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The Chapter Three wiring methods include various cable types, such as:
1. Armored Cable (Type AC) [320].
2. Metal Clad Cable (Type MC) [330].
3. Nonmetallic-Sheathed Cable (Types NM and NMC) [334].
4. Power and Control Tray Cable: Type TC [336].
5. Service-Entrance Cable: Types SE and USE [338].
Armored Cable is an assembly of insulated conductors, 14 AWG through 1 AWG, individually wrapped within waxed paper and contained within a flexible spiral, interlocked metal armor with an internal bonding strip in intimate contact with the armor for its entire length.
Metal-Clad Cable (Type MC) is a factory assembly of insulated circuit conductors, with or without optical fiber members, enclosed in an armor of interlocking metal tape (or metallic sheath) [330.2]. Because the outer sheath of traditional interlocked Type MC cable isn’t listed as an equipment grounding conductor [250.118(10)a.], Type MC contains an equipment grounding conductor [330.108]. There is a Type MC cable (Type MCAP ® is one example) where the metallic sheath is combined with a bare equipment grounding conductor (EGC) that does qualify the cable as an EGC [250.118(10)b.]. Figure 01
Nonmetallic-Sheathed Cable (Types NM and NMC) encloses two or more insulated conductors, 14 AWG through 2 AWG, within a nonmetallic jacket [334.2]. NM cable has insulated conductors enclosed within an overall nonmetallic jacket. The jacket of Type NMC cable is also corrosion-resistant.
Power and Control Tray Cable (Type TC) is a factory assembly of two or more insulated conductors under a nonmetallic jacket [336.2].
Service-Entrance Cable is a single or multiconductor assembly, with or without an overall covering, used primarily for services [338.2]. Type SE and SER cables have a flame-retardant, moisture-resistant covering. SER cable has an insulated neutral (resulting in three insulated conductors) with an uninsulated equipment grounding conductor. SER cable is round, while 2-wire SE cable is flat. Type USE cable is for underground applications; its covering is moisture resistant, but not flame retardant.
Uses
You can use Type AC cable for [320.10]:
(1) Feeders and branch circuits in exposed or concealed installations.
(2) Cable trays.
(3) Dry locations.
(4) Embedding in plaster or brick, except in damp or wet locations.
(5) Air voids where not exposed to excessive moisture or dampness.
And you can install Type AC cable in a plenum space where listed for use in an air-handling space [300.22(C)(1)].
But you can’t use it [320.12]:
(1) Where subject to physical damage.
(2) In damp or wet locations.
(3) In air voids of masonry block or tile walls where such walls are exposed or subject to excessive moisture or dampness.
(4) Where exposed to corrosive conditions.
The general uses for Metal Clad Cable (Type MC) [330.10(A)]:
(1) In branch circuits, feeders, and services.
(2) In power, lighting, control, and signal circuits.
(3) Indoors or outdoors.
(4) Exposed or concealed.
(5) Directly buried if identified for the purpose.
(6) In a cable tray.
(7) In a raceway.
(8) As aerial cable on a messenger.
(9) In hazardous locations as permitted in 501.10(B), 502.10(B), and 503.10.
(10) Embedded in plaster or brick in dry locations.
(11) In wet locations, where a corrosion-resistant jacket is provided over the metal sheath and any of the following are met:
a. The metallic covering is impervious to moisture.
b. A jacket is provided under the metal covering that’s moisture resistant.
c. The insulated conductors under the metallic covering are listed for use in wet locations.
(12) If single-conductor cables are used, all circuit conductors must be grouped together to minimize induced voltage on the sheath [300.3(B)].
Specific uses for Type MC [330.10(B)].
(1) In a cable tray per Article 392.
(2) Direct Buried (cables must be protected per 300.50).
(3) Installed as service-entrance cable (if installed per 230.43).
(4) Installed outside of buildings; it must comply with 225.10, 396.10, and 396.12.
But you can’t use it where [330.12]:
(1) Subject to physical damage.
(2) Exposed to the destructive corrosive conditions in (a) or (b), unless the metallic sheath or armor is resistant to the conditions (or protected by material resistant to the conditions):
a. Direct burial in the earth or embedded in concrete unless identified for the application.
b. Exposed to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids.
