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Spacing of Through Penetration Firestop system

Darren Emery

Darren Emery

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Oct 20, 2009
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Manhattan, Ks
If memory serves (and I'll be the first to admit it doesn't always serve me well these days) I found an answer to this question many years ago, but having no luck currently. I believe the answer may be found deep in the details of the associated UL testing procedure. Any input would be appreciated.

Given a properly designed TPFS to allow 4/0 SER cables to penetrate a 2 hour wall, and a max cable bundle diameter of 4" ( with 4/0 - max two per hole), and a total of 7 SER cables to run through the wall, where would I find the minimum separation distance between penetrations?

I know in theory, if you install the system properly, it should be as if there is no opening in the wall. But the idea of all 7 conductors right next to each other, in a single floor joist cavity, turning this particular portion of the rated wall into swiss cheese, just doesn't seem right to me.
 
Can you describe the method proposed for the through penetration?

I have seen sections of ridged conduit with the ends sealed by intumescent material. The pipe was long….perhaps ten feet on each side of the rated wall. Hilti rings were placed at the wall. I don’t recall a particular spacing and I suppose it would be determined by the physical characteristics of the building. As I recall, the system was something that the contractor and I came up with but I might be wrong about that. It was a long time ago.

Thinking about it I seem to recall that it was a single cable per pipe. Anyway it was probably overkill and there is a reasonable solution in today’s world.
 
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For fire barriers I believe there is a limit of 100sqin per 100 sqft...if that is what you are looking for? Anything other that that would be in the penetration listing, just make sure you are getting the whole listing, not just a cut sheet...
 
Maybe i was remembering the electrical boxes....

714.4.2 Membrane penetrations. Membrane penetrations
shall comply with Section 714.4.1. Where walls or
partitions are required to have a fire-resistance rating,
recessed fixtures shall be installed such that the required
fire resistance will not be reduced.
Exceptions:
1. Membrane penetrations of maximum 2-hour
fire-resistance-rated walls and partitions by
steel electrical boxes that do not exceed 16
square inches (0.0 103 m2) in area, provided
that the aggregate area of the openings through
the membrane does not exceed 100 square
inches (0.0645 m2) in any 100 square feet (9.29
m2) of wall area. The annular space between
the wall membrane and the box shall not
exceed 1/8 inch (3.2 mm). Such boxes on opposite
sides of the wall or partition shall be
separated by one of the following:
 
Full listing from UL. Indeed. Has anyone else found the "ever improving" UL website a nightmare to navigate? So far...I cannot find the full report :(
 
TheCommish said:
In accordance wiht the manufacturs listing sheet and conditions, each assemble has minimum and maximums, for all the conditions it is approved for
Click to expand...
Agreed - minimum and maximums per penetration, but I cannot find how many different penetrations can be allowed in a given area of a 2 hour wall. For example, in a given floor joist cavity (say 12" by 16") how many times can I cut hole in the wall in this space, and use an approved TPFS for SER cable?

If I do more than 3-4, it's going to look like swiss cheese.

The 3M rep I contacted did his best to be helpful, but could only suggest leaving a "reasonable" amount of drywall between each hole. 1/2" or so should be good...
 
I would look for a different system if I need multiple holes, ask technical assistance not the sales person.

As an inspector if the holes were closely space I would require tech data to support the instillation, closely space less then the diameter of the largest hole.
 
Darren Emery said:
in a given floor joist cavity (say 12" by 16") how many times can I cut hole in the wall in this space
Click to expand...
You need 7 for seven 4/0 SER cables. At 2" there is plenty of room. I can't say if there is a structural issue. As to proximity to each other....if there is drywall, it should remain intact so the more the better.
 
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