Dual sources of normal power shall be considered but

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Dual sources of normal power shall be considered but shall not constitute an alternate source of power Distribution system arrangements shall be designed to minimize interruptions to the electrical systems due to internal failures by the use of adequately rated equipment The following factors shall be considered in the design of the distribution system: Abnormal voltages such as single phasing of three-phase utilization equipment, switching and/or lightning surges, voltage reductions, and so forth Capability of achieving the fastest possible restoration of any given circuit(s) after clearing a fault Effects of future changes, such as increased loading and/or supply capacity Stability and power capability of the prime mover during and after abnormal conditions Sequence reconnection of loads to avoid large current inrushes that trip overcurrent devices or overload the generator(s) Bypass arrangements to permit testing and maintenance of system components that could not otherwise be maintained without disruption of important hospital functions Effects of any harmonic currents on neutral conductors and equipment Current-sensing devices, phase and ground, shall be selected to minimize the extent of interruption to the electrical system due to abnormal current caused by overload and/or short circuits Generator load-shed circuits designed for the purpose of load reduction or for load priority systems shall not shed life safety branch loads, critical branch loads serving critical care areas, medical air compressors, medical-surgical vacuum pumps, pressure maintenance (jockey) pump(s) for water- based fire protection systems, generator fuel pumps or other generator accessories Essential electrical systems shall have a minimum of two independent sources of power: a normal source generally supplying the entire electrical system and one or more alternate sources for use when the normal source is interrupted Where the normal source consists of generating units on the premises, the alternate source shall be either another generating set or an external utility service ESS Type 1 systems are required to have a minimum of two independent sources of electrical power. A normal source that generally supplies the entire facility and one or more alternate sources that supply power when the normal source is interrupted. The alternate source(s) must be an on-site generator driven by a prime mover unless a generator(s) exists as the normal power source. In the case where a generator(s) is utilized as the normal source, it is permissible for the alternate source to be a utility feed. Alternate source generators must be classified as Type 10, Class X, Level 1 generator sets per NFPA 110 2-2 capable of providing power to the load in a maximum of 10 seconds.
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