NCCER Electrical L2/M4

Embed

Social
Select the file type you wish to download
Slide Content

Slide 2  Objectives
 When trainees have completed this lesson, they should be able to do the following:
 1. Describe the process of conduit bending using power tools.
 2. Identify all parts of electric and hydraulic benders.
 3. Bend offsets, kicks, saddles, segmented, and parallel bends.
 4. Explain the requirements of the National Electrical Code® (NEC®) for bending conduit.
 5. Compute the radius, degrees in bend, developed length, and gain for conduit up to six inches.
 Conduit Bending 2620414

Slide 3  Performance Tasks
 1. Use an electric or hydraulic bender to bend a 1" conduit stubup to an exact distance of 151⁄4" above the deck.
 2. Make an offset in a length of conduit to miss a 10" high obstruction with a clearance between the obstruction and the conduit of not less than 1" nor more than 11⁄2".
 3. Make a saddle in a length of conduit to cross an 8" pipe with 1" clearance between the pipe and the conduit.
 Conduit Bending 2620414

Slide 4  1.0.0 – 2.1.0
 Conduit Bending 2620414
 Introduction; NEC® Requirements
 • The NEC® specifies a minimum radius for conduit bends in order to avoid damage to both the conduit and conductors.
 • In addition, the total of all bends in a conduit run must not exceed 360 degrees.

Slide 5  1.0.0 – 2.1.0
 Conduit Bending 2620414
 NEC® Minimum Requirements for Radius of Conduit Bends – OneShot and FullShoe Benders
 Per NEC Chapter 9, Table 2, the minimum radius to the centerline of the conduit for oneshot and fullshoe benders must be no less than that listed here.

Slide 6  1.0.0 – 2.1.0
 Conduit Bending 2620414
 NEC® Minimum Requirements for Radius of Other Conduit Bends
 Per NEC Chapter 9, Table 2, the minimum radius to the centerline of the conduit of other bends must be no less than that listed here.

Slide 7  3.0.0
 Conduit Bending 2620414
 Types of Bends
 • Basic bends include elbows, offsets, saddles, and kicks.
 • An elbow provides a 90degree change in direction. Factory elbows are used to save time when installing runs of large conduit.
 • Segmented bends can be used to provide concentric bends with multiple conduit runs.

Slide 8  3.0.0
 Conduit Bending 2620414
 Applications of Conduit Offsets
 • Offsets consist of two equal bends and are used to route conduit around obstructions.
 • Offsets are also used to route conduit to outlet boxes, cabinets, panelboards, and pull boxes.

Slide 9  3.0.0
 Conduit Bending 2620414
 Practical Application of a Saddle Bend
 • Saddle bends can be used to route conduit around obstructions such as ductwork or piping.
 • Both three bend and fourbend saddles can be used.

Slide 10  3.0.0
 Conduit Bending 2620414
 Kick
 • A kick is a single change in direction.
 • Kicks are often used to route conduit up through deck work.

Slide 11  4.0.0 – 4.1.1
 Conduit Bending 2620414
 The Geometry of Bending Conduit
 • The offset of a conduit bend forms the hypotenuse of a right triangle.
 • The mathematics of right triangles can be used to find unknown measurements.

Slide 12  4.0.0 – 4.1.1
 Conduit Bending 2620414
 Trigonometry Fundamentals of a Right Triangle
 • Trigonometric equations can be used to find an unknown side or angle.
 • These equations can also be applied to determine conduit measurements, such as the rise or stubup and the distance between bends.

Slide 13  4.0.0 – 4.1.1
 Conduit Bending 2620414
 Kick Example
 • The length of the side opposite (O) can be found by rearranging the cosecant equation to solve for O (opposite = hypotenuse/cosecant).
 • To determine the height of this kick, the length of the hypotenuse (20") is divided by the cosecant of the angle of 30 degrees (2) to arrive at a height of 10".

Slide 14  4.2.0 – 4.2.1
 Conduit Bending 2620414
 Circle
 • A circle is a closed, curved line with all points equidistant from the center.
 • The distance from the center point to the edge is the radius and the distance through the center to the other side is the diameter.
 • Concentric circles have a common center but different radii.

Slide 15  4.2.0 – 4.2.1
 Conduit Bending 2620414
 Parts of a Circle Related to Conduit Bending
 A 90degree bend in conduit represents a quarter of a circle.

Slide 16  4.2.0 – 4.2.1
 Conduit Bending 2620414
 Unit Circle
 • A unit circle has a given radius of one.
 • To find the circumference of a circle, multiple 2 times the value of pi (3.14) times the radius (C = 2πR).

