The uninterruptible power system (UPS) acceptance test is a comprehensive electrical and functional inspection performed on a new or reconditioned UPS unit to verify that the system's inverter, static transfer switch, bypass circuitry, and control logic are all installed correctly and operate within the nameplate ratings and design specifications. The test covers input and output voltage stability, the static-transfer sequence between inverter and bypass, the oscillator's free-running frequency, the DC-undervoltage trip point on the inverter's input breaker, and alarm and synchronizing-indicator function - essentially confirming that the UPS will do what its nameplate and control scheme promise to do when called upon during a utility interruption. The battery, and any UPS-integrated breakers, automatic transfer switches, and rotating machinery, are tested under their own equipment-specific sections and cross-referenced from this test rather than repeated here. NETA ATS-2025 lists this as a mandatory electrical test item for all three-phase and single-phase UPS equipment before first energization.
A UPS is installed to bridge the gap between a utility outage and generator startup, or to provide ride-through time for a load to shut down cleanly. If the UPS transfer logic is miswired, the static switch cannot transition load between inverter and bypass, the oscillator frequency drifts outside the manufacturer's tolerance, or the DC-undervoltage protection fails to trip the inverter's input breaker before the battery is damaged, the system will fail at the moment it is most needed - when the utility actually goes down. A comprehensive acceptance test before energization verifies that none of those failure modes are present and that the unit responds to the command signals and protective thresholds it will rely on in production.
Acceptance: run before a new or reconditioned UPS is first energized and connected to its load circuit, as part of the standard electrical test sequence. The test includes a functional verification of the static-transfer and control logic at the manufacturing or shop site, before the unit is shipped or installed in its final location. If a UPS must be moved, re-rated, or reconfigured in the field, a follow-up acceptance test on the revised configuration is performed before re-energization.
With the UPS de-energized and isolated per the shop's safety procedures, the unit's input and output terminals are verified for correctness of polarity and phase sequence, and the nameplate ratings (voltage, frequency, kVA capacity, input/output phase count) are recorded against the equipment-specification document. Bolted electrical connections are checked for tightness. The UPS is then energized from a stable AC mains source with input voltage and frequency confirmed at or near nameplate rating. The oscillator's free-running frequency is measured and compared against the manufacturer's published tolerance. A static-transfer test moves the load from inverter to bypass and back, normally under load if the site permits, confirming the transfer completes without an unacceptable disturbance to the output. The DC-undervoltage trip function is exercised by driving the DC bus toward the manufacturer's published trip setting and confirming that the inverter's input breaker opens at that point. Alarm circuits and the synchronizing indicators for the static switch and bypass switch are tested for correct operation. Finally, the settings of protection devices are coordinated with upstream breakers, and the UPS's battery, along with any integrated transfer switches, breakers, or rotating machinery, is tested per its own governing section and referenced here rather than retested.
Equipment identification (manufacturer, model, serial number, nameplate kVA rating, input voltage, output voltage, phase count, frequency, and equipment designation) captured at the outset; bolted-connection resistance readings; input voltage and frequency readings during steady-state normal operation; the oscillator's measured free-running frequency against the manufacturer's published tolerance; the static-transfer test result (inverter to bypass and back) and the load condition under which it was performed; the DC-undervoltage trip setting and the measured value at which the inverter's input breaker tripped; the results of the alarm-circuit and synchronizing-indicator tests; and the make, model, serial number, and calibration-due date of all test instruments used. Results of the cross-referenced battery, breaker, automatic-transfer-switch, and rotating-machinery tests are captured under their own test records and referenced by report number.
NETA ATS-2025 7.22.2 specifies that bolted-connection resistance is compared against similar connections, and that the static transfer between inverter and bypass, the oscillator's free-running frequency, the DC-undervoltage trip function, alarm circuits, and the synchronizing indicators must each function in accordance with the manufacturer's published data and the system's design requirements; the DC-undervoltage trip must open the inverter's input breaker at the manufacturer's specified setting. All test results are recorded and compared against the equipment nameplate and the control-system design documentation; any result outside the manufacturer's tolerance band or the project specification is flagged for investigation and corrective action before the unit is released to service. The battery, and any UPS-integrated breakers, automatic transfer switches, or rotating machinery, are evaluated against the acceptance criteria of their own governing sections rather than a criterion specific to this test. See the purchased NETA ATS-2025 standard for the complete acceptance criteria and any load-profile-specific requirements.
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