Fire safety is a major concern when working on any wire or cable job. Precautions should be taken to ensure that the wire or cable you choose meets all fire prevention requirements deemed necessary for your application, whether it be riser, plenum, or otherwise.
Standards organizations such as Underwriters Laboratories (UL) and CSA International work hard to develop testing and standards that promote quality and safety consciousness in all products, including wire and cable. These standards play an important role in the wire and cable industry for both the manufacturer and the end-user.
Generally, flame tests concern the amount of smoke and flame produced when a cable is exposed to fire. They also help to determine flame retardancy, or the cable’s ability to stop burning once a heat source is removed. These tests are set up under specific conditions that replicate actual wire and cable applications. Here is a rundown of some of the major flame tests you could see referenced on a cable spec sheet:
UL VW-1 Vertical Wire Flame Test
This simple test was the first developed to study flame propagation on wire and cable. It was designed to identify and reject flammable wires.
The VW-1 test begins with a 24 in. wire or cable sample held vertically by two clamps. A Tirrell burner is then mounted at a 20° angle so that the inner flame makes contact with the wire’s surface. Below the burner is surgical cotton and above the burner, near the top of the sample, is a paper indicator flag.
During the test, the flame is applied for a series of 5 distinct 15-second intervals. For each of these 5 intervals, the flame is only reapplied after 15 seconds or after the sample stops burning.
To pass, the cable must not burn longer than one minute, and the surgical cotton and the paper indicator flag cannot ignite. This test is performed on individual wires such as RHH/RHW and XHHW-2 wires. However, cables such as CL3X and CL2X must also pass the VW-1 test.
UL 910 Plenum Test
Cables must pass this test in order to be considered plenum-rated by Underwriters Laboratories. A plenum space is any space used to circulate air through a building; this could mean ducts or the area behind dropped ceilings or raised floors.
In this test, a 25 ft. Stein tunnel test furnace holds a 1 ft. wide cable rack filled with 24 ft. lengths of cable, lined up in a single layer. The cables are then ignited using an 88 kW methane flame while a 240 ft. /min. draft helps to spread the flame. The test goes on for 20 minutes while the flame spread is observed through windows spaced 1ft apart. Smoke is measured by a photocell located in the exhaust duct.
To pass this test, the flame must not spread more than 5 ft. beyond the end of the 4 1/2 ft. ignition flame. Smoke density must have a maximum optical density of 0.5 and a 0.15 maximum average optical density.
UL 1581 Vertical Tray Flame Test
This is a general-purpose vertical tray flame test. Cables are attached to a 1 ft. wide, 8 ft. metal ladder vertical cable tray. 24 inches beneath the cable, a 10-inch ribbon burner with an air/propane mixture applies a 70,000 BTU/hr flame for 20 minutes.
The cable must self-extinguish before reaching the top of the tray in order to pass this tray cable test.
This is very similar to the UL 1581 test, but with the addition of smoke emission requirements. Cables must pass this test to be listed as “limited smoke.” Type TC tray cables, Type PLTC power limited tray cables, Type ITC cables, Type CM cables, Type CL2 cables, and Type CL3 cables are all popular products that must pass the UL 1685 flame test.
UL 1666 Vertical Chamber Test
This test is designed to test the flame retardancy of riser cables. The UL test takes place in a 12 ft. high simulated shaft, with a cable running through it and a 145 kW propane burner at the bottom. The burner applies flame for 30 minutes. Flames may not extend past the 12 ft. mark for the cable to pass this test.
CSA Flame Tests
FT1-Vertical Flame Test
This is the Canadian equivalent of UL’s VW-1 Test. The cable sample is exposed to 5 separate 15-second intervals of 500-watt flame application.
For a cable to pass this test, it must stop burning in under a minute once the final flame is removed and the indicator flag must not burn more than 25%.
FT2-Horizontal Flame Test
In this test, a 500-watt flame is applied to a horizontal wire or cable sample for 30 seconds. To pass, the cable must extinguish itself once the flame is removed and the cotton batting beneath the cable must not ignite.
FT4-Vertical Tray Flame Test
For this test, a cable sample is placed in a vertical tray where a 70,000 BTU/hr flame is applied for 20 minutes. A cable passes the FT4 test if it does not char more than 59 inches from the flame application point.
FT6-Horizontal Flame and Smoke Test
The FT6 Horizontal Flame and Smoke Test are the same as the UL 910 Flame Test. To pass, the flame spread must not exceed 4.92 ft. For smoke, the peak optical density may not exceed 0.5 and the maximum average optical density may not exceed 0.15.
MSHA Flame Tests
MSHA Flame Test (US Code of Federal Regulations 30 CFR Part 7.407)
MSHA stands for “Mine Safety and Health Administration.” The MSHA requires this test to determine the fire resistance of cables used in the mining industry.
In this test, 3 feet of cable is mounted horizontally and connected to a source of current. The current raises the conductors’ temperature to 204°C. Meanwhile, a flame is applied to the center of the cable for one minute.
This test must be performed on three different cable samples. For cables to pass, they must not burn for longer than 4 minutes and no more than 6 inches of the cable may be burned or charred.
So what do these flame tests mean to you, the consumer? Most importantly, they give you peace of mind and a sense of security when it comes to your product choices. The tests developed by reputable standards organizations provide you with safety information, as well as information on the quality of the product you purchase.
Many of them also give you the information necessary to meet the requirements of the National Electrical Code. Being aware of these standards and the newest cable flame tests means you can make informed decisions about the wire and cable you purchase for your next project.