Slide 17  4.2.0 – 4.2.1
 Conduit Bending 2620414
 π and 2π
 • Using a unit circle with a radius of one, the circumference is equal to 2π.
 • Half of the circle equals 2π/2 or simply π, and a 90° bend equals π/2 or 1.57.
 • Multiplying 1.57 times the radius provides the distance from 0° to 90°. This is known as the developed length.

Slide 18  4.3.0 – 4.3.1
 Conduit Bending 2620414
 Equations
 • Circumference = π x diameter
 • Length of arc = 1.57R
 • Gain = R x gain factor

Slide 19  4.3.0 – 4.3.1
 Conduit Bending 2620414
 Gain Factors
 • Find the gain factor for a given conduit size and degree of bend.
 • Multiply the gain factor by the centerline radius of the bend and subtract it from the conduit length to find the gain.

Slide 20  4.3.0 – 4.3.1
 Conduit Bending 2620414
 Decimal Equivalents of Some Common Fractions

Slide 21  4.3.0 – 4.3.1
 Conduit Bending 2620414
 BacktoBack 90° Bends
 • When making backtoback bends, calculate the gain by multiplying the gain factor by the centerline radius of the bend.
 • Multiply the gain by two and subtract from the overall length.
 Next Session…
 Mechanical Benders

Slide 22  5.0.0
 Conduit Bending 2620414
 Mechanical Benders
 • Hickeys and EMT bending tools are used on smaller conduit and runs with few bends.
 • Mechanical benders can be used to duplicate multiple bends with minimal effort. Select the correct bender shoe for the type and size of conduit in use.

Slide 23  5.0.0
 Conduit Bending 2620414
 Bending Protractor
 • Before making a bend, the desired angle is set using an adjustable pointer on the bender.
 • Use a bending protractor to check the angle before making multiple bends.

Slide 24  5.0.0
 Conduit Bending 2620414
 Conduit
 • Benders can be charted using a scrap piece of conduit.
 • This process can be used to find the minimum rise, gain, and centerline distances for various bends.

Slide 25  5.0.0
 Conduit Bending 2620414
 Conduit with 10" Mark
 To begin charting a bender, place a mark at a given distance from the end of the conduit (in this case, 10").

Slide 26  5.0.0
 Conduit Bending 2620414
 Kick of 15°
 • Place the bender arrow on the 10" mark and a bending protractor on the conduit in front of the bend.
 • Bend the conduit until the protractor reads 15°.

Slide 27  5.0.0
 Conduit Bending 2620414
 Conduit and Straightedge
 Align a straightedge with the inside of the bend and scribe a line across the bend.

Slide 28  5.0.0
 Conduit Bending 2620414
 Conduit and Horizontal Straightedge
 Next, align a straightedge with the horizontal conduit and scribe another line across the bend.

Slide 29  5.0.0
 Conduit Bending 2620414
 Center of Bend
 • The point at which the two lines cross represents the center of the bend.
 • Measure from the 10" mark to the centerline of the bend and chart this measurement for 15°.
 • Repeat this process for other bends.

Slide 30  5.0.0
 Conduit Bending 2620414
 90° StubUp
 • To find the minimum rise, place the protractor on the bender and bend the conduit until it reads 90°.
 • Measure from the back of the conduit to the 10" mark. This is the minimum stubup length.

Slide 31  5.0.0
 Conduit Bending 2620414
 90° Elbow
 • To determine the gain of a bender for a 90° bend, measure the length of both sides of the scrap piece of conduit.
 • Add the two measured lengths and subtract the original length of the conduit. Chart this as the gain of the bender.

Slide 32  6.0.0 – 7.1.0
 Conduit Bending 2620414
 Mechanical StubUps; Mechanical Offsets
 • The deduct chart on the bender lists information for various stubups and offsets.
 • To bend a mechanical stubup, subtract the chart value for the given rise from the total rise. Place the bender on this measurement and bend the conduit.
 • To bend an offset, mark the distance to the first bend, then find the distance between bends on the chart for the given angle. Bend the conduit.
 Next Session…
 Electric and Hydraulic Conduit Benders

Slide 33  8.0.0 – 8.1.1
 Conduit Bending 2620414
 • Larger conduit is bent using electrical or hydraulic benders.
 • Electric benders can be used to make oneshot bends in ½" through 2" EMT, IMC, or RMC.
 • Bender charts include deduct and springback figures, along with offset information. Springback occurs when conduit relaxes slightly after bending.
 Electric and Hydraulic Conduit Benders

