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UL 1778-2017 pdf free download
UL 1778-2017 pdf free download.Uninterruptible Power Systems.
AAA.5.2.1 Mechanical isolation means shall be provided for servicing the power supply where failure of or leakage through a solid-state device could result in transfer of energy between two or more power sources, The disconnecting means shall be provided as an integral part of the equipment and be connected into the Circuit Ifl such a way that when opened it will prevent transfer of energy between the different power sources. To facilitate servicing, barriers (or other suitable means) and/or marking shall be provided for protecting SERVICE PERSONNEL from live parts located ahead of isolating switches.
AAA.5.2.2 Automatic mechanical isolating means shall be provided as an integral part of the equipment to prevent transfer of energy from a single-branch private supply system (such as a battery and inverter) to a branch of a multibranch system (such as a PRIMARY POWER system) upon loss or shutdown of the PRIMARY POWER system unless BACKFEEO is not possible when evaluated in accordance with AAA.5.1.1. The isolating means may be a relay. contactor, motorized circuit breaker, or other device with an air gap between contacts.
AAA.5.3. 1 Static transfer switches shall be tested as part of the equipment to determine their acceptability for the application.
AAA.5.3.2 Compliance with the requirements of AAA.5.1.1 shall be verified by shorting one power switching component (e.g., SCIR) and placing one fault on another component, such as in the control circuit. The fault placed on the component shall simulate the failure mode of that component (e.g., cathode to anode short on SCR, emitter to collector short or open on a transistor, or welding of a relay contact in the control circuit). This analysis shall be performed first with the PRiMARY POWER supply energized and repeated with the PRIMARY POWER supply not energized.
AAA.5.3.3 The electric strength test shall be performed on a static transfer switch with the solid-state devices, or assemblies, normally connected between the systems disconnected.
AAA.6 Transfer switches
AAA.6.1 Failure of a mechanical transfer switch shall not result in transfer of energy from a single-branch private supply system (such as a battery and inverter) upon loss or shutdown of the multibranch system (such as a PRiMARY POWER system). A failure analysis of the mechanical transfer switch shall not be required if the current through the contacts is the same or less than the RATED CURRENT of the switch and the overload test evaluation is performed at six times the RATED CURRENT. The control circuit that operates the mechanical transfer switch shall be subjected to a failure analysis.
AAA.6.2 A ivss switch or maintenance BYPASS used to connect the protected load directly to the BYPASS source shall comply with the requirements of AAA.6.3.
AAA.6.3 A BYPASS switch or maintenance BYPASS, when tested in conjunction with a UPS, shall comply with the load transfer test specified in AAA.7 and the applicable requirements of this Standard.UL 1778-2017 pdf free download.
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