There has been a consistent increase in the application of uninterruptible ac power supply (UPS) systems to continuous industrial processes which are controlled and instrumented electronically. The recent use of computer control has made this need more pronounced. In the majority of applications, static UPS equipment is being used in place of the more traditional rotating machinery in order to prevent production disasters caused by fluctuating or failing input power. The benefits of this configuration have been overshadowed somewhat by application difficulties that surfaced as more and more static UPS systems were employed. This article identifies the principal problem area, and offers solutions that have proved their worth in production operations.