1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA PRP 3-2009 (R2016)Expansion Epoxy Based Fittings for RTRC Rigid Nonmetallic ConduitNEMA PRP 3-2009 (R2016) Page 1 2016 National Electrical Manufacturers Association A NEMA Polymer Raceway Products Document PRP 3-2009 (R2016)
2、 Expansion Epoxy Based Fittings for RTRC Rigid Nonmetallic Conduit Published by National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2016 National Electrical Manufacturers Association. All rights, including translation into other languag
3、es, reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American copyright conventions. NEMA PRP 3-2009 (R2016) Page 2 2016 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The inf
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13、olely the responsibility of the certifier or maker of the statement.NEMA PRP 3-2009 (R2016) Page 1 2016 National Electrical Manufacturers Association Thermal expansion and contraction have a significant effect on long straight runs of conduit. For this application, O-ring expansion fittings are used
14、 to accommodate changes in length. This prevents potentially harmful thermal stresses in the conduit itself or in any supporting structures. Expansion Fittings Required Section 355.44 of the National Electrical Code (NEC) requires that expansion fittings be installed for RTRC to compensate for therm
15、al expansion and contraction where the length change is anticipated to be inch or 6 mm or greater in a straight run between securely mounted items. Securely mounted items include boxes, cabinets, elbows, and other conduit terminations. Table 355.44 of the NEC shows the expansion characteristics of R
16、TRC Rigid Nonmetallic Conduit for different temperatures. When are expansion fittings used? Knowing when to use an O-ring expansion fitting is as important as knowing how to use it. Expansion fittings are predominantly used in aboveground installations where the length change is anticipated to be in
17、ch or 6 mm or greater. When are expansion fittings used? (continued) Expansion Epoxy Based Fittings for RTRC Rigid Nonmetallic Conduit All construction materials expand and contract with fluctuations in temperature. These temperature changes affect Reinforced Thermosetting Resin Conduit (RTRC) diffe
18、rently than other common materials such as steel or PVC. For example, the coefficient of thermal expansion for RTRC (1.5 10-5in./in./F or 2.710-5cm/cm /C) is slightly more than twice that of steel and is 50% that of PVC. RTRC has a coefficient of expansion of 1.5105in./in./F or 2.710-5cm /cm / C. A
19、19.68 foot or 6 meter section will change in length about 3/16” or 4.8 mm with a change in temperature of 120F or 66.7C. This equates to slightly more than 1” or 44 mm over a 100 foot or 30.5 m run. NEMA PRP 3-2009 (R2016) Page 2 2016 National Electrical Manufacturers Association Changes in conduit
20、temperature outdoors can exceed 140F or 77.8C considering the heat of summer and cold of winter. This means a 100-foot or 30.5-meter run of fiberglass conduit could change approximately 2 inches or 64 mm in length between summer and winter. If not compensated for with expansion fittings, this change
21、 in length can cause unsightly conduit bowing, distorted boxes, or broken couplings or fittings. The anticipated expansion and contraction per 100 feet or per meter for various lengths of runs and temperature changes is given in Table 355.44 of the NEC The table below expresses this expansion and co
22、ntraction per 100 feet or 30.5 meters of conduit for various temperature changes. Since the C changes in the table below are conversions of the F changes, the expansion values provided are for different C changes than Table 355.44. Expansion Characteristics of RTRC Coefficient of Thermal Expansion =
23、 1.5 10-5in./in./F or 2.7 10-5cm/cm/C Temperature Change Degrees F C Length Change per 100 ft/30.5 m in mm Temperature Change Degrees F C Length Change per 100 ft/30.5 m in mm Temperature Change Degrees F C Length Change per 100 ft/30.5 m in mm Temperature Change Degrees F C Length Change per 100 ft
24、/30.5 m in mm 5 2.8 0.09 2.3 55 30.6 0.99 25.1 105 58.3 1.89 48.0 155 86.1 2.79 70.9 10 5.6 0.18 4.6 60 33.3 1.08 27.4 110 61.1 1.98 50.3 160 88.9 2.88 73.2 15 8.3 0.27 6.9 65 36.1 1.17 29.7 115 63.9 2.07 52.6 165 91.7 2.97 75.4 20 11.1 0.36 9.1 70 38.9 1.26 32.0 120 66.7 2.16 54.9 170 94.4 3.06 77.
