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ARTICLE 334 Nonmetallic-Sheathed Cable: Types NM and NMC
Nonmetallic-sheathed cable is flexible, inexpensive, and easily installed and is a common wiring method used for residential and commercial branch circuits. It provides very limited physical protection of the conductors, so the installation restrictions are strict. However, its low cost and relative ease of installation make it a common wiring method used for residential and commercial branch circuits.
ARTICLE 348 Flexible Metal Conduit: Type FMC
Flexible metal conduit, commonly called Greenfield or simply "flex," is a raceway of interlocked metal strip of either steel or aluminum. It's primarily used for the final 6 ft or less of raceway between a more rigid raceway system and equipment that moves, shakes, or vibrates. Examples of such equipment include pump motors and industrial machinery.
ARTICLE 350 Liquidtight Flexible Metal Conduit: Type LFMC
Liquidtight flexible metal conduit, with its associated connectors and fittings, is a flexible raceway system commonly used for connections to equipment that vibrate or are required to move occasionally. Liquidtight flexible metal conduit is commonly called Sealtight® or simply "liquidtight." Liquidtight flexible metal conduit is of similar construction to flexible metal conduit, but has an outer liquidtight thermoplastic covering. It has the same primary purpose as flexible metal conduit, but it also provides protection from moisture and corrosive effects.
ARTICLE 353 High-Density Polyethylene Conduit: Type HDPE
This is a new article in the 2005 NEC. This type of conduit has been in use in the United Kingdom for a long time. It's lightweight and durable. It resists decomposition, oxidation, and hostile elements that cause damage to other materials. It is mechanically and chemically resistant to a host of environmental conditions. Uses include communication, data, cable television, and general-purpose raceways.
Author's Comment: High-density polyethylene conduit can be used in continuous lengths in almost all outside underground locations. However, this product has different properties than rigid nonmetallic conduit, therefore it has its own article.
ARTICLE 376 Metal Wireways
A metal wireway or "trough" is commonly used where access to the conductors within the raceway is required to make terminations, splices, or taps to several devices at a single location. Its cost precludes its use for other than short distances, except in some commercial or industrial occupancy where the wiring is frequently revised.
ARTICLE 386 Surface Metal Raceways
A surface metal raceway is a common method of adding a raceway when exposed conduit systems are not esthetically acceptable and concealing the raceway is not economically feasible. It comes in several colors, and now is available with colored or real wood inserts designed to make it look like molding rather than raceway.
ARTICLE 388 Surface Nonmetallic Raceways
A surface nonmetallic raceway is a common method of adding a raceway when exposed conduit systems are not esthetically acceptable and concealing the raceway is not economically feasible. Surface nonmetallic raceway is less expensive than comparable surface metallic raceway and more easily installed, but may not be as impact resistant. However, it does not dent, deform, or loose paint like the metallic versions, so it may retain its appearance longer.
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