Slide 34  8.2.0 – 8.2.3
 Conduit Bending 2620414
 • Hydraulic benders can be used to bend conduit up to 6" trade size.
 • Hydraulic benders are available with both oneshot and segmented bending shoes.
 • Aluminum conduit is prone to wrinkling and scoring and tends to produce inconsistent bends.
 Hydraulic Conduit Benders

Slide 35  8.2.0 – 8.2.3
 Conduit Bending 2620414
 • To lay out a oneshot stubup, add the rise and leg length, then subtract the gain.
 • Subtract half of the gain from either leg length to find the center of the bend.
 • Calculate the developed length and the length of conduit required.
 Laying Out StubUps

Slide 36  8.2.0 – 8.2.3
 Conduit Bending 2620414
 Dimensions of StubUps for Various Sizes of Conduit

Slide 37  8.2.0 – 8.2.3
 Conduit Bending 2620414
 Laying Out Segment Bends
 • To lay out a segment bend, multiply the radius by 1.57 to determine the developed length.
 • Locate the center of the required bend. Once the center is found, it is easy to locate the other bend marks.
 • Use an odd number of shots so there are an equal number of bends on either side of the center mark.

Slide 38  8.2.0 – 8.2.3
 Conduit Bending 2620414
 Specifications for Sample Bend

Slide 39  8.2.0 – 8.2.3
 Conduit Bending 2620414
 Conduit Placed in Hydraulic Bender for Segment Bends
 • Check the distance between the first and last bend marks before starting the first bend.
 • After positioning the conduit in the bender, attach the pipe bending degree indicator in a convenient location.

Slide 40  8.2.0 – 8.2.3
 Conduit Bending 2620414
 Conduit Center
 • To find the developed length, multiply the radius by 1.57 to find the developed length of the bend.
 • The segments are laid out on either side of the centerline.

Slide 41  8.2.0 – 8.2.3
 Conduit Bending 2620414
 Conduit Segments
 • Divide the developed length by the number of shots to determine the distance between segments.
 • Divide 90 degrees by the number of shots to determine the degrees per shot.
 Performance Task
 This session will conclude with trainees using an electric or hydraulic bender to bend a 1" conduit stubup to an exact distance of 151⁄4" above the deck.
 Next Session…
 Segment Bending Techniques

Slide 42  9.0.0
 Conduit Bending 2620414
 Segment Bending Techniques
 • The four methods of measuring segment bends include using a bend degree protractor, a magnetic angle finder, the amount of travel method, and the number of pumps method.
 • Precise measurements are necessary—even a small segment bending error will be compounded as the bend is completed.

Slide 43  9.0.0
 Conduit Bending 2620414
 Radians and Degrees
 • All angles in a unit circle can be calculated in relation to pi using the circumference formula.
 • To find the developed length of the conduit at 30 degrees, divide the value of pi by six and multiply it by the radius of the bend.

Slide 44  9.0.0
 Conduit Bending 2620414
 Bend Centerline Distance
 The distance between the centerlines of each bend is found by rearranging the cosecant formula to solve for the hypotenuse:
 Hypotenuse = opposite x cosecant
 Hypotenuse = 30" x 2 = 60"

Slide 45  9.0.0
 Conduit Bending 2620414
 Bend Centerline
 The next step is to find the centerline of each bend by dividing the developed length by two.

Slide 46  9.0.0
 Conduit Bending 2620414
 Bend Segments
 • When building a 90degree sweep, the rule of thumb is 21 shots or 20 segments.
 • A 30degree sweep would use seven shots or six segments.

Slide 47  9.1.0
 Conduit Bending 2620414
 Concentric Bending
 • When routing two or more parallel runs of conduit in the same direction, the best results are obtained using concentric bends.
 • The bend for the innermost conduit is calculated first, then the second radius is formed by adding the outside diameter of the first conduit to the first radius and the desired spacing.

Slide 48  9.2.0 – 9.3.0
 Conduit Bending 2620414
 Offset Bends

Slide 49  9.2.0 – 9.3.0
 Conduit Bending 2620414
 Think About It: Concentric Bends
 What does concentric mean? Why can’t you just bend all your conduit sections to the same radius and lay them side by side?

Slide 50  9.2.0 – 9.3.0
 Conduit Bending 2620414
 Position of Conduit in Bender for Making Offsets
 • To make an offset, the conduit is positioned in the bender and the shoe is used to make the first 45degree bend.
 • The conduit is reversed in the bender and the next 45degree bend is made at the second mark.

