Ampacities for Cables in Randomly Filled Trays

The allowable current which may be carried by a given conductor size cable has been thoroughly investigated in almost every conceivable type of cable installation. One area which has not had much attention up to now is the allowable current which can be carried by cables in cable trays, or troughs. This paper presents a completely general method for calculating the ampacities of cables in cable trays; it has been derived from elementary heat transfer theory and amply verified with many full-scale tests. The method shows that currently published ampacities for small cables in highly filled trays must be reduced, but the large cable ampacities can be safely increased.