When designing for horizontal pathways in an environment that requires fire-stopping for penetrating a rated wall, what is the MAXIMUM till ratio for telecommunications cabling in a cable tray?

Question

Options

• A20 percent
• B40 percent
• C50 percent
• DThere is no fill ratio for cable tray

• A
  4% (1)
• B
  81% (22)
• C
  4% (1)
• D
  11% (3)

Explanation

When telecommunications cable trays penetrate a fire-rated wall, the maximum allowable fill ratio is 40 percent, as required to ensure that approved fire-stop materials can be properly installed around the cables and within the tray to maintain the wall's fire rating integrity.

Option A (20 percent) is incorrect because it is overly restrictive and not the standard specified for this application. Option C (50 percent) is a common fill ratio referenced for general cable tray installations, but it does not account for the added requirement of accommodating fire-stopping compounds at rated wall penetrations. Option D is incorrect because fire-stopping requirements do impose a fill limit precisely to ensure the intumescent or sealant material can fully encapsulate the cables and seal the opening effectively.

Memory tip: Associate "40 for fire" - when a wall is rated, you drop from the general 50 percent fill guidance down to 40 percent to leave room for the fire-stop material to do its job.

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