Ampacity of cables in trays surrounded with fire barrier material

A computer program that is capable of calculating the ampacity of cables in a single tray that is surrounded by a fire barrier system is described, The program is used to determine the effect of the fire barrier design on the ampacity of the cables for a wide variety of cable, tray and fire barrier conditions. The calculated ampacity values are compared to values published in the ICEA/NEMA P54-440 resulting in a fire barrier ampacity correction factor. This factor is convenient and simple to use, because it quantitatively shows how much the conductor current must be reduced when the tray is surrounded by fire barrier material. Ampacity correction factors are provided for different fire barrier thicknesses with differing thermal resistivities. The program is also used to perform a sensitivity study so that those conditions which most greatly affect the cable ampacity can be identified. Results predicted by the program are compared to data measured during an extensive experimental test program carried out by TVA. The computer-predicted ampacity values and tray temperatures are shown to compare well with values measured during the test program.