“Current-carrying capacity isn’t just about the copper,” Marco said. “It’s about getting rid of the heat the copper makes. Resistance creates heat. Every electron squeezing through that wire is like a runner in a tunnel. The more runners, the more heat. The insulation can only take so much before it gives up—usually 70, 90, or 105 degrees Celsius, depending on the type.”
“Rule one,” he said. “Respect the derating factors. Rule two—there is no rule two. Just don’t trust a cable in a vacuum.” cable size current carrying capacity
“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. Every electron squeezing through that wire is like
Marco did the math in his head. “Grouping factor for twelve cables? 0.5. Temperature correction for 45°C? About 0.8. Multiply those. 100 amps times 0.5 times 0.8 is… 40 amps. You were running 85. You weren’t ‘within the number.’ You were running more than double what that cable could handle. It didn’t trip the breaker because the breaker is also hot, and its own calibration drifted. But the cable? It cooked.” “Respect the derating factors