Slide 51  9.2.0 – 9.3.0
 Conduit Bending 2620414
 24" Offset
 • To find the distance between bend points, multiply the offset required by the cosecant of the bending angle.
 • The amount of conduit to be added to the straight distance entering the junction box is found using the cosine formula (adjacent = cosine x hypotenuse).

Slide 52  9.2.0 – 9.3.0
 Conduit Bending 2620414
 20" Offset
 • It is better to use multiple shots when making offsets to provide a smoother bend and easier conductor installation.
 • Concentric offsets are made by adding the radius of the first pipe to the outside diameter of the first pipe and the desired spacing between the runs.

Slide 53  9.3.1
 Conduit Bending 2620414
 Saddle Bends
 • To make a saddle bend, the bend is calculated using bending charts.
 • Make the two smaller bends first, then make the third larger bend.

Slide 54  9.3.1
 Conduit Bending 2620414
 Saddle Table
 • Hydraulic benders can be used to make saddle bends in conduit up to four inches inside diameter (ID).
 • Bending charts are used to find the spacing between bends for various angles and sizes of conduit.

Slide 55  9.3.1
 Conduit Bending 2620414
 36" Saddle

Slide 56  9.3.1
 Conduit Bending 2620414
 Saddle

Slide 57  9.3.1
 Conduit Bending 2620414
 Cosine Function
 • Subtract the length of the adjacent side from the hypotenuse measurement to find the amount of additional conduit required to make the bend.
 • To calculate the length of the adjacent side, use the cosine formula (adjacent = cosine x hypotenuse).

Slide 58  9.3.1
 Conduit Bending 2620414
 Conduit Layout
 To find the total amount of conduit required from the end of the existing conduit to the junction box, add the straight line distance of 15' to the difference between the hypotenuse and side adjacent two times:
 15' + 15.29" + 15.29" = 17'6.58"
 Performance Tasks
 This session will conclude with trainees making offsets and saddle bends using a hydraulic bender.

Slide 59  10.0.0 – 10.2.0
 Conduit Bending 2620414
 Tricks of the Trade
 • A dog leg occurs when the conduit centerline is not maintained for both bends of an offset or for the four bends of a saddle.
 • Doglegs can be avoided using an antidog device, which is a small setscrew clamp with a builtin level. A piece of Unistrut® can also be used to keep the conduit aligned properly during bending.

Slide 60  10.0.0 – 10.2.0
 Conduit Bending 2620414
 25" Offset
 • A table corner or the corner of a sheet of plywood can be used to determine the amount of additional conduit needed to travel from one point to another after a bend has been made.
 • Use the corner of the table/plywood to establish a right triangle, then use the cosecant formula to find the hypotenuse.

Slide 61  10.0.0 – 10.2.0
 Conduit Bending 2620414
 Extra Conduit

Slide 62  11.0.0 – 12.0.0
 Conduit Bending 2620414
 PVC Conduit Installations; Bending PVC Conduit
 • PVC conduit is easily cut and joined in the field using a hacksaw or PVC cutters and solventcement.
 • PVC heating units are used to make various bends in PVC conduit.

Slide 63  11.0.0 – 12.0.0
 Conduit Bending 2620414
 Plywood Template
 • If several identical bends are required, a plywood template can be fabricated.
 • The heated conduit section is placed in the template and bent to the desired angle.

Slide 64  11.0.0 – 12.0.0
 Conduit Bending 2620414
 Some PVC Bends May be Formed by Hand
 • Smaller PVC conduit can be heated and bent by hand to fit the installation.
 • This method is useful for making blind bends or compound bends using smaller sizes of PVC.

Slide 65  11.0.0 – 12.0.0
 Conduit Bending 2620414
 After the Bend is Formed, Wipe a Wet Rag Over the Bend to Cool It

Slide 66  11.0.0 – 12.0.0
 Conduit Bending 2620414
 Typical Plug Set
 • Place airtight plugs in each end of the conduit section before heating.
 • Plugs prevent the conduit from flattening when making the bend.

Slide 67  11.0.0 – 12.0.0
 Conduit Bending 2620414
 PVC Expansion Rates
 Next Session…
 Wrap Up

Slide 68  Wrap Up
 321
 3 – Write 3 important things learned during class
 2 – Write 2 questions you have about the material
 1 – Write 1 thought you had about the material
 Conduit Bending 2620414

Slide 69  Next Session…
 MODULE EXAM
 Review the complete module to prepare for the module exam. Complete the Module Review as a study aid.
 Conduit Bending 2620414