Fire-resistant cables currently in widespread use fall primarily into two categories: UL-series flame-retardant cables and low-smoke halogen-free cables. Among imported products, the majority originate from the Americas and Europe. Since fire-resistant cable standards in the Americas and Europe are incompatible with each other and reflect significantly different approaches to fire protection, both the client and the design institute find themselves in a passive position when selecting products. Each side has its own valid arguments, and ultimately, the choice often hinges on the actual financial situation.

　　What is an introduction to fire-resistant cables? Let’s take a look together below. Currently, the two main types of fire-resistant cables widely used are UL-series flame-retardant cables and low-smoke halogen-free cables. Among imported products, most originate from the Americas and Europe. Since the fire-resistance standards in the Americas and Europe are incompatible with each other and their approaches to fire protection differ significantly, both the client and the design institute often find themselves in a passive position when selecting products—each side has its own valid reasons. Ultimately, the choice usually depends on the actual financial situation. What are the different types of fire-resistant cables? Let’s explore this together below. The UL flame-retardant standards mainly include several grades: CM, CMG, and CMX. 1) The highest-grade—CMP grade (Plenum Flame Test/Steiner Tunnel Test): This is the cable with the strictest fire-resistance requirements under the UL standard (Plenum Cable), and it complies with the UL910 safety standard. The test involves placing multiple samples on horizontal air ducts within an installation and exposing them to a gas Bunsen burner with a power output of 87.9 kilowatts (300,000 BTU/hr) for 20 minutes. The passing criterion is that the flame must not extend beyond 5 feet in front of the Bunsen burner’s flame. The peak value of light density shall not exceed 0.5, and the average light density value shall not exceed 0.15.

　　This CMP cable is typically installed in air-return pressurization systems used in ventilation ducts or air-handling equipment and is recognized in both Canada and the United States. FEP/FLENUM materials that comply with UL910 standards exhibit superior flame-retardant performance and lower smoke concentrations during combustion compared to low-smoke, halogen-free materials that meet IEC60332-1 and IEC60332-3 standards. 2) Riser Cable—CMR Grade (Vertical Flame Test—Riser Cable Test): This is a UL-standard enterprise-grade cable (Riser Cable), with safety certification under UL1666. The test procedure involves installing multiple samples on a simulated vertical axis and exposing them for 30 minutes to a specified gas Bunsen burner delivering 154.5 kilowatts (527,500 BTU/hr). The pass criterion is that the flame must not propagate beyond the top of a 12-foot-high room. Riser cables do not have specific smoke-density regulations and are typically used for vertical and horizontal wiring within a single floor. 3) Commercial Cable—CM Grade (Vertical Flame Test—Vertical Tray Flame Test): This is a commercial cable conforming to UL standards, with safety certification under UL1581. The test procedure requires placing multiple samples on an 8-foot-high vertical base and subjecting them to a prescribed 20-kilowatt ribbon-type burner (70,000 BTU/hr) for 20 minutes. The pass criterion is that the flame must not spread beyond the top of the cable and must self-extinguish. UL1581 is similar to IEC60332-3C, but differs in the number of cable cores wrapped around the central core. Commercial cables do not have specific smoke-density regulations and are generally suitable only for horizontal wiring within the same floor; they are not intended for vertical cabling between floors.

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