of each mark, as shown in Figure 5-46. In this example, a 30-degree bend gives us the offset we 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, in this case 30-degree at each mark, is obtained by using the degree markings on the bender, as shown in Figure 6-7.

Notice that the side of the conduit closest to the bender is in line with the 30-degree marking on the bender. If you have a bender without markings, a protractor (works especially well on larger conduit) can be used or you can lay a 30-degree angle out on a large piece of paper or on the floor with chalk. Then check the bend against the 30-degree angle you have laid out.

Normally, offsets are made by making the first bend on the floor and the second bend in the air, as shown in Figure 6-8.

Figure 6-8.- Bending on the floor and in the air.

Figure 6-9.- Bending a conduit saddle bend.

SADDLE BENDS.- Saddles may be necessary when obstructions (Fig. 6-9) are encountered. The most common method of straddling an obstacle is the three-bend saddle, using a 45-degree center bend and two opposing 22 1/ 2-degree bends. All measurements begin with locating the center of the obstruction on the conduit and marking it as Point A. Table 5-4 shows shrinkage factors and distances for marks "B" and "C." The formula is from mark "A," add 3/ 16 of an inch times saddle depth and distance from mark "A" to marks "B" and "C" = 2.5 inches times saddle depth.

Figure 6-9 is an example of placing a 4-inch saddle around a conduit that is 15 inches from a junction box. Following the bending sequence shown, pay close attention to the orientation of the bender head. Remember to use the star arrow on the bender to align Point A for the 45-degree center bend and the front arrow to align the bender with marks "B" and "C" for the 22 1/ 2-degree bends. Be sure to line up all bends in the same plane. This procedure is true of all bends, not just a saddle.

Table 6-10.- Bending Conduit Saddle Table, Shrinkage Factors, and Distances

 

Rigid Metal Conduit The procedures for making the different types of bends discussed thus far have all been with a one-shot bender. The same bends can be made with rigid conduit. A hickey bender can be used on rigid metal conduit also although the procedures are slightly different. For instance, to make a 90-degree bend in 1/ 2-inch rigid metal conduit, you should take the steps shown in Figure 6-11. Let us say you need a 20-inch stub-up at the end of the 1/ 2-inch stick of rigid conduit. The steps for bending with a hickey are as follows:

Mark off 20 inches from the end of the conduit. Determine the take-up for 1/ 2-inch rigid conduit.

Make a second mark 6 inches back toward the end of the conduit. Place the hickey at the second mark and pull about 30 degrees of bend. Move the bender toward the 20-inch mark about 2 inches. Pull another 30 degrees of bend. Move the bender to where the heel of the bender is on the 20-inch mark and complete the 90- degree bend.

Figure 6-11.- Bending a 90 with a hickey.

Figure 6-12.- Bending with a hickey using small bites.

Since the hickey bender does not usually have degree markings on it, you have to estimate the amount of bend you are making with each bite. Small bites, as shown in Figure 6-12, reduce the possibility of crimping or kinking the conduit.

Mechanical Benders Mechanical benders are designed to bend conduits using a built-in ratchet for fast, no kink, bends. Depending on the make and model, they are portable and easy to use. Equipped with different shoe sizes, they will bend EMT conduit from 3/4 inch through 2 inch, rigid and aluminum conduit 1/2 through 1 1/2 and IMC 1/ 2 through 1 1/4. Minimum stub lengths and take-up deductible inches vary from the hand benders just discussed. While the bending principles are the same, you will need to check with the manufacturers directions and bending charts.

I also recommend that you ask your foreman if you can take a piece of ˝” conduit and a bender home occasionally so you can practice making bends. Electricians consider conduit bending an art form. The more you practice the better you will become.

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Edited, Compiled and Published by Ted “Smitty” Smith Sr.

 

 

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