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Liebert® NX UPS


For a 225-600kVA

Multi-Module Uninterruptible Power System

    1. SUMMARY

These specifications describe requirements for an Uninterruptible Power System (UPS) consisting of multiple UPS modules operating in parallel for capacity or redundancy. The UPS shall automatically maintain AC power within specified tolerances to the critical load, without interruption, during failure or deterioration of the normal power source.

The manufacturer shall design and furnish all materials and equipment to be fully compatible with electrical, environmental and space conditions at the site. It shall include all equipment to properly interface the AC power source to the intended load and shall be designed for unattended operation.

The UPS and all associated equipment and components shall be manufactured in accordance with the following applicable standards:

  • The UPS shall be UL listed per UL Standard 1778, Fourth edition, Uninterruptible Power Supplies, and shall be CSA Certified.

  • The UPS shall be provided with a Short Circuit Withstand Rating (SCWR) label denoting the maximum source fault short circuit current that is applicable to the unit. The withstand rating shall be independently verified by a nationally recognized, third-party lab.

  • The UPS shall withstand input surges to both the rectifier and bypass when configured as a dual-input unit without damage per the criteria in ANSI C62.41, category B3 (6kV). The manufacturer shall provide evidence of compliance upon request.

  • The UPS shall comply with FCC Rules and Regulations, Part 15, Subclass B, Class A. The UPS shall have a label stating FCC compliance. The manufacturer shall provide evidence and test data of compliance upon request.

  • The UPS shall be compatible with the wiring practices, materials and coding in accordance with the requirements of the National Electrical Code, OSHA and applicable local codes and standards. Provisions shall be made in the cabinets to permit installation of input, output and external control cabling using raceway or conduit for top and bottom access to input, output, bypass and DC connections. Connection cabinets shall provide for wiring gutter and wire bend radius as defined by the NEC and UL.

  • The UPS and Battery Cabinets shall be certified to the International Building Code (IBC) 2012 with seismic performance of Sds=2.27, Ip=1.5 and z/h=1.0, Optional seismic anchorage shall be available from the UPS and battery manufacturer(s) for use in compliance with this certification. The UPS module shall be pre certified by OSHPD.


      1. Design Requirements

The UPS shall be sized to provide a minimum of ____ kVA/kW output (unity load power factor rating)

The UPS shall be able to supply all required power to full rated output kVA loads with power factor from 0.7 lagging to 0.9 leading.

Load voltage and bypass line voltage shall be 480VAC, three-phase, three-wire plus ground. Input voltage shall be 480VAC, three-phase, three-wire plus ground. The AC input source and bypass input source shall each be a solidly grounded wye service except in a high resistance ground requirement (see below).

The rectifier AC input and bypass AC input may be fed from separate AC sources.

The battery shall support the UPS at 100% rated kW load for at least _____ minutes at 77°F (25°C) at startup.

The UPS shall have an active power factor-corrected IGBT converter/rectifier, capable of maintaining input power factor and input current total harmonic distortion (THDi) within specifications without an additional input filter.

The UPS shall be of transformer-free design, requiring no internal transformer in the main power path for the basic operation of the module. Optional transformers in cabinets or otherwise external to the basic UPS module shall be permissible to provide isolation and/or voltage transformation.

The UPS shall be capable of operating in a High Resistance Ground environment, and shall provide notification when a fault to ground occurs on its output. Leakage current shall not exceed 1.5 amps.
      1. Modes of Operation

The UPS shall operate as an on-line reverse transfer system in the following modes:

  1. Normal: The critical AC load shall be continuously powered by the UPS inverter. The rectifier/charger shall derive power from the utility AC source and supply DC power to the DC-DC converter, which in turn shall supply the inverter while simultaneously float charging the battery.

  2. Energy Optimization Mode (Active Eco Mode): The critical AC load shall be continuously powered by the bypass with the inverter available to power the load if the bypass source voltage or frequency exceeds adjustable parameters of power quality.

  3. Emergency: Upon failure of utility AC power, the critical AC load shall be powered by the inverter, which, without any switching, shall obtain its power from the battery plant via the DC-DC converter. There shall be no interruption in power to the critical load upon failure or restoration of the utility AC source.

  4. Recharge: Upon restoration of the utility AC source, the rectifier shall supply power to the output inverter and to the DC-DC converter, which shall simultaneously recharge the battery. This shall be an automatic function and shall cause no interruption to the critical AC load.

  5. Bypass: If the UPS must be taken out of service for maintenance or repair, the bypass static switch shall transfer the load to the bypass source. The transfer process shall cause no interruption in power to the critical AC load. An optional external wrap-around maintenance bypass shall be used to ensure full isolation of the unit for the service of internal components while providing safety from arc flash and in compliance with OSHA requirements.

