Article 332

ARTICLE 332

Mineral-Insulated, Metal-Sheathed Cable: Type MI

Part I. General

1. Scope. This article covers the use, installation, and construction specifications for mineral-insulated, metal- sheathed cable, Type MI.
2. Definition.

Mineral-Insulated, Metal-Sheathed Cable, Type MI. A factory assembly of one or more conductors insulated with a highly

332.6 ARTICLE 332 — MINERAL-INSULATED, METAL-SHEATHED CABLE: TYPE MI

compressed refractory mineral insulation and enclosed in a liquidtight and gastight continuous copper or alloy steel sheath.

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332.6 Listing Requirements. Type MI cable and associated fittings shall be listed.

Part II. Installation

332.10 Uses Permitted. Type MI cable shall be permitted as follows:

1. For services, feeders, and branch circuits
2. For power, lighting, control, and signal circuits
3. In dry, wet, or continuously moist locations
4. Indoors or outdoors
5. Where exposed or concealed
6. Where embedded in plaster, concrete, fill, or other masonry, whether above or below grade
7. In hazardous (classified) locations where specifically permitted by other articles in this Code
8. Where exposed to oil and gasoline
9. Where exposed to corrosive conditions not deteriorating to its sheath
10. In underground runs where suitably protected against physical damage and corrosive conditions
11. In or attached to cable tray

Informational Note: The “Uses Permitted” is not an all-inclusive list.

332.12 Uses Not Permitted. Type MI cable shall not be used under the following conditions or in the following locations:

1. In underground runs unless protected from physical damage, where necessary
2. Where exposed to conditions that are destructive and corrosive to the metallic sheath, unless additional protec‐ tion is provided

332.17 Through or Parallel to Framing Members. Type MI cable shall be protected in accordance with 300.4 where instal‐ led through or parallel to framing members.

332.24 Bending Radius. Bends in Type MI cable shall be so made that the cable will not be damaged. The radius of the inner edge of any bend shall not be less than required as follows:

1. Five times the external diameter of the metallic sheath for cable not more than 19 mm (3∕4 in.) in external diame‐ ter
2. Ten times the external diameter of the metallic sheath for cable greater than 19 mm (3∕4 in.) but not more than 25 mm (1 in.) in external diameter

1. Securing and Supporting. Type MI cable shall be supported and secured by staples, straps, hangers, or similar fittings, designed and installed so as not to damage the cable, at intervals not exceeding 1.8 m (6 ft).
   1. Horizontal Runs Through Holes and Notches. In other than vertical runs, cables installed in accordance with 300.4 shall be considered supported and secured where such support does not exceed 1.8 m (6 ft) intervals.
   2. Unsupported Cable. Type MI cable shall be permitted to be unsupported where the cable is fished between access pointsthrough concealed spaces in finished buildings or structures and supporting is impracticable.
   3. Cable Trays. All MI cable installed in cable trays shall comply with 392.30(A).
2. Single Conductors. Where single-conductor cables are used, all phase conductors and, where used, the neutral conductor shall be grouped together to minimize induced volt‐ age on the sheath.

332.40 Boxes and Fittings.

1. Fittings. Fittings used for connecting Type MI cable to boxes, cabinets, or other equipment shall be identified for such use.
2. Terminal Seals. Where Type MI cable terminates, an end seal fitting shall be installed immediately after stripping to prevent the entrance of moisture into the insulation. The conductors extending beyond the sheath shall be individually provided with an insulating material.

332.80 Ampacity. The ampacity of Type MI cable shall be determined in accordance with 310.15. The conductor temper‐ ature at the end seal fitting shall not exceed the temperature rating of the listed end seal fitting, and the installation shall not exceed the temperature ratings of terminations or equip‐ ment.

1. Type MI Cable Installed in Cable Tray. The ampacities for Type MI cable installed in cable tray shall be determined in accordance with 392.80(A).
2. Single Type MI Conductors Grouped Together. Where single Type MI conductors are grouped together in a triangular or square configuration, as required by 332.31, and installed on a messenger or exposed with a maintained free air space 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 of Table 310.15(B)(17).

Part III. Construction Specifications

332.104 Conductors. Type MI cable conductors shall be of solid copper, nickel, or nickel-coated copper with a resistance corresponding to standard AWG and kcmil sizes.

332.108 Equipment Grounding Conductor. Where the outer sheath is made of copper, it shall provide an adequate path to serve as an equipment grounding conductor. Where the outer sheath is made of steel, a separate equipment grounding conductor shall be provided.

332.112 Insulation. The conductor insulation in Type MI cable shall be a highly compressed refractory mineral that provides proper spacing for all conductors.

332.116 Sheath. The outer sheath shall be of a continuous construction to provide mechanical protection and moisture seal.