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When Does 2” Not Equal 2 Hours?

Many buildings use concrete construction methods as a way to protect wiring to critical circuits. This process of encasing standard building wires supplying power to critical life-saving equipment with up to two inches of concrete is very common.  

While this approach has historically been accepted, a technical note released by the NFPA shows an evolution in building codes and standards may be long past due.  

Let’s explore the fire resistance of concrete, and how it compares to fire-rated wiring solutions.

BTW, The Answer is: 2” of concrete only provides 1 hour of fire protection – Let’s go deeper.  


Why is Concrete an Option for Buildings? 

Concrete as a structure and a material is inherently fire resistant. It’s a non-combustible material with a slow rate of heat transfer, making it a natural choice for building fire protection.

In fact, it was approved for one hour of fire protection by the NFPA. All critical wires and circuitry could be encased in the concrete for a relatively low cost.  

If the question is – is concrete fire resistant? The simple answer is yes, but this does not mean it’s the most optimal material for modern building fire protection.  


The Evolution of Building Codes  

As buildings have grown larger and the time required to safely evacuate and respond to fire has grown, a number of NEC building standards have upgraded from one hour of fire protection to two hours over the last twenty years. These include:   

  • Article 695 “Fire Pumps” requires 2 hour protection per 2008 NEC 
  • Article 700 “Emergency Systems” requires 2 hour of Protection per 2011 NEC 
  • Article 708 “Critical Operating Power Systems requires 2 hour Protection per 2011 NEC 
  • New Article 728 “Fire-Resistive Cable Systems” in 2014 
  • Article 760 “Fire Alarm Systems” requires 
  • 2 hour Protection per 2005 NEC 
  • NFPA 72 “Fire Alarms” requires 2 hour “Survivable Circuit” and cables must be installed per Article 760

These updates fell in line with NFPA codes requiring two hours of fire protection applied to emergency power supply generators, elevator circuits, fire pump circuits, smoke venting fans and more.  

As of 2022 more than 42 states mandated a minimum two-hour fire rating. This means critical circuits should remain operational in temperatures from 1000°F (537°C) at 5 minutes to 1850°F (1010°C) at 120 minutes.  


How Do Concrete Methods and MI Cable Compare for Fire Protection? 

The main problem with concrete and fire protection, is that you need more inches of thickness for more hours of protection. To meet the current codes and standards, most concrete encasements would need to be between three and five inches thick, depending on the aggregate used. This means that buildings with one or two inches of concrete are not currently meeting the spirit of NFPA or NEC code and are not supplying two hours of fire protection.   


Downside of Using Concrete for Fire Protection in Buildings:  

  • Buildings with one or two inches of concrete are not currently meeting 2 hours of fire protection 
  • Using more concrete would lead to less usable space, a critical aspect for modern building design 
  • Lack of approval or testing once installed can lead to inadequate protection  
  • Concrete is prone to  damage  which reduces protection
  • Concrete is not ideal for building retrofits or remodels


Upside of using PYROTENAX SYSTEM 1850 MI cable for Fire Protection in Buildings:  

  • PYROTENAX MI cable is UL/ULC fire rated for two hours of protection 
  • PYROTENAX MI cable is Free air rated so you can deliver more amps while consuming less usable space 
  • PYROTENAX MI cable can be installed in tight, or hard to maneuver spaces  
  • PYROTENAX MI cable can withstand the impact of a blow, or falling concrete, etc.
  • PYROTENAX MI cable can be spliced and rerouted as buildings evolve over time


For well over one hundred years, fire safety codes have saved lives and property by promoting best practices in building design. With the availability of fire-rated products, building professionals are better equipped to specify the safest systems.  

To learn more, please visit us at Fire Rated Wiring | System Advantages | nVent PYROTENAX
To download our specifications please visit Manufacturer