Fire Rated Cables in Conduit

Mineral Insulated Cable, of course, does not need to be installed in a conduit as the copper sheath is already a proven solution to provide up to 3 hour escape time in ‘Real World’ fire conditions.

The Problem with Conduits 

However, installing cables inside galvanized steel conduit is a very common way to provide mechanical protection for circuits or parts of circuits, but what is not commonly known is that Fire Rated cables should not be run inside galvanized steel conduits.

The problem was first identified by UL (Underwriters Laboratories) in 2012 and subsequently UL removed all approvals for flexible fire rated cables installed in galvanized steel conduit in the USA and ULC did likewise in Canada.

The reason UL removed the listings can be explained as follows:

UL received information that the zinc in the galvanised conduit can affect the cables fire rating. The concern regarding performance of these products is that the presence of zinc (galvanization) can compromise the cable circuit integrity at high temperatures because of the reaction of the zinc with the copper conductor which at the high temperatures in fires will form brass. This effect was validated by Underwriters Laboratories and as a result of this validation, UL and ULC revised the guide information and individual certifications to exclude the use of zinc (galvanised) components with Fire Resistant cables.

During further research on a wide array of products, including conduits without zinc interior coating, it was found that Fire Resistant cables were also not able to consistently achieve the required 2-hour fire-resistive rating.

In the UK installing Fire Rated cables in steel conduit is not yet excluded by regulation but manufacturers of Fire Rated cables sold in UK are required to test and certify them to respective British Standards. Currently, in the UK, none of the BSI test standards actually require the fire rated cables to be tested in the mounting configurations they are normally installed.


Read our whitepaper on this topic here: Don't Install Fire Rated Cable in Conduit 

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