By their very nature, power systems are dynamic. They evolve and change over time. Every passing year sees the gradual decrease of reserve capacity and response time, as well as the slow erosion of insulation and contacts. More importantly, every new load, upgrade, expansion, and reconfiguration creates unexpected stresses and interactions that the original power system was not designed to address.To further complicate the situation, the proliferation of computers and other microchip technologies, and the advent of utility deregulation, make the challenges of maintaining a safe, efficient, and reliable power system more complex and daunting then ever before. System ReliabilityWith so many issues to consider, how can a facilities manager assure the reliability of a system? The best place to start is by having a current one-line diagram of the electrical system. This should be a comprehensive document that incorporates the entire system, including information on the original system and changes and expansions that have occurred. If the one-line diagram is not currently available, it is not difficult to develop. An experienced engineer – in design, protection, and coordination of power systems – can easily gather the necessary information by walking through the facility.From the information provided in a current comprehensive one-line diagram, a power system engineer can evaluate the electrical system for potential problems and identify areas of concern. These areas of concern can be addressed more specifically through a power systems study.