Emergency/Standby Generator
CSI Division 26, Electrical
An engine-driven generator, typically diesel or natural gas, installed to automatically provide backup electrical power to a building during a utility outage, sized to carry either the whole building's load or a smaller, code-defined subset of life-safety and critical loads, and connected through an automatic transfer switch that detects the outage and switches the building's power source.
Why it matters
Code distinguishes between an emergency system, required life-safety loads, such as exit lighting and fire alarm systems, that must be powered within seconds, and a standby system, other critical loads that can tolerate a longer transfer time, and a generator's sizing and transfer switch configuration have to match which category of loads it's actually serving.
On a real project
A hospital's emergency generator is sized and configured to restore power to its life-safety loads within the ten-second window code requires, with a separate, larger standby generator covering less time-critical loads like general HVAC on a longer transfer sequence.
Who this matters most to
An Electrician installs the generator's electrical connections and the automatic transfer switch. A MEP Engineer designs which loads the generator serves and the required transfer time for each category.
Where this goes wrong
A contractor wires several general building loads into a circuit intended only for code-required life-safety loads on the emergency generator, exceeding the generator's designed capacity for that circuit. During the required annual load-bank test, the overloaded emergency circuit trips under full life-safety load, and the electrical inspector flags the miswired circuit before it's ever needed during a real outage.