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Are we a hair's breadth from disaster?

PRIOR TO MARCH 1989, fire cables were required to be the heaviest duty cables of all power-limited or low-voltage cables. These cables were designed for life-safety fire alarm systems to protect lives in homes, businesses, schools, hotels, retail stores, and airports. In 1965, 7,300 people were killed in the United States by fire and smoke; in 1986, this number had dropped to 4,800, due in part to the stricter standards.

Cables are used to transmit a signal or power a device. In their basic form, cables have inner conductors-commonly made of copper wire-that are insulated with a nonconductive material, then twisted together with a jacket covering all the materials. The cable must be fire resistant to be UL listed, as required by the 1987 National Electrical Code (NEC). The insulation material surrounds the conductors to provide electrical insulation, to improve signal quality and speed, and to protect against electrical shorts.

While requirements for most safety equipment are becoming more stringent, Underwriters Laboratories has reduced requirements for fire alarm cables under its UL 1424, dated February 29, 1989. These changes - which have not been tested-could affect the electrical properties, physical strength, and operating life of cables used for life safety systems.

Prior to UL 1424, the minimum allowable insulation thickness was 10 mil (.010 in.). Following UL 1424, minimum allowable insulation thickness is 5 mil (.005 in.). From 10 mil to 5 mil is a 50 percent reduction in insulation which may affect the electrical performance of the cable. The signal may not be transmitted as clearly or as far. Will the signal be reliable?

Fire cables are used for more than just signaling and voice communications. Some of the cables activate alarm bells, horns, and buzzers that require power to operate. If a cable fails due to excess power with too little insulation, the alarm warning system will not sound the alarm. An average of one fault per 3,000 ft. of single insulated conductor in a cable is allowed, meaning UL-listed cables could be shipped from wire manufacturers with holes and breaks in the insulation of the individual conductors.

Over time, moisture may penetrate the fire cable, leading to an electrical short, making the cable inoperable. The overall jacket protects the conductors from physical abuse, crushing, heat, moisture, cuts, and scrapes during installation. When installed, these cables are pulled through metal conduits, trays, drilled holes, open areas between floors, walls, and over sharp objects.

Prior to February 29, 1989, minimum acceptable jacket thicknesses were 30 mil (.030 in.) or more for all fire cables. The minimum acceptable thickness allowed at any point on the jacket now is 6 mil (.006 in.)-a reduction of 24 mil or 80 percent in jacket thickness. A human hair is about 2 mil thick. New fire cables could have jackets three hairs thick, about the thickness of a two-ply paper towel. Will these cables stand up to the abuse of installation?

Jacket and insulation materials are listed with a temperature rating that reflects how long a material will retain its elasticity at certain temperatures. The higher the temperature rating, the longer it lasts. Fire cables used to be rated at 105[deg]Corgreater-now there is no temperature requirement. Many materials listed at 60' C can now be used for fire cables and be installed over heat ducts, near lighting fixtures, or in hot attic areas where the increased temperatures could cause the cables to break down and short out. Will these fire alarm cables last as long as the expected life of a building?

To further complicate the issue, last fall the 1990 NEC was published. Based on a long-term effort by a major long-distance telephone company, the NEC will allow communication or telephone cables to be substituted for fire alarm cables. Communication cables are used for signaling applications-their small-gauge conductors and thin insulation are not intended for powering alarm bells, horns, or buzzers. Will these cables perform on fire systems? Have they been tested for fire systems?

With life safety systems, liability is always a concern. Where does responsibility lie for false alarms or fire alarm system failures and resulting loss of life? Is the responsibility with the fire alarm manufacturer, cable manufacturer, distributor, dealer, installer, electrical and fire inspector, Underwriters Laboratories, or National Fire Protection Association? With life safety involved, can anyone afford the risk of these changes?

About the Author . . . Gary A. Ward is the product manager of electric wire and cable for Dekoron Division of Fluorocarbon in Aurora, OH, and a member of the Security Industry Association's wire standards committee.
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Title Annotation:fire cable jacket thicknesses
Author:Ward, Gary A.
Publication:Security Management
Article Type:column
Date:Mar 1, 1990
Words:763
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