  6. Off-Battery: If the battery only is taken out of service for maintenance, it shall be disconnected from the DC DC converter by means of an external disconnect circuit breaker. The UPS shall continue to function and meet all of the specified steady-state performance criteria, except for the power outage backup time capability. If multiple battery strings are used, each string shall be capable of being electrically isolated for safety during maintenance.
      1. Performance Requirements

The solid-state power components, magnetics, electronic devices and overcurrent protection devices shall operate within the manufacturer’s recommended temperature when the UPS is operating at 100% critical load and maintain battery charging with either of the following conditions occurring:

  • Any altitude within the specified operating range up to 3300 ft. (1000m) elevation

  • Any ambient temperature within the specified operating range of 32°F to 104°F (0°C to 40°C)
      1. Input

  1. Voltage: Input/output voltage specifications of the UPS shall be:

  • Rectifier AC Input: 480V, three-phase, three-wire-plus-ground

  • Bypass AC Input: 480V, three-phase, three-wire-plus-ground

  • AC Output: 480V, three-phase, three-wire-plus-ground

  1. Voltage Range: +10%, -30% of nominal (minimum -15% at nominal load.) The UPS shall operate without discharging the battery at 70% of full nominal load with voltage down to -30% of nominal.

  2. Frequency Range: 60Hz, adjustable by service personnel up to ±3.6Hz in 0.12Hz increments

  3. Rectifier Walk-In: 0% to 100% of full rated load over 2.5-90 seconds (adjustable) with full rectifier power.

  4. Rectifier Start Delay: Programmable from 1-180 seconds

  5. Max Inrush Current: UPS inrush current not to exceed 1.5 times rated input current.

  6. Power Factor: Minimum 0.99 at full load with nominal input voltage

  7. Current Distortion: Less than 3% input current THD at rated load and nominal voltage in double-conversion mode

  8. Surge Protection: Sustains input surges without damage per criteria listed in ANSI C62.41, category B3 (6kV)

  9. Short Circuit Current Withstand Rating: Units shall carry as standard 100 kA Short Circuit Withstand Rating (SCWR). All ratings shall be certified and a label shall be applied to the unit clearly identifying this rating as required by the National Electrical Code.

      1. AC Output

  1. Load Rating: 100% load rating at 104°F (40°C) for 8 hours for any load from 0.9 leading to 0.7 lagging; 100% of load rating continuous at 95°F (35°C).

  1. Voltage Regulation:

  • ±1% RMS average for a balanced three-phase load

  • ±3% for 100% unbalanced load for line-to-line imbalances

  1. Voltage Adjustment Range: ±5% for line drop compensation adjustable by factory service personnel.

  2. Frequency Regulation:

  • Synchronized to bypass: ±1.2Hz default setting, adjustable by factory service personnel)

  • Synchronized to internal clock 0.06Hz

  1. Efficiency: Defined as output kW/input kW at rated lagging load power factor; and not less than the values listed below (Select kVA rating for this specification. Values are for single modules.):

    kVA Rating

    25% Load


    75% Load

    100% Load































  2. Phase Imbalance:

  • Balanced loads 120° ±1°

  • 100% unbalanced loads 120° ±3°

  1. Voltage Transients (average of all three phases):

  • 0-100% or 100-0%

Response: Meets IEC 62040-3: 2010 Figure 2 Curve 1, Class 1

Meets ITIC and CBEMA Curve Requirements

  • 10-100% or 100-10%

Transient Voltage Deviation, RMS: ≤5%

Step Load Transient Recovery (linear loads) ±1% of nominal within four line cycles

  1. Voltage Harmonic Distortion:

  • Maximum 1% RMS total (100% resistive load)

  1. Overload at Full Output Voltage with ±1% Voltage Regulation:

  • 100% continuously

  • 125% of full load for 10 minutes at 95°F (35°C) ambient

  • 150% of full load for a minimum of 60 seconds at 95°F (35°C) ambient

  1. Current Limit: 300% nominal current including a bolted fault condition without bypass for up to 10 milliseconds and 150% for <5 seconds.

  2. Fault Clearing:

  • Inverter only: 200% of normal full load current for 200 milliseconds or 150% of normal full load current for <5 seconds (when bypass is not available).

  • Bypass available: 500% for 600 milliseconds operation when bypass is available.

  • The UPS shall supply current from both the bypass and the inverter until the inverter overload time expires, and then shall continue to supply current from the bypass to clear the fault.
      1. Grounding

The UPS chassis shall have an equipment ground terminal.
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