You can use Type NM and Type NMC cables for [334.10]:
(1) One- and two-family dwellings of any height, and their attached/detached garages or storage buildings.
(2) Multifamily dwellings permitted to be of Types III, IV, and V construction. See Annex E for the determination of building types [NFPA 220, Table 3-1].
(3) Other structures permitted to be of Types III, IV, and V construction. Cables must be concealed within walls, floors, or ceilings that provide a thermal barrier of material with at least a 15-minute finish rating, as identified in listings of fire-rated assemblies.
But you can’t use Types NM or NMC cables [334.12(A)]:
(1) In any dwelling or structure not specifically permitted in 334.10(1), (2), (3), and (5).
(2) Exposed within a dropped or suspended ceiling cavity in other than one and two family, and multifamily dwellings.
(3) As service entrance cable.
(4) In commercial garages having hazardous locations, as defined in 511.3.
(5) In theaters and similar locations, except where permitted in 518.4(B).
(6) In motion picture studios.
(7) In storage battery rooms.
(8) In hoistways, or on elevators or escalators.
(9) Embedded in poured cement, concrete, or aggregate.
(10) In any hazardous location, except where permitted by other sections in the Code.
And you can’t use Type NM cables:
(1) If exposed to corrosive fumes or vapors.
(2) If embedded in masonry, concrete, adobe, fill, or plaster.
(3) In a shallow chase in masonry, concrete, or adobe and covered with plaster, adobe, or similar finish.
(4) In wet or damp locations. A raceway in a ground floor slab is considered a wet location [300.5(B)].
You can use Power and Control Tray Cable (Type TC) in [336.10]:
(1) Power, lighting, control, and signal circuits.
(2) Cable trays including those with mechanically discontinuous segments up to 1 ft.
(3) Raceways.
(4) Outdoor locations supported by a messenger wire.
(5) Class 1 circuits as permitted in Parts II and III of Article 725.
(6) Nonpower limited fire alarm circuits per 760.49.
(7) Between a cable tray and equipment if it complies with 336(10)(7) a. through f.
(8) Wet locations where the cable is resistant to moisture and corrosive agents.
(9) One and two family dwellings, Type TC ER cable is permitted per Part II of Article 334.
(10) Direct buried where identified for direct burial.
But you can’t use Type TC cables [336.12]:
(1) Where exposed to physical damage
(2) Outside a raceway or cable tray system, except as permitted in 336.10(4), 336.10(7), 336.10(9), and 336.10(10)
(3) Exposed to direct rays of the sun, unless identified as sunlight resistant.
You can use Service-Entrance Cable as [338.10]:
• Service entrance conductors, if installed per Article 230.
• Branch circuits and feeders, where the circuit conductors are insulated.
SE cable is permitted for branch circuits and feeders if the insulated conductors are used for circuit wiring, and the uninsulated conductor is used only for equipment grounding. Ex: In existing installations, uninsulated conductors may be used for the neutral conductor if the uninsulated neutral conductor of the cable originates in service equipment.
SE cable used for branch circuits or feeders must comply with 338.10(B)(4)(a) and (b).
(a) Interior Installations. Install per the same requirements as Type NM Cable—Article 334, excluding 334.80.
Where installed in thermal insulation, the ampacity of conductors 10 AWG and smaller, must be sized with the 60°C (140°F) conductor temperature rating per Table 310.15(B)(16). For conductor ampacity correction and/or adjustment, use the conductor temperature rating ampacity.
(b) Exterior Installations. Support the cable per 334.30. Where run underground, the cable must comply with Part II of Article 340.
You can’t use SE cable [338.12(A)]:
(1) If subject to physical damage unless protected in accordance with 230.50(B).
(2) Underground with or without a raceway.
You can’t use USE cable [338.12(B)]:
(1) For interior wiring.
(2) Above ground, except where protected against physical damage per 300.5(D).
Review your selection
You can see there are many differences in permitted and prohibited uses. Being familiar with these helps you select the correct cable for the application. Once you’ve done that, address the NEC’s installation requirements for the cable you’ve chosen. At this point, you still have many steps left to complete the job. To avoid doing them over, review your cable selection before proceeding with them.
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