Last edited 22 Apr 2021

Uninterrupted power supply for buildings

An uninterrupted power supply (UPS), sometimes referred to as an uninterruptible, or uninterruptable power supply, provides an alternative ‘no-break’ electrical supply that can be required in situations where it is important there is no loss of electrical supply, even if the primary supply fails.

Typically this is necessary where a loss of power could result in a risk to health or disruption to business, for example:

Emergency services and medical facilities.
Leisure and sports venues where scheduled and ticketed events take place.
Data centres.
Financial services.
Some industrial processes.

It might also be necessary to support specific critical services, such as:

Information and communications technology (ICT).
Emergency lighting.
Fire alarms and other safety systems.

UPS can be also be useful when the primary power source is shut down intentionally, for example during maintenance, and some systems can correct power supply issues such as voltage spikes.

A UPS is not the same as an auxiliary, standby or emergency power supply as it provides virtually instantaneous supply, avoiding any power interruption.

Generally this will include the use of batteries, supercapacitors, or flywheels (rotary UPS) that either allow equipment to be powered down safely when the mains supply is interrupted, or provide power for long enough for an auxiliary supply to come online. This may only take a few minutes.

Auxiliary power might be provided by:

Simple packaged battery units that can be incorporated into equipment such as comms cabinets.
Stand-alone battery units.
Standby generators.

They might be very small units that supply a single computer, to large installations that supply a major industrial process.

UPS systems will generally include some form of automatic mains failure detection (AMF) and an automated changeover process. They may also detect power restoration and automatically revert to the mains supply.

If continued power supply is critical, the UPS may be provided by a number of smaller packaged units, rather than by a single source, which might introduce a potential source of failure itself. The packaged units might include some ‘redundancy’ so that if one or more of the units fail, there is still adequate supply.

UPS require careful design, particularly where they are supplying critical systems. Regular maintenance is necessary to ensure continued performance.