Vertiv Liebert APM2 - Page 44

Install suitable protective devices in the distribution line of the incoming mains supply, considering the power
cable current carrying capacity, system overload capacity (see Table 12.6 on page173 and Table 12.7 on
page174) and the short circuit capability of the upstream power distribution. The protective devices should
provide functions such as the overcurrent protection, short circuit protection, isolation protection and tripping
upon backfeed.
2. Split bypass configuration
If the UPS uses split bypass configuration, a separate protective device should be installed respectively on the
rectifier input and bypass input in the distribution lines.
NOTE: The rectifier input and bypass input must use the same neutral line.
NOTE: For IT grid system, 4-pole protective components must be installed for the UPS external input power
distribution.
NOTE: Users need to pay attention to the selection of UPS external upper and lower-level power distribution switches,
and ensure that the UPS external upper and lower level power distribution circuit breakers meet the selective
protection requirements.
3. Ground fault protection
If the upstream input power supply has a residual current detector (RCD), the transient state and steady state
ground leakage current upon the startup of the UPS must be considered.
The residual current circuit breakers (RCCB) must meet the following requirements:
• Must be sensitive to the DC unidirectional pulse (class A) of the whole distribution network.
• Must be insensitive to transient state current pulse.
• Must have an average sensitivity, adjustable between 0.3 A to 3 A.
The RCCB symbols are shown in Figure 4.1 below.
Figure 4.1 RCCB Symbols
The UPS consist of an internal EMC filter, therefore the protective earth cable’s leakage current is less than 3000 mA. It is
recommended to verify the RCD sensitivity of the upstream input distribution and the downstream distribution (to the load).
36 Proprietary and Confidential ©2023 Vertiv Group Corp. 4 Electrical Installation
Vertiv™ Liebert® APM2 30 to 120 kVA Modular UPS User Manual