![]() However, one transfer switch shall be permitted in a facility with a maximum demand on the essential electrical system of 150 kVA or less. Each branch on the emergency system and equipment system, respectively, shall have one or more transfer switches to serve the system loads. The number of transfer switches used "shall be based on reliability, design, and load considerations" in accordance with NEC Article 517.30(B)(4). Health care facilities (NEC Article 517): Essential electrical systems for hospitals consist of the emergency system and equipment system to supply a limited amount of lighting and power essential for life safety and effective hospital operation when the normal service is disconnected. Transfer equipment shall be designed and installed to prevent inadvertent, simultaneous connection of primary and secondary supplies of power. Transfer equipment, including transfer switches, are required to be automatic and identified for standby use. NFPA 1600-2013: Standard on Disaster/Emergency Management and Business Continuity Programs contains further information on this topic. These systems may include power systems, HVAC, fire alarm, security, and communications in these areas. The requirement to comply with NEC Article 708 is provided by any governmental agency having jurisdiction or by a facility providing documentation establishing the necessity for such a system. There are no code requirements for power to be transferred to the secondary source within a certain time frame.Ĭritical operations power systems (COPS) (NEC Article 708): Interruptions or outages to designated critical operations areas may negatively impact national security, economy, public health, or safety. However, transfer equipment shall be designed and installed to prevent inadvertent, simultaneous connection of primary and secondary supplies of power. Transfer equipment, including transfer switches, for optional standby systems are not restricted to the same requirements as emergency and legally required system transfer equipment. Optional standby systems (NEC Article 702): Optional standby systems are defined by the NFPA as "intended to supply power to public or private facilities or property where life safety does not depend on the performance of the system." These systems may include data processing and communication systems, and mission critical systems that are not legally required by the AHJ. Power must be transferred to the secondary source in 60 sec or less. Transfer equipment, including transfer switches, are required to be automatic, identified for standby use, and approved by the AHJ. Legally required standby systems (NEC Article 701): Legally required standby systems are defined by the NFPA as "intended to automatically supply power to selected loads (other than those classed as emergency systems) in the event of failure of the normal source." These systems may include heating and refrigeration systems, communications systems, ventilation and smoke removal systems, and other processes that, when stopped in the event of primary source interruption, could create hazards or hamper rescue or firefighting operations. Power must be transferred to the secondary source in 10 sec or less. Transfer equipment shall supply only emergency system loads. ![]() Transfer equipment, including transfer switches, are required to be automatic, identified for emergency use, and approved by the authority having jurisdiction (AHJ). Standby system types include emergency systems, legally required standby systems, optional standby systems, critical operations power systems (COPS), and systems that support health care facilities (see Figure 1).Įmergency systems (NEC Article 700): Emergency systems are defined by the NFPA as "intended to automatically supply illumination, power, or both, to designated areas and equipment in the event of failure of the normal supply or in the event of accident to elements of a system intended to supply, distribute, and control power and illumination essential for safety to human life." These systems may include fire detection and alarm systems, elevators, fire pumps, and egress lighting.
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