Fire Cable Ratings and Fire Protection: A Comprehensive ...

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1. IEC standard for fireproof cables

In order to evaluate the flame retardant performance of cables, the International Electrotechnical Commission has formulated three IEC standards: IEC-1, IEC-2 and IEC-3. IEC-1 and IEC-2 are used to evaluate the flame retardant performance of a single cable when it is laid at an angle and vertically (corresponding to GB.3 and GB.4 standards in China). IEC-3 (corresponding to GB.5-90 in China) is used to evaluate the flame retardant performance of bundled cables when they are burned vertically. In comparison, the flame retardant performance requirements for bundled cables when they are burned vertically are much higher.

(1) IEC-1/BS-1 flame retardant grade (Flame Test On Single Vertical Insulated Wires/Cables)

This is the flame retardant standard for single cables. The test stipulates that a 60cm long sample is fixed vertically in a metal box with an opening on the front wall. A propane burner with a flame length of 175mm contacts the cable at a 45-degree angle from a position 450mm from the upper fixed end of the sample. If the damaged part of the sample is no more than 50mm away from the lower part of the fixed end, the test is passed.

(2) IEC-3/BS-3 Flame retardant grade (Flame Test on Bunched Wires/Cables)

This is the flame retardant standard for bundled cables. The test stipulates that a 3.5m long cable sample is fixed on a trapezoidal test frame with iron wire. The number of samples is determined by the non-metallic materials required for different classifications. The sample is hung vertically on the back wall of the combustion furnace, and air is introduced into the combustion furnace through the air inlet on the bottom plate. The propane flat burner contacts the sample with a flame of 750°C. Under forced air blowing (airflow discharge 5m3/min, wind speed 0.9m/sec), the sample must not burn within 20 minutes of vertical burning, and the cable must extinguish itself within 2.5 meters of flame spread. IEC is divided into Class A, Class B, Class C and Class D to evaluate the flame retardant performance.

2. UL standard for fireproof cables

Any cable listed by UL that has been tested and verified to meet a certain fireproof level can be printed with the UL identification word, fireproof level and approval number on the cable.

(1) Pressurized Grade - CMP Grade (Plenum Flame Test/Steiner Tunnel Test)

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This is the cable with the highest requirements in the UL fire protection standard (Plenum Cable). The applicable safety standard is UL910 (UL Standard for Safety Test for Flame-Propagation and Smoke-Density Values for Electrical and Optical-Fiber Cables Used in Spaces Transporting Environmental Air). The test stipulates that multiple samples are laid on the horizontal air duct of the device and burned for 20 minutes with an 87.9KW gas Bunsen burner (300,000 BTU/Hr). The qualified standard is that the flame cannot extend beyond 5 feet from the front of the gas Bunsen burner flame. The maximum peak value of the optical density is 0.5, and the maximum average density value is 0.15. This CMP cable is usually installed in the air return pressurization system used in ventilation ducts or air handling equipment, and is recognized and adopted by Canada and the United States. FEP/PLENUM materials that meet the UL910 standard have better flame retardancy than low-smoke halogen-free materials that meet the IEC-1 and IEC-3 standards, and the smoke density is low when burning.

(2) Trunk-CMR grade (Riser Flame Test)

This is a commercial-grade cable (Riser Cable) in the UL standard. The applicable safety standard is UL (Test for flame propagation height of electrical and optical-fiber cables installed vertically in shafts. Flame propagation test standard for high-voltage cables and optical-fiber cables installed vertically in shafts). The experiment stipulates that multiple specimens are laid on a simulated vertical shaft and a specified 154.5KW gas Bunsen burner (527, 500BTU/Hr) is used for 30 minutes. The qualified standard is that the flame cannot spread to the upper part of a room 12 feet high. Trunk-grade cables have no smoke density specifications and are generally used for vertical and horizontal wiring on floors.

(3) Commercial Grade - CM Grade (Vertial Tray Flame Test)

This is the General Purpose Cable in the UL standard, and the applicable safety standard is UL (REFERENCE STANDRD FOR ELECTRICAL WIRES CABLES AND FLEXIBLE CORDS UL-). The experiment stipulates that multiple samples are laid on a vertical 8-foot-high bracket and burned with a specified 20KW ribbon blowtorch (70,000 BTU/Hr) for 20 minutes. The qualified standard is that the flame cannot spread to the upper end of the cable and extinguish itself. UL is similar to IEC-3C, except that the number of cables laid is different. Commercial grade cables have no smoke concentration specifications and are generally only used for horizontal wiring on the same floor, not for vertical wiring on the floor.

(4) General Purpose Cable - CMG (Vertical Tray Flame Test)

This is a general purpose cable in the UL standard, and the applicable safety standard is UL. The test conditions of commercial and general purpose cables are similar, and both are approved for use in Canada and the United States. General purpose cables do not have smoke concentration specifications and are generally only used for horizontal wiring on the same floor, not for vertical wiring on the floor.

(5) Home Grade - CMX (Vertical Wire Flame Test)

This is a restricted cable in the UL standard, and the applicable safety standard is UL, VW-1. The test stipulates that the sample is kept vertical, burned with a test blowtorch (30,000 TU/Hr) for 15 seconds, then stopped for 15 seconds, and repeated 5 times. The pass standard is that the residual flame cannot exceed 60 seconds, the sample cannot be burned by more than 25%, and the surgical cotton pad at the bottom cannot be ignited by falling objects. UL-VW-1 is similar to IEC-1, but with a different burning time. This rating also has no smoke or toxicity specifications and is only used in home or small office systems where a single cable is laid. This type of cable should not be laid in bundles and must be sleeved. Smoke density, halogen content and toxicity rating.

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