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ESTIMATING MI CABLE

The purpose of MI cable is to meet the 2-hour fire rating requirement Article 332 of the NEC. It is used for critical fire protection applications. It is available in single or multi-conductor assemblies and most are rated for 600 volts.

NEC Article 332.10 Uses Permitted, are 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

MI cable can be found in the following facilities:

  1. High-rise buildings
  2. Health care facilities
  3. Historic buildings
  4. Airports
  5. Stadiums
  6. Hotels
  7. Hazardous locations


MI cable may be used for the following applications:

  1. Fire pump feeders
  2. Emergency generator feedersR
  3. Emergency exhaust fans
  4. Emergency lighting
  5. Emergency communications systems
  6. Exit signs
  7. Firefighter’s elevators


A complete MI cable takeoff would include the following:

  1. Cable lengths by number and size of conductors
  2. Number of termination fittings by cable size and conductors
  3. Splice kits if necessary
  4. Firestopping thru fire rated walls
  5. Hangers – Unistrut trapeze racks or strapping – 6 ft spacing as per NEC, vertical or horizontal supports.
  6. If installed in cable tray, appropriate straps

Things to remember:

  1. MI cable manufacturers may require minimum quantities.
  2. Terminating MI cable requires special tools.
  3. MI Cable is extremely heavy.
  4. Most manufacturers will make custom configurations.
  5. Physical protection is required where cable comes out of a slab.
  6. If encased in concrete, the cable may need to be wrapped in a protective cover.

Remember, estimating is expensive, poor estimating is costly, but quality estimating is profitable.