He pointed up. The cable tray was a spaghetti bowl of a dozen other power cables, all running together for fifty meters in the hot, dusty ceiling. Above that, a steam pipe from the boiler room leaked a faint haze of heat.
“Three things kill a cable’s capacity. First, . You bundle six hot cables together, they trap each other’s heat. You have to ‘derate’—reduce the allowable current by maybe 30, 40 percent. Second, ambient temperature . This ceiling is 45 degrees, not 30. That leaves less ‘temperature budget’ for the cable’s own heat. Third, installation method —buried in insulation, in conduit, on a tray? All different.” cable size current carrying capacity
He handed her a worn copy of the electrical code, dog-eared at the ampacity tables. He pointed up
“She got too hot, didn’t she, Marco?” asked Lena, the new junior engineer. She held the specs in her hand, fresh from the office upstairs. “Three things kill a cable’s capacity