“Exactly,” said Leo. “That breaker isn’t a protection device anymore. It’s a bomb. When that 72 kA fault occurs, the breaker will try to open, but the arc inside will be so violent it will vaporize the contacts, explode the casing, and turn the panel into a fireball. You won’t have a ‘short circuit.’ You’ll have a ‘long explosion.’”
“See that?” Leo said, pointing at the darkened but intact panel. “That’s the sound of a proper calculation. A ‘sneeze,’ not a ‘heart attack.’”
She looked at the existing switchgear’s label: Rated short-circuit withstand: 25 kA for 1 second. Rated peak: 52 kA.
Old Leo, sipping his third coffee, chuckled. “Let me tell you a story.”
[ I_{SC} = \frac{I_{Full\ Load}}{Z_{pu}} ]
“We are toast,” she said. “The breaker will explode before it even trips.”