Chapter 3 Parallel Ups Installation And Commissioning; Features; Requirements; Connecting Power Cables - Liebert NXC User Manual

Liebert NXC Parallel UPS Installation and Commissioning
Chapter 3 Parallel UPS Installation And Commissioning
This chapter introduces the features, requirements, installation and commissioning of the parallel system.
The UPS parallel system provides the user with N + X (2 ≤ N + X ≤ 4) parallel configuration, N stands for the basic parallel sets, X
stands for the redundant sets.

3.1 Features

1. The software and the hardware of each UPS in parallel system are the same as those of the single UPS. The basic parameters
of the parallel system can be set through the LCD (Refer to 3.4.2 for the details), and the detailed parameters can be set
through the service software (For service engineers only). For all UPSs of the parallel system, the requirements of the parameter
settings are same.
2. The parallel cables form a ring connection (Refer to 3.3.2 for details) to provide reliability and redundancy for system. The
intelligent parallel logic provides the user with maximum flexibility. For example, the each UPS in the parallel system can be
switched off or on in random order; seamless transfer can be achieved between Normal mode and Bypass mode, and the
transfer is automatically recoverable: that is, after the overload condition is removed, the system will return to the original
operation mode automatically.
3. The total load of the parallel system can be queried through the LCD of each UPS.

3.2 Requirements

A UPS system composed of multiple parallel-connected UPS units is equivalent to a large UPS system. Nevertheless, it provides
increased system reliability. To ensure equal utilization of all UPS units and compliance with relevant wiring regulations, the
following requirements must be met:
1. All single UPSs must have the same capacity and must be connected to the same bypass source.
2. The bypass input power and rectifier input power must be connected to the same neutral line input terminal.
3. If a residual current detector (RCD) is required, it must be set correctly and installed before the same neutral line input
terminal, or it must monitor the protective earth current of the system. Refer to Safety Manual.
4. The outputs of all single UPSs must be connected to the same output bus.
5. As the UPS parallel system is not fitted with any auxiliary contact detection devices for the UPS unit output LBS (Load Break
Switch) or maintenance bypass LBS. Removing the single UPS from the parallel system before maintenance and adding the
single UPS into the parallel system after maintenance must be conducted strictly following the procedures provided in 5.2.
Failure to observe this may affect the load power supply reliability.

3.3 Connecting Power Cables

Each single UPS of the parallel system need to configure the MCB and cable respectively, refer to 2.4 for the specification.
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