Fire Rating Conductors / Conduit

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Mike01

Senior Member
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MidWest
When installed in conduit (standard building wire thhn thwn in EMT RGS) does the conduit help to provide a "fire rating" for the cables. for example would conductors installed in emt be considered 1hr rated as opposed to rigid that would provide a 2hr rating. is there a table or information on this? without using special fire rated cabling or encased in concrete?
 

sparkie001

Senior Member
Metallic conduit readily conducts the heat and melts normal wire insulation. Use your favorite search engine and search for ceramified silicone insulated wire which can be installed in EMT and achieve a 2hr rating.
 
No fire rating for regular building wire in conduit.
There is wire in EMT that will get you a fire rating, such as http://www.drakausa.com/productDetail.aspx?productID=732


One item to remember with this type of rated conductor is the cost. There is a dramatic difference in the cost of the above conductor, make sure to price it properly, otherwise you will wish you never took the job.

Read the installation instructions as well, not all phases of this installation are as straight forward as Type THHN installations.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The concrete would protect the building from the wires in the conduit, but it will not protect the wires from the fire in the building. Two inches of concrete does not provide much thermal insulation from the heat of a building fire.
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
Actually 2 inches of concrete is OK. NEC 695.6 (B) (1)
I see the code pemits the use of the concrete to protectect the conductors, but I really don't believe the circuit would still be functional, if you use standard wire and 2" of concrete, after exposure to a typical building fire for an hour or so.
 

Mike01

Senior Member
Location
MidWest
2hr Cable

2hr Cable

After doing some research it turns out the cable is fire rated (1hr, 2hr, 3hr) etc. if is a special fire rated cable complying with the applicable UL standards this includes MI cable, RHW-fire rated cable, and a special MC fire rated cable, however to achieve the 2hr fire rating for the special RHW it has to be installed in conduit and per the manufacturers UL system number the way it was tested. it turns out that 2" concrete encasement is acceptable but the funny thing is that when UL does the test it tests the concrete not the cables the test is carried out without conductors installed in the pipe. interesting. but it turns out you have to use a cable listed to UL standard for the rating you are achieving and install it to the manufacturers UL System number, unless installed in a "fire rated enclosure" built to the UL standard.
 
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