NOTE: See Section 6 for PVC-coated conduit
Size and raceway type
Before installing a fitting or a raceway support, review the packaging labels containing specific applications for which the fitting or raceway support is recommended and / or listed.
NOTE: Do not take applications for granted. Many fitting designs look the same but may contain subtle construction differences designed to enhance performance in particular applications. Listed fittings contain required, informative markings and any specific conditions for use. For specific selection and installation guidelines, consult NEMA FB2.10, “Selection and Installation Guidelines for Fittings for Use with Nonflexible Metallic Conduit and Tubing.”
Fittings and raceway supports shall be used only with conduit of the trade size indicated on the fitting or raceway support or its smallest unit shipping container.
Fittings for special applications
Threadless fittings intended for use in wet locations are marked “Wet locations” on the fitting or its smallest unit shipping container. Fittings marked “Raintight” are suitable for use in “Wet Locations.” ”Wet Locations” fittings are sometimes referred to as “Raintight.”
A threadless fitting designed for use in wet locations that requires a gasket or sealing ring installed between the fitting and a box shall be installed only with the specific component marked on the fitting’s smallest unit shipping container.
NOTE: “Wet Locations” or “Liquidtight” fittings are not necessarily suitable for use in applications where submersion in water is expected. ”Wet Locations” fittings are not necessarily considered “Liquidtight.” “Liquidtight” fittings are intended for use in typical wet locations and also in “wet” industrial environments which may contain machine oils and coolants.
RMC and IMC fittings for use in industrial applications involving sprayed mineral oils and coolants are marked “Liquidtight” on the fitting or its smallest unit shipping container. Threadless fittings intended for embedment in poured concrete are marked “Concrete-tight” or “Concrete-tight when taped” or ”Wet Locations” on the fitting’s smallest unit shipping container.
NOTE: Taping is adequate to prevent the entrance of concrete aggregate into the raceway or box. Concrete aggregate consists of cement combined with inert material such as coarse sand. When hardened, such aggregate may be abrasive and might pose a risk of abrading conductor insulation or effectively reducing the area inside the raceway. Fittings listed as ”Wet Locations” are also “Concrete-tight.” The term “Raintight” has been removed from UL 514B as the result of NEC® changes that removed the term in reference to EMT and rigid fittings. The term “Wet Locations” is now required.
Expansion and deflection fittings
Expansion fittings shall be installed where significant temperature differentials are anticipated. When conduit is installed as outdoor raceway spans between buildings, attached to bridges, on rooftops, etc., where expansion and contraction would result from the direct heat of the sun coupled with significant temperature drops at night, the full coefficient of expansion shall be applied in determining the need for expansion fittings. Table 3 shows length changes for steel conduit and tubing at selected temperature differentials.
NOTE: Where the conduit is not exposed to the direct heat of the sun, expansion fittings are not generally necessary, because the coefficients of expansion for steel and common building materials are so similar. In conduit or tubing runs where expansion fittings are installed, provision shall be made for the raceway to slide through the supports so that, when expansion or contraction occurs, it will allow the fitting to open and close properly. One way to accomplish this is to place a short sleeve over the raceway at each support large enough to allow the raceway to move freely with normal expansion and size support clamps to the sleeve size.
Strong consideration should be given to the use of deflection fittings or other approved means when crossing a construction joint used in buildings, bridges, parking garages, or other structures. Structural construction joints will experience shear and lateral loads due to gravity, expansion and contraction, and movement of the structure. Where significant expansion is expected, expansion fittings can be installed in-line with a deflection fitting, or a combination expansion / deflection fitting can be used.
Threadless fittings shall not be assembled to threaded RMC or IMC unless specifically recommended by the fitting manufacturer. Where threadless fittings are to be assembled to steel RMC, IMC and EMT, conduit ends shall:
- have squarely cut ends, free of internal and external burrs, and circular form as provided from the factory,
- be free from dirt or foreign matter on the surface of the conduit to be inserted into the fitting, and
- have the ends of the conduit or tubing assembled flush against the fitting’s end stop. Careful consideration shall be given to the torque applied to the fitting’s securement means.
