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What is a UL Two Hour Fire Rating?

When it comes to fire rated wiring, there is a lot of discussion around safety standards and codes that building professionals need to follow. 

Let’s discover who is behind these codes, and why they’re an important consideration when designing or retrofitting a building.  

What Does UL Mean? 

UL LLC is a safety certification company established in 1894. It is widely known as Underwriters Laboratory, hence the UL name. The company has worked for over one hundred years to analyze the safety of evolving technologies, and is one of the top companies approved to safety test in North America by OSHA.  

Other than Electrical Code, UL maintains standards for:  

  • Sustainability  
  • Life Safety  
  • Building Products  
  • Plastic Materials  
  • Wire and Cable  
  • Industrial Control Equipment  

Essentially, UL performs tests on products to make sure they are meeting codes and standards.   

Is UL Certified Required? 

The National Fire Protection Association (NFPA) sets the standards for safe installation of electrical equipment in the United States. While this is not federally mandated, many states have adopted this standard.   

The National Electric Code (NEC) is also known as NFPA 70. This is developed and amended by the NFPA Committee, and is approved as an American national standard. The NEC recently required that many critical electrical circuits are protected with a minimum two hours of fire protection. This two-hour fire rating applies to:  

  • Emergency power supplies  
  • Firefighter elevators  
  • Fire pumps  
  • Smoke venting fans  
  • Fire alarms  
  • And more  

While there are other standard agencies like UL, they are one of the most recognized companies in the country. Meeting the UL test for a two-hour system often means meeting NEC requirements.  

What Does it Take to Be UL Certified? 

The UL 2196 / ULC S-139 2-hour cable testing standard consists of a specific type of fire exposure followed by a water hose stream. Cables are energized during the fire test and after the hose stream to ensure that the circuit integrity has been maintained for the duration of the test. 

Part of this test is to detect electrical failure of the tested cable. 

During the test, the cables and supports are mounted and powered at 600 V (line to line) or 347 V (ground). Then, a furnace produces the required temperature for two hours. Within five minutes of the fire testing, the power is disconnected and the area is sprayed with a fire hose at 30 PSI for a duration of 0.9 seconds per square foot. After this section of the test, power is reconnected to test whether or not the circuits re-engage and the lights turn on.  The test is completed when the lights turn on and stay lit for 5 minutes following testing.  

Mineral insulated copper-clad cables (MI cable), like nVent PYROTENAX cables, are the only ones to meet the 2-hour vertical and horizontal UL fire test with no limitations.  

Why Should You Seek UL Testing? 

While these codes and standards are not law at the federal level, many states have adopted them as necessary for new buildings and retrofits.  

In the United States, companies and even cities can face liability for creating a situation that results in loss of life or property. This motivates states to adopt these codes and standards for buildings, so that damages and subsequent lawsuits can be avoided.  

Due to the need to adopt a single set of code laws, the NEC has become widely known as the industry standard.  

Understanding building and electrical code can be a challenge, especially when they change as new technology and research emerges.  

If you’re interested in learning more about the individual codes that govern critical circuits, visit our YouTube channel and watch our code education video series, or read more about them on the nVent PYROTENAX blog.