Wednesday, February 22, 2012
Inside the elevator, the ninja sees a camera that he wants to turn off. He shorts out the circuit to the camera, intending to trip the breaker and killing power to the camera. But what happens is that he trips the breaker for the entire building. The elevator comes to a halt and the ninja is trapped.
The name for this scenario is “system coordination.” When an electrical system is coordinated, a short on a small circuit will trip the breaker for that circuit, but not the breakers for the larger circuits. This coordination contains the power outage to a small area in the building.
In this building, the breakers for the elevator were not coordinated. Shorting the small circuit also tripped the main building breaker. As any good electrical engineer knows, the National Electrical Code requires coordinated circuit breakers for elevators in order to avoid the situation the ninja encountered. One can only imagine the desperate fate of the electrical engineer who designed this building when the ninja escapes his new found captivity!
Mark Robison, PE
