Cable and Wiring Methods
The same conductor size can be installed in very different ways. A wire pulled through conduit, a factory-assembled cable, an armored cable, and a flexible cord are different wiring methods with different listings and code rules.
Individual conductors in raceway
THHN/THWN-2 and XHHW-2 are common examples of individually insulated conductors used in raceways when their complete markings suit the location. Raceway installations require attention to fill, conductor grouping, pulling tension, bends, fittings, grounding, wet locations, and physical protection.
NM-B cable
Nonmetallic-sheathed cable, commonly called NM-B and often referred to by the brand name Romex, combines insulated circuit conductors and an equipment grounding conductor inside a nonmetallic jacket. It is widely used in residential construction where the NEC permits it.
UF cable
Underground feeder cable is made for applications that can include wet locations and direct burial when the particular product and installation are listed and permitted for that use. It is more moisture-resistant than ordinary NM cable and usually has a solid or closely molded overall construction.
MC cable
Metal-clad cable contains insulated conductors inside metallic armor. Different MC cable products are made for dry, wet, hazardous, healthcare, fire-alarm, feeder, and other applications. The marking on the actual product matters; “MC” alone does not tell every permitted use.
Service-entrance and feeder cable
Service-entrance cable and other feeder cable assemblies are designed around particular service and feeder applications. Their conductor materials, jackets, neutral construction, insulation, and permitted locations vary. Large aluminum conductors are common in this category.
Tray cable
Tray cable is a multi-conductor cable family intended for cable tray and other permitted applications. Some products carry additional markings for exposed run, direct burial, sunlight resistance, or wet locations. Again, the complete marking and listing control.
Raceway is not “just pipe”
Electrical metallic tubing, rigid metal conduit, PVC conduit, flexible raceways, and other raceways provide different degrees of mechanical, environmental, and grounding performance. The raceway itself may form part of the equipment grounding path when permitted, or an equipment grounding conductor may also be installed.
Conduit fill
Raceways need space so conductors can be installed without damage and can dissipate heat. NEC Chapter 9 tables are used with raceway and conductor dimensions to determine permitted fill. Fill rules depend on how many conductors or cables occupy the raceway.
Current-carrying conductors together
Bundling or placing many loaded conductors together can trap heat. The NEC therefore includes ampacity adjustment rules for multiple current-carrying conductors in a raceway, cable, or bundle under specified conditions. Neutral-conductor treatment depends on the circuit and load.
Manufacturer markings matter
A cable jacket may identify conductor size, number of conductors, voltage, temperature, wet/dry suitability, sunlight resistance, oil resistance, direct burial, flame rating, manufacturer, listing marks, and other properties. Learning to read the printing on the cable is one of the fastest ways to avoid guessing.