|Table 3: Expansion Characteristics of Steel Conduit and Tubing
Coefficient of Thermal Expansion = 0.65 x 10-5in./in./°F*
|Temperature Changes in |
|Length Change Steel Conduit |
|Temperature Changes in |
|Length Change Steel Conduit|
|Temperature Changes in|
|Length Change Steel Conduit|
|Length Change Steel Conduit
* A Fine Print Note in Section 300.7(B) of the NEC refers the user to the Expansion Characteristics of PVC, Table 352.44(A) for Rigid Nonmetallic Conduit and suggests multiplying the lengths in that table by 0.20 in order to obtain a nominal number for steel conduit. Since the coefficient of steel conduit is between 2–3 times less than that of PVC conduit you would need more expansion fittings for PVC conduit for a given temperature and length than for steel conduit. We have used the coefficient of expansion of steel, rather than the 0.20 multiplier, to calculate the exact length of change figures in Table 3.
NOTE: Listed fittings are tested under prescribed torque, which represents normal, not excessive force. Performance is not enhanced, and can be reduced, by over- torqueing the fitting’s securement means.
The length of screws provided with set-screw type fittings varies. The appropriate torque for some designs is reached when the head of the screw touches a screw boss on the fitting. This cannot be universally relied upon, however. Screws on certain fitting designs, particularly larger trade sizes, can offer more than one tightening option including screwdriver (Slot, Phillips, or Robertson-square drive) and bolt head for wrench application (hex or square). Greater mechanical advantage and torque can generally be achieved with a wrench. Where tightening options for both screwdriver and wrench application are offered, torque should be limited to that which can be applied by the screwdriver.
Compression (gland) type
Generally, most compression gland nuts achieve maximum securement after hand tightening and then wrench tightening one or two additional turns.
Prior to embedment in poured concrete, all threadless fittings, including those marked “Concrete-tight,” shall be taped adequately to prevent the entrance of concrete aggregate where they will be embedded more than 24 inches or where the pour area will be subjected to a concrete vibrator. Tape shall be applied after the fitting is assembled and secured to the conduit.
Threaded joints, both fitting to conduit and fitting to threaded integral box entries, shall be made up wrench tight.
NOTE: Avoid excessive force. Generally a force equivalent to hand tight plus one full turn with an appropriate tool is recommended. This should ensure engagement of at least three full threads.
Conduit bodies generally have an integral bushing to provide a smooth surface for conductors when pulled. This bushing is often mistaken for a conduit end stop. It is not necessary that the conduit be inserted flush against this bushing to assure a secure joint.
Attachment to boxes and support
Prior to attachment to a box, enclosure or a threadless coupling, RMC, IMC and EMT shall be supported at intervals required by the NEC, using raceway supports intended for the purpose and secured by hardware acceptable to the local jurisdiction.
NOTE: The variability of mounting surfaces, expected loads, and application environments will determine the appropriate support options and securement hardware. Project specifications normally calculate support requirements based on the minimum spacing intervals given in the NEC. Using closer support intervals than are required by the NEC is an acceptable option for heavier supports and mounting hardware in some applications.
Properly align the raceway, fittings and knockouts to provide secure mechanical and electrical connections. Allow sufficient conduit length to complete engagement of the conduit and fittings at joints and entries.
Conduit bushings shall not be used to secure threaded RMC or IMC to a box or enclosure. A locknut shall always be assembled between a conduit bushing and the inside of the box or enclosure.
EMT connectors are permitted to be assembled into threaded entries of boxes, conduit bodies or internally threaded fittings having tapered threads (NPT). EMT fittings designed to NEMA FB 1, “Fittings, Cast Metal Boxes, and Conduit Bodies for Conduit and Cable Assemblies,” have straight threads (NPS). Threaded openings where these fittings are intended to be used are permitted to have either tapered (NPT) or straight (NPS) threads. Care should be taken to ensure that the threaded entry will accommodate a minimum of three full engaged threads of the fitting.
Where a locknut is provided with a fitting as the means of securement to a box or enclosure, the locknut is to be secured by hand-tightening to the enclosure plus 1/4 turn using an appropriate tool.
NOTE: While securing the locknut, take care to avoid excessive pressure when gripping the body of the fitting is necessary.
Do not rely upon locknuts to penetrate nonconductive coatings on enclosures. Coatings shall be removed in the locknut contact area prior to raceway assembly to ensure that a continuous ground path is achieved. Touch up bare area as needed after installation.
Verification of installation
After the raceway is fully installed and supported, and prior to installing conductors in the raceway, all fittings and locknuts shall be re-examined for secureness (see 5.5).