25、7 25 13.9 0.45 11.4 75 41.7 1.35 34.3 125 69.4 2.25 57.2 175 97.2 3.15 80.0 30 16.7 0.54 13.7 80 44.4 1.44 36.6 130 72.2 2.34 59.4 180 100.0 3.24 82.3 35 19.4 0.63 16.0 85 47.2 1.53 38.9 135 75.0 2.43 61.7 185 102.8 3.33 84.6 40 22.2 0.72 18.3 90 50.0 1.62 41.1 140 77.8 2.52 64.0 190 105.6 3.42 86.9
26、 45 25.0 0.81 20.6 95 52.8 1.71 43.4 145 80.6 2.61 66.3 195 108.3 3.51 89.2 50 27.8 0.90 22.9 100 55.6 1.80 45.7 150 83.3 2.70 68.6 200 111.1 3.60 91.4 For conduit installed outdoors, the maximum and minimum air temperature expected can be used to calculate the range of expansion and contraction. Co
27、nduit installed outdoors in direct sunlight will be considerably hotter than air temperature during the day because of the absorption of the suns heat. Expansion fittings should be installed to allow for the anticipated temperature change. For direct sunlight exposure, add 30F or 16.7C to ambient ai
28、r temperature change. Where installed inside buildings, the conduit temperature is the ambient air temperature plus the heat contributed by the conductors inside the conduit. Generally, expansion fittings are not required inside unless conduit is located in an area of widely varying temperatures. At
29、tics of buildings are areas where temperature swings exceeding 100F or 55.6C are common and expansion fittings are required. NEMA PRP 3-2009 (R2016) Page 3 2016 National Electrical Manufacturers Association Note: Add 30F or 16.7C to temperature change for direct sunlight exposure. Proper Position Ex
30、pansion fittings are usually installed in a horizontal position. However, if they must be put in a vertical application, the open end should be securely fastened in the down position. The expansion fitting must be installed close to the top of the run with the barrel pointing down, so that rain wate
31、r does not enter into the opening. To further reduce likelihood of the infiltration of water or debris into the fitting, the use of an O-ring expansion joint is recommended. The lower end of the conduit run should be secured at the bottom. This will result in an upward movement due to the length cha
32、nge caused by temperature variations. Setting Position of Piston If an expansion fitting was installed completely closed with the piston bottomed on a cool day, there would be no travel available when the conduit warmed up and expanded. If it was installed in a maximum open position on a hot day, th
33、e expansion fitting would pull apart when cooled. Thus, “setting” the expansion fitting is very important. Length of Run Expansion Allowance Needed for Temperature Changes of: ft m 60F in 33C mm 80F in 44C mm 100F in 56C mm 120F in 67C mm 140F in 78C mm 25 8 6 10 13 16 19 50 15 16 19 1 25 1 29 1 32
34、75 23 22 1 29 1 35 1 41 2 51 100 31 1 29 1 38 1 48 2 57 2 67 125 38 1 35 1 48 2 57 2 70 3 83 150 45 1 41 2 57 2 70 3 83 3 98 (60.96 m) (60.96 m) (60.96 m) (60.96 m) Intermediate Hanger Anchoring Hanger with Split Stop Ring O-Ring Expansion joint NEMA PRP 3-2009 (R2016) Page 4 2016 National Electrica
35、l Manufacturers Association In addition to the proper number and sizes of expansion fittings chosen, they must also be installed so they can accommodate the expected length change. This requires proper “setting” of the expansion fitting. Most will be installed at a temperature halfway between maximu
36、m and minimum; for example, installation at 65F or 18.3C with an anticipated maximum temperature of 125F or 51.6C and a minimum of 5F or 15C. In this case, the expansion fitting would be installed or “set” with the inner piston halfway out. Expansion fittings are marked with a mid-point ring. If it
37、was a colder day, for example 35F or 2C, with the same expected temperature change range; the inner piston would be set with of its maximum travel out. If the temperature was hot 95F or 35C, it would be set with the inner piston only ” or 6 mm of the way out (unless otherwise specified by the manufa
38、cturer). Setting Expansion Fitting for Temperature When a more precise calculation for expansion is needed, it can be made as follows: 1. You must determine the maximum temperature range. This is done by subtracting the lowest temperature you anticipate from the highest temperature you anticipate. E
39、xample: Lets say in winter, we expect the temperature to get down to 10F or 23C and in the summer, we expect the temperature to get as high as 110F or 43C. The maximum temperature range is 110 (10) = 120F or 43 (23) = 66C. 3/43/41/2 1/41/4 1/2 MAX3/4 1/2 1/43/41/21/4 MAX3/4 1/2 1/41/4 1/2 3/4 MAXB.
