Reliability is an important design criterion. Service capacity adequate to supply the load is not sufficient for many facilities. Hospitals, data centers, and other critical facilities require high availability of electrical power and use a combination of multiple sources and redundant pathways to maintain service in the event of utility failure or an internal fault.
The boom in the construction of mission-critical facilities during the recent dotcom era popularized computer software packages that analyze power system reliability, given configuration and information about the failure characteristics of the components. Because switchgear, transformers, and generators are expensive, increasing redundancy to obtain higher levels of reliability carries a price tag, and such software is often used to determine the economically optimal configuration.