My understanding for an ENT conduit (other than for future flexibility) was that it was fire-rated, to reduce the spread of fire/air-flow between floors. If the conduit went through fire-blocks or floors, holes would have to be sealed with fire-retardant sealant/caulking.

But I always come across images like this:
enter image description here
or this:
enter image description here

Note the low-voltage backless gang boxes.
Doesn't the backless gang box defeat the purpose of fire blocking? If a fire starts in that section, it has no obstruction to enter the ENT conduit (through the backless gang box) and go all the way wherever the conduit leads to? What was the point of sealing off the floor/fire-block hole then?

2 Answers 2


I'm not a fire expert, but I doubt fire will actually spread through the conduit. Toxic fumes, sure, but not fire (unless the conduit is really short). Flames will, however, quickly jump through a hole in a 1 1/2" - 3" thick barrier.

If you really want to take fireblocking to the extreme, you could seal the ends of the conduit around the cables with fireblocking material.

  • 2
    When working in a gas refinery, that is exactly what was done when fireblocking.
    – diceless
    Commented Aug 14, 2015 at 20:12

Any plastic type back boxes should be lined on the external side with fire resisting material. A fire resisting putty is available for metal back boxes you should not use open back boxes in fire walls. seal the open end of conduits with FR putty

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.