11 KiB
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Article 330 Metal-Clad Cable: Type MC |
Article 330 Metal-Clad Cable: Type MC
Part I. General
330.1 Scope.
This article covers the use, installation, and construction specifications of metal-clad cable, Type MC.
330.2 Definition.
The definition in this section shall apply within this article and throughout the Code.
Metal Clad Cable, Type MC.
A factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth or corrugated metallic sheath.
330.6 Listing Requirements.
Type MC cable shall be listed. Fittings used for connecting Type MC cable to boxes, cabinets, or other equipment shall be listed and identified for such use.
Part II. Installation
330.10 Uses Permitted.
330.10(A) General Uses.
Type MC cable shall be permitted as follows:
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(1) For services, feeders, and branch circuits.
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(2) For power, lighting, control, and signal circuits.
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(3) Indoors or outdoors.
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(4) Exposed or concealed.
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(5) To be direct buried where identified for such use.
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(6) In cable tray where identified for such use.
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(7) In any raceway.
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(8) As aerial cable on a messenger.
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(9) In hazardous (classified) locations where specifically permitted by other articles in this Code.
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(10) In dry locations and embedded in plaster finish on brick or other masonry except in damp or wet locations.
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(11) In wet locations where a corrosion-resistant jacket is provided over the metallic covering and any of the following conditions are met:
- a. The metallic covering is impervious to moisture.
- b. A jacket resistant to moisture is provided under the metal covering.
- c. The insulated conductors under the metallic covering are listed for use in wet locations.
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(12) Where single-conductor cables are used, all phase conductors and, where used, the grounded conductor shall be grouped together to minimize induced voltage on the sheath.
330.10(B) Specific Uses.
Type MC cable shall be permitted to be installed in compliance with Parts II and III of Article 725 and 770.133 as applicable and in accordance with 330.10(B)(1) through (B)(4).
[!info] Informational Note: The "Uses Permitted" is not an all-inclusive list.
330.10(B)(1) Cable Tray.
Type MC cable installed in cable tray shall comply with nfpa-70_392_cable-tray#392.10 Uses Permitted., nfpa-70_392_cable-tray#392.12 Uses Not Permitted., 392.18, 392.20, 392.22, 392.30, 392.46, 392.56, 392.60(C), and 392.80.
330.10(B)(2) Direct Buried.
Direct-buried cable shall comply with 300.5 or 300.50, as appropriate.
330.10(B)(3) Installed as Service-Entrance Cable.
Type MC cable installed as service-entrance cable shall be permitted in accordance with 230.43.
330.10(B)(4) Installed Outside of Buildings or Structures or as Aerial Cable.
Type MC cable installed outside of buildings or structures or as aerial cable shall comply with 225.10, 396.10, and 396.12.
330.12 Uses Not Permitted.
Type MC cable shall not be used under either of the following conditions:
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(1) Where subject to physical damage
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(2) Where exposed to any of the destructive corrosive conditions in (a) or (b), unless the metallic sheath or armor is resistant to the conditions or is protected by material resistant to the conditions:
- a. Direct buried in the earth or embedded in concrete unless identified for direct burial
- b. Exposed to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids
330.15 Exposed Work.
Exposed runs of cable, except as provided in 300.11(B), shall closely follow the surface of the building finish or of running boards.
Exposed runs shall also be permitted to be installed on the underside of joists where supported at each joist and located so as not to be subject to physical damage.
330.17 Through or Parallel to Framing Members.
Type MC cable shall be protected in accordance with nfpa-70_300_general-requirements#300.4(A) Cables and Raceways Through Wood Members., nfpa-70_300_general-requirements#300.4(C) Cables Through Spaces Behind Panels Designed to Allow Access., and nfpa-70_300_general-requirements#300.4(D) Cables and Raceways Parallel to Framing Members and Furring Strips. where installed through or parallel to framing members.
330.23 In Accessible Attics.
The installation of Type MC cable in accessible attics or roof spaces shall also comply with nfpa-70_320_armored-cable#320.23 In Accessible Attics..
330.24 Bending Radius.
Bends in Type MC cable shall be so made that the cable will not be damaged. The radius of the curve of the inner edge of any bend shall not be less than required in 330.24(A) through (C).
330.24(A) Smooth Sheath.
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(1) Ten times the external diameter of the metallic sheath for cable not more than 19 mm (3⁄4 in.) in external diameter
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(2) Twelve times the external diameter of the metallic sheath for cable more than 19 mm (3⁄4 in.) but not more than 38 mm (1 1⁄2 in.) in external diameter
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(3) Fifteen times the external diameter of the metallic sheath for cable more than 38 mm (1 1⁄2 in.) in external diameter
330.24(B) Interlocked-Type Armor or Corrugated Sheath.
