simplicity reasons, most circuit (overcurrent) protection and power quality control (voltage regulation) devices used by electric utility companies are designed with the assumption that power always flows in one direction. An interconnection agreement can be arranged for equipment designed to backfeed from the consumer's equipment to the electrical utility provider's distribution system. This type of interconnection can involve nontrivial engineering and usage of costly specialized equipment designed to keep distribution circuits and equipment properly protected. Such costs may be minimized by limiting distributed generation capacity to less than that which is consumed locally, and guaranteeing this condition by installing a reverse-power cutoff relay that opens if backfeeding occurs. Safety and operational hazards Because it involves transfer of significant amounts of energy, backfeeding must be carefully controlled and monitored. Personnel working on equipment subject to backfeeding must be aware of all possible power sources, and follow systematic protocols to ensure that equipment is fully de-energized before commencing work, or use special equipment and techniques suitable for working on live equipment. When working on de-energized power conductors, lineworkers attach temporary protective grounding assemblies or "protective ground sets", which short all conductors to each other and to an earth ground. This ensures that no wires can become energized, whether by accidental switching or by unintentional backfeeding. Because of the hazards presented by unintentional backfeeding, the usage of equipment that defeats engineered or standardized safety mechanisms such as double-ended power cords (an electrical cord that has a male electrical plug on both ends) is illegal and against the United States National Electrical Code. See also Islanding, a similar phenomenon involving local generators. Transfer switch References Electric power distribution