Uninterruptible Power Supply (UPS)
CSI Division 26, Electrical
A battery-backed electrical system that provides instantaneous, gap-free backup power to critical equipment, such as servers or medical devices, bridging the brief gap between a utility outage and a standby generator actually starting and coming online, distinct from a generator since a UPS responds in milliseconds rather than seconds.
Why it matters
A generator alone still has a startup delay of several seconds before it can supply power, long enough to crash a server or interrupt a sensitive piece of medical equipment, a UPS is what covers that gap, and equipment that genuinely can't tolerate any interruption at all needs both a UPS and a generator working together, not one or the other.
On a real project
A data center's servers are protected by a UPS that instantly takes over the electrical load the moment utility power drops, holding the load until the facility's standby generator starts and comes fully online several seconds later.
Who this matters most to
An Electrician installs the UPS and its battery system. A MEP Engineer sizes the UPS's battery runtime specifically to bridge the generator's actual startup and transfer time.
Where this goes wrong
A facility installs a UPS sized only for a brief, generic runtime without confirming it actually covers the specific standby generator's real startup time. During an actual outage, the generator takes longer to reach full capacity than assumed, the UPS batteries deplete before the generator can take over, and critical equipment loses power anyway despite the UPS being in place.