Seven times the external diameter of the metallic sheath.
330.24(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.
330.30 Securing and Supporting.
330.30(A) General.
Type MC cable shall be supported and secured by staples; cable ties listed and identified for securement and support; straps, hangers, or similar fittings; or other approved means designed and installed so as not to damage the cable.
330.30(B) Securing.
Unless otherwise provided, cables shall be secured at intervals not exceeding 1.8 m (6 ft). Cables containing four or fewer conductors sized no larger than 10 AWG shall be secured within 300 mm (12 in.) of every box, cabinet, fitting, or other cable termination. In vertical installations, listed cables with ungrounded conductors 250 kcmil and larger shall be permitted to be secured at intervals not exceeding 3 m (10 ft).
330.30(C) Supporting.
Unless otherwise provided, cables shall be supported at intervals not exceeding 1.8 m (6 ft).
Horizontal runs of Type MC cable installed in wooden or metal framing members or similar supporting means shall be considered supported and secured where such support does not exceed 1.8 m (6 ft) intervals.
330.30(D) Unsupported Cables.
Type MC cable shall be permitted to be unsupported and unsecured where the cable complies with any of the following:
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(1) Is fished between access points through concealed spaces in finished buildings or structures and supporting is impractical.
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(2) Is not more than 1.8 m (6 ft) in length from the last point of cable support to the point of connection to luminaires or other electrical equipment and the cable and point of connection are within an accessible ceiling.
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(3) Is Type MC of the interlocked armor type in lengths not exceeding 900 mm (3 ft) from the last point where it is securely fastened and is used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation.
For the purpose of this section, Type MC cable fittings shall be permitted as a means of cable support.
330.31 Single Conductors.
Where single-conductor cables with a nonferrous armor or sheath are used, the installation shall comply with 300.20.
330.80 Ampacity.
The ampacity of Type MC cable shall be determined in accordance with 310.14 or 311.60 for 14 AWG and larger conductors and in accordance with Table 402.5 for 18 AWG and 16 AWG conductors. The installation shall not exceed the temperature ratings of terminations and equipment.
330.80(A) Type MC Cable Installed in Cable Tray.
The ampacities for Type MC cable installed in cable tray shall be determined in accordance with 392.80.
330.80(B) Single Type MC Conductors Grouped Together.
Where single Type MC conductors are grouped together in a triangular or square configuration and installed on a messenger or exposed with a maintained free airspace of not less than 2.15 times one conductor diameter (2.15 × O.D.) of the largest conductor contained within the configuration and adjacent conductor configurations or cables, the ampacity of the conductors shall not exceed the allowable ampacities in the following tables:
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(1) Table 310.20 for conductors rated 0 volts through 2000 volts
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(2) Table 311.60(C)(67) and Table 311.60(C)(68) for conductors rated over 2000 volts
330.80(C) Thermal Insulation.
Where more than two Type MC cables containing two or more current-carrying conductors in each cable are installed in contact with thermal insulation, caulk, or sealing foam without maintaining spacing between cables, the ampacity of each conductor shall be adjusted in accordance with Table 310.15(C)(1).
Part III. Construction Specifications
330.104 Conductors.
For ungrounded, grounded, and equipment grounding conductors, the minimum conductor sizes shall be 14 AWG copper, nickel, or nickel-coated copper and 12 AWG aluminum or copper-clad aluminum.
For control and signal conductors minimum conductor sizes shall be 18 AWG copper, nickel, or nickel-coated copper, 14 AWG copperclad aluminum, and 12 AWG aluminum.
330.108 Equipment Grounding Conductor.
Where Type MC cable is used to provide an equipment grounding conductor, it shall comply with 250.118(10) and 250.122.
330.112 Insulation.
Insulated conductors shall comply with 330.112(A) or (B).
330.112(A) 1000 Volts or Less.
Insulated conductors in sizes 18 AWG and 16 AWG 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 725.49. Conductors larger than 16 AWG shall be of a type listed in Table 310.4(A) or of a type identified for use in Type MC cable.
330.112(B) Over 1000 Volts.
Insulated conductors shall be of a type listed in Table 310.4(B) and Table 311.10(A).
330.116 Sheath.
Metallic covering shall be one of the following types: smooth metallic sheath, corrugated metallic sheath, or interlocking metal tape armor. The metallic sheath shall be continuous and close fitting. A nonmagnetic sheath or armor shall be used on single conductor Type MC. 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.
[!info] Informational Note: See 300.6 for protection against corrosion.
330.130 Hazardous (Classified) Locations.
Where required to be marked MC-HL, the cable shall be listed and shall have a gas/vapor tight continuous corrugated metallic sheath, an overall jacket of suitable polymeric material, and a separate equipment grounding conductor.