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National Electric Codes > Article 334 - Metal Clad Cable

Article 334 - Metal-Clad Cable

Type MC

A. General

•334-1. Definition. Type MC cable is a factory assembly of one or more insulated circuit conductors with or without optical-fiber members enclosed in a metallic sheath of interlocking tape, or a smooth or corrugated tube.

•334-2. Other Articles. Metal-clad cable shall comply with this article and also with the applicable provisions of other articles in this Code, especially Article 300. Type MC cable shall be permitted for systems in excess of 600 volts, nominal. See Section 300-2(a).

•334-3. Uses Permitted. Except where otherwise specified in this Code and where not subject to physical damage, Type MC cables shall be permitted as follows:

  1. For services, feeders, and branch circuits;
  2. For power, lighting, control, and signal circuits;
  3. Indoors or outdoors;
  4. Where exposed or concealed;
  5. Direct buried where identified for such use;
  6. In cable tray;
  7. In any raceway;
  8. As open runs of cable;
  9. As aerial cable on a messenger;
  10. In hazardous (classified) locations as permitted in Articles 501, 502, 503, and 504;
  11. In dry locations and embedded in plaster finish on brick or other masonry except in damp or wet locations;
  12. In wet locations where any of the following conditions are met:
    1. The metallic covering is impervious to moisture.
    2. A lead sheath or moisture-impervious jacket is provided under the metal covering.
    3. The insulated conductors under the metallic covering are listed for use in wet locations.

Exception: See Section 501-4(b), Exception.

(FPN): See Section 300-6 for protection against corrosion.

•334-4. Uses Not Permitted. Type MC cable shall not be used where exposed to destructive corrosive conditions, such as direct burial in the earth, in concrete, or where exposed to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids.

Exception: Where the metallic sheath is suitable for the conditions or is protected by material suitable for the conditions.

B. Installation

•334-10. Installation. Type MC cable shall be installed in compliance with Articles 300, 710, 725, and Section 770-52 as applicable.

(a) Support. Type MC cable shall be supported and secured at intervals not exceeding 6 ft (1.83 m). Cables containing four or fewer conductors, sized no larger than No. 10, shall be secured within 12 in. (305 mm) of every box, cabinet, or fitting.

Exception No. 1: Lengths not more than 6 ft (1.83 m) from an outlet for connections within an accessible ceiling to lighting fixtures or equipment.

Exception No. 2: Where Type MC cable is fished.

Exception No. 3: Cables installed in other than vertical runs through bored or punched holes in wood or metal framing members, or through notches in wooden framing members and protected by a steel plate at least 1/16-in. (1.59-mm) thick, shall be considered supported and secured where such support does not exceed 6 ft (1.83 m) intervals. Cables containing four or fewer conductors sized no larger than No. 10 shall be secured within 12 in. (305 mm) of each box, cabinet, fitting, or other cable termination.

(b) Cable Tray. Type MC cable installed in cable tray shall comply with Article 318.

(c) Direct Buried. Direct buried cable shall comply with Section 300-5 or 710-4, as appropriate.

(d) Installed as Service-Entrance Cable. Type MC cable installed as service-entrance cable shall comply with Article 230.

(e) Installed Outside of Buildings or as Aerial Cable. Type MC cable installed outside of buildings or as aerial cable shall comply with Article 225 and Article 321.

(f) Through or Parallel to Joists, Studs, and Rafters. Type MC cable shall comply with Section 300-4 where installed through or parallel to joists, studs, rafters, or similar wood or metal members.

(g) In Accessible Attics. The installation of Type MC cable in accessible attics or roof spaces shall also comply with Section 333-12.

•334-11. Bending Radius. All bends shall be so made that the cable will not be damaged, and the radius of the curve of the inner edge of any bend shall not be less than shown below.

(a) Smooth Sheath.

  1. Ten times the external diameter of the metallic sheath for cable not more than 3/4 in. (19 mm) in external dia 2meter;
  2. Twelve times the external diameter of the metallic sheath for cable more than 3/4 in. (19 mm) but not more than 1 1/2 in. (38 mm) in external diameter;
  3. Fifteen times the external diameter of the metallic sheath for cable more than 1 1/2 in. (38 mm) in external diameter.

(b) Interlocked-type Armor or Corrugated Sheath. Seven times the external diameter of the metallic sheath.

(c) Shielded Conductors. Twelve times the overall diameter of one of the individual conductors or seven times the overall diameter of the multiconductor cable, whichever is greater.

•334-12. Fittings. Fittings used for connecting Type MC cable to boxes, cabinets, or other equipment shall be listed and identified for such use. Where single-conductor cables enter ferrous metal boxes or cabinets, the installation shall comply with Section 300-20 to prevent inductive heating.

•334-13. Ampacity. The ampacity of Type MC cable shall be in accordance with Section 310-15.

Exception No. 1: The ampacities for Type MC cable installed in cable tray shall be determined in accordance with Sections 318-11 and 318-13.

Exception No. 2: The ampacities of No. 18 and No. 16 conductors shall be in accordance with Table 402-5.

(FPN): See Section 310-10 for temperature limitation of conductors.

C. Construction Specifications

•334-20. Conductors. The conductors shall be of copper, aluminum, or copper-clad aluminum, solid or stranded. The minimum conductor size shall be No. 18 copper and No. 12 aluminum or copper-clad aluminum.

•334-21. Insulation. The insulated conductors shall comply with (a) or (b) below.

(a) 600 Volts. Insulated conductors in sizes No. 18 and 16 shall be of a type listed in Table 402-3, with a maximum operating temperature not less than 90°C (194°F), and as permitted by Section 725-27. Conductors larger than No. 16 shall be of a type listed in Table 310-13 or of a type identified for use in MC cable.

(b) Over 600 Volts. Insulated conductors shall be of a type listed in Tables 310-61 through 310-64.

•334-22. Metallic Sheath. The metallic covering shall be one of the following types: smooth metallic sheath, welded and corrugated metallic sheath, interlocking metal tape armor. The metallic sheath shall be continuous and close fitting. Supplemental protection of an outer covering of corrosion-resistant material shall be permitted and shall be required where such protection is needed. The sheath shall not be used as a current-carrying conductor.

(FPN): See Section 300-6 for protection against corrosion.

•334-23. Grounding. Type MC cable shall provide an adequate path for equipment grounding as required by Article 250.

•334-24. Marking. The provisions of Section 310-11 shall apply. Cables that are flame-retardant and have limited-smoke characteristics shall be permitted to be identified with the suffix LS.

 

 

  
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