Relevant Standards:
Limited combustible (LC) cable can be used in all types of buildings. The term describes both electrical and optical fiber cable that meets requirements for cable in ceiling and raised floor plenums in accordance with NFPA 90A, Standard for the Installation of Air Conditioning and Ventilating Systems.
LC cable also meets the requirements of the National Electrical Code (NEC) for cable used in ducts, plenums and other spaces used for environmental air in accordance with Articles 725, 760, 770, 800, 820 and 830.
Requirements for cable installation span across Michigan's Building, Electrical, Mechanical and Fire Codes. In addition, Michigan's state fire safety inspectors utilize NFPA 101 (different yearly versions, depending on the occupancy classification of the structure). Therefore, LC cable does meet the requirements of the various codes, but these requirements are not directly related and so must all be clearly understood.
1. NFPA 90A, Standard for the Installation of Air Conditioning and Ventilating Systems (2002)
- Specifies combustibility requirements, such as flame spread, smoke and fuel load requirements for materials permitted in plenum spaces and exposed to air flow
- Requires that all materials exposed to the airflow within a plenum must be rated noncombustible or limited combustible
- Materials allowed in the plenum must have a Smoke Developed rating of 50 or less
- Lesser combustible exception cable is also allowed, but see NFPA 13 for potential added protection requirements in sprinklered buildings
2. National Electric Code (NEC)
- Governs the installation of materials allowed by NFPA 90A in plenum spaces
- 2002 NEC requires that abandoned, unused or unmarked cable, or cable not tagged for future use be removed
- NEC 2005 now refers users to NFPA 13 (2002) for additional fire protection requirements when allowing traditional exposed combustible exception plenum cables
3. NFPA 13,
Installation of Sprinkler Systems
- NFPA 13 (1999 and 2002) requires that plenum sprinklers be installed in sprinklered buildings if there is a loading of unprotected combustible materials such as traditional CMP, OFNP, CATVP plenum cables
- In other words, when a building is sprinklered, sprinklers are also required in concealed spaces, such as plenums, when unprotected combustible materials are present
- Sprinklers are not required if the combustible exception cables are put in metal conduit, or if the cables are listed and marked Limited Combustible FHC 25/50
- Section 8.14.1 lists the requirements concerning sprinklers in concealed spaces containing exposed combustibles
- All concealed spaces enclosed wholly or partly by exposed combustible construction shall be protected by sprinklers except in concealed spaces where sprinklers are not required to be installed by 8.14.1.2.1 through 8.14.1.2.15.
- Section 8.14.1.2, Concealed Spaces not Requiring Sprinkler Protection, says that noncombustible and limited combustible concealed spaces with no combustible loading having no access shall not require sprinkler protection
4. Underwriters Laboratories (UL) has developed a listing category for LC cable.
- Limited Combustible Cable (OWKZ) covers electrical and optical fiber cable that meets the primary non-combustible or limited combustible, and smoke developed requirements for materials as specified and defined in NFPA 90A
- UL listing procedures for LC cable can be found in Subject 2424, Outline of Investigation for Cable Marked 'Limited Combustible'