40、For ambient temperature (65 to 75 F or 18 to 24 C) set piston way out of the barrel. A. For cold temperature (20 to 30 F or 7 to 1 C) set piston way out of the barrel. C. For hot temperature (95 to 105 F or 35 to 41 C) set piston way out of the barrel. NEMA PRP 3-2009 (R2016) Page 5 2016 National El
41、ectrical Manufacturers Association 2. The length of run between fixed points must be determined. Assume 90 feet or 27.4 m for this example. 3. The total expansion change can be calculated as follows: Total expansion change in inches = (coefficient of thermal expansion) (maximum temperature range in
42、F) (length of run in inches). Example: Total expansion change = (1.5 10-5in./in./F) (120F) (90ft 12in./ft) = 1.95 in. Total expansion change in mm = (coefficient of thermal expansion) (maximum temperature range in C) (length of run in mm). Example: Total expansion change = (2.7 10-5 mm/mm/C) (66C) (
43、27.4m 1000mm/m) = 48.8 mm. 4. The “set position” can be determined from the following example. Example: If the temperature at installation was 65F or 18C, the difference from maximum is 110F 65F = 45F or 25C. Use ratio: (difference from maximum)/(Total expected range) = 45/120 = 0.375 (25/66 = 0.379
44、). 0.375 1.95 inch travel = 0.73 in. or 0.379 48.8 = 18.5 mm. The piston at 65F or 18C would retract 0.73 inches or 18.5 mm. Installation 1. The O-ring expansion fitting should be mounted so that the piston can travel in a straight line with the barrel. If alignment is not straight, the piston will
45、bind and prevent the fitting from working properly. 2. The O-ring expansion fitting barrel must be clamped securely whereas the conduit is mounted loosely so that it can slide freely during expansion and contraction. 3. Nonmetallic conduit straps suitable for this purpose must be used to allow the c
46、onduit to move freely during expansion and contraction while properly supporting it. NEMA PRP 3-2009 (R2016) Page 6 2016 National Electrical Manufacturers Association Location Proper placement and installation of expansion fittings and conduit allow for correct functioning of the expansion fittings.
47、 For example, if one expansion fitting is needed between two boxes, abutments or vaults, the barrel of the fitting must be securely fastened close to one box. The conduit must be loosely supported so as to allow for movement during expansion and contraction. If there is more than one O-ring expansio
48、n fitting used, then fittings are installed at the boxes with the center of the conduit run rigidly fixed. With two expansion fittings utilized, the center of the conduit must be fixed so as to properly proportion expansion or contraction between the two fittings. Otherwise, the expansion or contraction would only occur at the free fitting, while the tighter fitting would not move. In a long run, two or more fittings should be placed in series in a back-to-back configuration with one another. The barrel of each expansion fitting m
