Steel Conduit Info for Electrical Fittings

Steel conduit has been in use as a raceway system for electrical conductors since the early 1900s. The wall thickness and strength of steel make metal conduit the wiring method recognized as providing the most mechanical protection to the enclosed conductors. An additional benefit of using steel conduit is that the NEC recognizes a properly installed metal.

Steel Conduit Electrical Fittings

 

The Cost Advantage of Steel Conduit

The ability to future proof the electrical system by using steel conduit lowers the total cost of the system during its life span. Today, the need to replace or upgrade power, data and communications circuits can happen overnight. Requirements for more sophisticated electronic equipment, increased power requirements or new applications can cause owners and tenants to demand changes in the wiring of their plants, retail complexes or buildings. Steel conduit is adaptable and can accommodate these changes, making it easier to pull out old wiring and install new systems. Steel conduit also provides the quickest and most efficient changeover or upgrading of electrical conductors. It all adds up to make steel conduit the most cost-effective wiring method over time — and this is only one of the many benefits steel conduit provides.

Steel conduit has been in use as a “raceway system” for electrical conductors since the early 1900s. The wall thickness and strength of steel make metal conduit the wiring method recognized as providing the most mechanical protection to the enclosed conductors. An additional benefit of using steel conduit is that the NEC recognizes a properly installed metal conduit system as an equipment grounding conductor.

Three basic types of steel conduit are in use today: rigid metal conduit, intermediate metal conduit, and electrical metallic tubing. Let’s take a closer look at the features of each type.
Rigid metal conduit — RMC (ferrous metal). RMC is a listed threaded metal raceway of circular cross section with a coupling, which can be either a standard straight tapped conduit coupling or the integral type (Photo 1). Threads on the uncoupled end are covered by industry color-coded thread protectors, which protect the threads, keep them clean and sharp, and aid in trade size recognition. RMC is available in trade sizes ½ through 6. (See the Table for metric trade size designators.) Thread protectors for trade sizes 1, 2, 3, 4, 5, and 6 are color-coded blue; trade sizes ½, 1½, 2½, and 3½ are black; and trade sizes ¾ and 1¼ are red. The standard finished length of RMC with coupling is 10 feet.
RMC can have a primary coating of zinc, a combination of zinc and organic coatings, or a nonmetallic coating, such as PVC. Supplementary coatings can be applied to all three where additional corrosion protection is needed.
RMC is the heaviest-weight and thickest-wall steel conduit. Where galvanized by the hot-dip process, it has a coating of zinc on both the inside and outside. Electro-galvanized RMC has a coating of zinc on the exterior only, with approved corrosion-resistant organic coatings on the interior. RMC with alternate corrosion protection generally has organic coatings on both the exterior and the interior surfaces. Galvanized RMC is noncombustible and can be used indoors, outdoors, underground, concealed or exposed. RMC with non-zinc-based coatings may have temperature limitations that will be noted on the manufacturer’s product label and may not be listed for use in environmental air spaces; consult the manufacturer’s listings and markings.

Steel Conduit Fittings

Applications

There are two primary reasons to use steel conduit. It’s the best possible protection of your electrical conductor and wiring systems, and it facilitates the insertion and extraction for conductors and wiring. Today, steel conduit is used in virtually every application where electrical conduit and wiring is present: commercial, retail and residential buildings, manufacturing and other industrial facilities, health-care, educational and other institutions, and a wide variety of indoor, outdoor, and underground applications, even where corrosive and hazardous conditions exist.
RMC has the thickest wall, which makes it the heaviest steel conduit. It can be used indoors, outdoors, underground, and in both concealed and exposed applications.
IMC has a thinner wall and weighs less than RMC.
IMC can be used for the same applications as galvanized RMC.EMT is the lightest-weight steel conduit manufactured. Field workers typically find it easy to alter, reuse, or redirect EMT. Even though EMT is made of lighter-walled steel, it still provides substantial physical protection and can be used in most exposed locations, except where severe physical damage is a possibility.

Electrical Fittings for Steel Conduit

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 lookthe same but may contain subtle construction differences designed to enhance performance in particular applications. Listed fittingscontain required, informative markings and any specific conditions foruse. 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 the 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 an inert material such as coarse sand. When hardened, such aggregate may be abrasive and might pose a risk to abrade conductor insulation or effectively reduce 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.)

Threadless (No Threads NT or Compression Fittings

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:
a. have squarely cut ends, free of internal and external burrs, and circular form as provided from the factory,
b. be free from dirt or foreign matter on the surface of the conduit to be inserted into the fitting, and
c. 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 securementmeans.
⇒ (NOTE: Listed fittings are tested under prescribed torque which represents normal, not excessive force. Performance is not enhanced, and can be reduced, by over- torquing the fitting’s securement means.)

 Set-Screw (SS or SNT) Type

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.

Threaded Fittings

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 assure 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.

Read More. . .  Steel Institute Guidelines for Installing Steel Conduit →

View American Fittings Steel Electrical Fittings Products →

 


The information presented in this article was adapted from source material provided by the Steel Tube Institute of North America (www.steelconduit.org ) and E C M by. Mike Ebbie, Editor and Chief

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