The installation of Rigid Steel Conduit (RSC) is covered by Article 344 of the National Electrical Code® (NEC®). This article is entitled "Rigid Metal Conduit (RMC) and includes all requirements for all rigid metal conduits, including steel, stainless steel, aluminum, and red brass. Information on this STI website covers only rigid steel conduit. You will often see the following acronyms used: RSC (Rigid Steel Conduit), ERSC (Electrical Rigid Steel Conduit), or GRC (Galvanized Rigid Conduit) in place of RMC (Rigid Metal Conduit) in order to differentiate the type of metal used in the product.
Rigid steel conduit (RSC) 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. 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. Rigid metal conduit is available in trade sizes 1/2 through 6. Thread protectors for trade sizes 1, 2, 3, 4, 5, and 6 are color-coded blue, trade sizes 1/2, 1 1/2, 2 1/2, 3 1/2 are black, and trade sizes 3/4 and 1-1/4 are red. The nominal finished length of RMC with couplings is 10 feet. Twenty foot lengths are available in some trade sizes.
There are different processes used to provide corrosion protection to rigid steel conduit. Rigid steel conduit 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.
Rigid steel conduit is the heaviest-weight and thickest wall conduit. Where galvanized by the hot-dip process, it has a coating of zinc on both the inside and outside. Electro-galvanized rigid conduit has a coating of zinc on the exterior only, with approved corrosion resistant organic coatings on the interior. Rigid conduit with "alternate corrosion protection coatings" generally has organic coatings on both the exterior and the interior surfaces. Galvanized rigid metal conduit (GRC) is non-combustible and can be used indoors, outdoors, underground, concealed or exposed. Rigid steel conduit with coatings that are not zinc-based may have temperature limitations which will be noted on the manufacturer's product label and may not be listed for use in environmental air spaces; consult manufacturers’ listings and markings.
Intermediate Metal Conduit — (IMC STEEL CONDUIT)
The product was developed in the 1970s. Intermediate Metal Conduit (IMC) is a lighter-weight, thinner wall alternative to rigid steel conduit. Covered under Article 342 in the NEC®, IMC is a listed threaded steel raceway of circular cross section with a coupling which can be either a standard straight-tapped conduit coupling or the integral type. 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. IMC is available in trade sizes 1/2 through 4. Thread protectors for trade sizes 1, 2, 3, 4, are color-coded orange; trade sizes 1/2, 1 1/2, 2 1/2, 3 1/2 are yellow; and trade sizes 3/4 and 1 1/4 are green. The nominal finished length of IMC with coupling is 10 feet.
IMC has a reduced wall thickness, when compared to RSC, and weighs about one-third less than RSC. The outside has a galvanized coating for corrosion protection and the inside has an approved organic corrosion-resistant coating. IMC is interchangeable with galvanized rigid steel conduit. Both have threads with a 3/4-inch per foot taper, use the same couplings and fittings; have the same support requirements; and are permitted to be used in the same locations.Electrical Metallic Tubing — (EMT STEEL CONDUIT)
Electrical Metallic Tubing (EMT), also commonly called thin-wall, is a listed steel raceway of circular cross section which is unthreaded, and nominally 10 feet long. Twenty foot lengths are also available. Covered by Article 358 of the NEC®, EMT is available in trade sizes 1/2 through 4. The outside is galvanized for corrosion protection and the inside has an approved corrosion resistant organic coating. EMT is installed by use of set-screw or compression-type couplings and connectors. It is permitted to have an integral coupling which is comprised of an expanded, "belled" shape of tube on one end with set screws. EMT with integral couplings is available in trade sizes 2 through 4.
Steel conduits are manufactured to specifications defined by the British Standards Institute (BS).
Class 4 conduit has a hot dip galvanized finish. It is of heavy gauge with a welded seam. This conduit is suitable for use in external or damp installations.This is the conduit most widely used in this country.
Also manufactured is a solid drawn seamless conduit which is more expensive and only used for special gas tight, explosion proof or flame proof installations.
Conduit is normally supplied in 3 or 3.75 metre lengths and typical conduit external diameters are 16, 20, 25 and 32mm.
· Affords cables good mechanical protection
· Permits easy rewiring
· Minimises fire risks.
· Some Disadvantages of Steel Conduit
· Under certain conditions moisture is liable to form on the inside wall of the conduit.
· Expensive compared with some other wiring systems.
Ống thép luồn dây điện BS4568-BS31 JISC8305-ống ruột gà lõi thép luồn dây điện Ống thép luồn dây điện EMT steel conduit (Electrical Metallic Tubing), ống thép mạ kẽm luồn dây điện ren 2 đầu IMC steel conduit (Intermediate Metal Conduit), ống thép tráng kẽm luồn dây điện ren RSC steel conduit (Rigid Steel Conduit), ống luồn dây điện tiêu chuẩn Nhật Loại E & C, ống thép GI – STK luồn cáp quang/cáp điện tiêu chuẩn BS4568-BS31, ống thép luồn dây điện mềm, ống ruột gà thép KAIPHONE-CVL, ống ruột gà lõi thép mạ kẽm luồn dây điện, ống luồn dây điện mềm
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