Chapter 4 Operations 39
LIEBERT APM UPS Module And Parallel System 30kVA~150kVA User Manual
5.2.2 Parallel Requirements Of UPS Rack Systems
A group of paralleled UPS Rack Systems behave as if it were one large UPS with the advantage of presenting higher
reliability and/or higher total output power.
The following requirements apply:
1. All UPS Rack Systems must be connected to the same bypass source (i.e: must be in phase and have the same
neutral reference)
2. The bypass and the main input sources of each UPD rack unit must be referenced to the same neutral potential.
3. Any RCD (Residual Current detecting device), if installed, must be of an appropriate setting and located upstream
of the common neutral bonding point. Alternatively, the device must monitor the protective earth currents of the
system. Refer to the High Leakage Current Warning in the first part of this manual.
4. The outputs of all UPS Rack Systems must be connected to a common output bus.
5. The maximum recommended unbalance between the numbers of power modules in different racks is 3/5.
In order to comply to the above points even in a faulty condition, the following upgrade sequence is proposed.
30kW 60kW 90kW
120kW 150kW 180kW
240kW 270kW 300kW
330kW 360kW 390kW
420kW 450kW 480kW
Redundant
Fig.
5-2 Recommended upgrade sequence
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