Flame-Retardant Cable vs. Fire-Rated/Resistive Cable
What Are Flame-Retardant Cables?
The definition of flame-retardant cable is a cable that will not convey or propagate a flame as defined by the flame-retardant or propagation tests.
Flame-retardant tests measure flame propagation for both horizontal and vertical applications. There are also plenum cable flame tests for use in ducts, plenums or other spaces used for environmental air distribution. The NFPA 262 is the same as CSA FT-6; it measures flame spread and smoke generation in a simulated air handling plenum. Cables used in plenums are required to have a more stringent test than that of the horizontal or vertical flame tests.
What Are Fire-Resistive or Fire-Rated Cables?
The definition of a fire-resistive or fire-rated cable is a cable that will continue to operate in the presence of a fire. This is commonly known as a circuit integrity (CI) cable and is 2-hour fire-rated.
Mineral Insulated (MI) cable has provided this added protection for decades. MI cable construction uses copper conductors, magnesium oxide and a copper sheath. MI cable comes in single and multiconductor versions. This 2-hour fire-resistive cable is designed for emergency power circuits for fire pumps and emergency generators. MI is labor-intensive and difficult to install and, therefore, is rarely used in low-voltage fire protection and emergency voice systems.
With new developments in wire and cable technology and recent changes in the NEC, a variety of new products have become available. These new CI cables are commonly used in fire alarm and voice communications systems. NEC 760.176 (F) requires CI cables for NFPA fire alarm systems used to meet the survivability of critical circuits requirements and be listed for that function per NFPA 72. Conformance to the code requirements of circuit survivability will ensure the performance of the fire alarm system during a fire emergency.
CI cable also provides flexibility in planning cable routing while minimizing wall and shaft construction. CI cable is typically soft ceramifiable silicone rubber insulation with solid copper conductors. Ceramifiable silicone rubber insulation is soft and flexible until subjected to high temperatures. These CI cable constructions are as flexible as standard fire alarm cables, making them as easy to install as cables that are not fire-rated. They can be installed in standard raceways and conduit and require no special tools or hardware. Special training to handle or install is also not needed as is with MI cable.
The Main Difference
There are enormous differences between flame-retardant cables and fire-resistive cables. Typically, flame-retardant cables resist the spread of fire into a new area, whereas fire-resistive cables maintain circuit integrity and continue to work for a specific time under defined conditions. These circuit integrity cables continue to operate in the presence of a fire and are sometimes called 1-hour or 2-hour fire-rated cables. The differences between these two ratings are essential for the critical circuits required for life safety requirements.
Frequently Asked Questions
Is a flame-retardant cable also fire-rated?
No. A flame-retardant cable is not a fire-rated cable. A flame-retardant cable is designed only to restrict the spread of a fire by inhibiting combustion. Fire-resistive cables maintain circuit integrity and continue to work for a specific time under defined conditions such as fire.
When do you need a fire-rated circuit integrity cable?
Circuit integrity cable is needed when circuit integrity is essential for life safety or when it is critical to prevent a plant shut down. The NEC provides additional requirements.
What is a plenum?
A plenum is the air return path of a central air handling system. It can be either ductwork or open space over a supended celing or raised floor.
What is the difference between riser-rated and plenum-rated cables?
Plenum-rated cables have a higher flame-resistance requirement than riser-rated cables. Riser-rated cables are installed between floors through cable risers and in elevator shafts. They must self-extinguish and prevent fire from traveling up the riser between the floors or elevator shafts. A typical jacket material for riser-rated cable is PVC. Typical jacket coumpounds for plemum-rated cable are FR-PVC, FEP, PVDF and ECTFE.
Do tray cables in the U.S. need to pass a flame test?
Yes. They must pass one of the UL 1685 vertical tray flame tests to be UL-listed.