4.1.9 External Protective Device
To ensure the safety, it is necessary to install external circuit breaker for the input and battery of the UPS. Because of the
difference of the specific installations, this section only provides general practical information for the installation engineer.
The qualified installation engineer should have the knowledge of the local wiring regulations on the equipment to be installed.
Input power supply of rectifier and bypass
1. Input overcurrent and short circuit protection
Install suitable protective devices in the distribution line of the incoming mains supply. The protective devices
should provide functions such as the overcurrent protection, short circuit protection, isolation protection, and
tripping upon backfeed. When selecting the protective devices, consider the power cable current-carrying
capacity, system overload capacity (see Table 12.6 on page175) and (see Table 12.7 on page176) and the short
circuit capability of the upstream power distribution.
2. Split bypass configuration
If the UPS adopts split bypass configuration, independent protective device shall be installed respectively on the
rectifier input and bypass input distribution lines.
N O T E: The rectifier input and bypass input m ust use the sam e neutral line.
N O T E: For IT grid system , 4 -p ole protective com ponents m ust be installed for the U P S external input
pow er distribution.
3. Ground fault protection
If the upstream input power supply has an RCD, the transient state and steady state ground leakage current
upon the startup of the UPS shall be considered.
The RCCB shall meet the following requirements:
• Be sensitive to the DC unidirectional pulse (class A) of the whole distribution network
• Be insensitive to transient state current pulse
• Have an average sensitivity which is 0.3 A to 3 A adjustable
The RCCB symbols are shown in Figure 4.1 below.
Figure 4.1 RC C B sym bols
The UPS has an internal EMC filter, therefore the protective earth cable has leakage current which is less than
3000 mA. It is recommended to confirm the RCD sensitivity of the upstream input distribution and the
downstream distribution (to the load).
External battery
4 Electrical Installation
31
Vertiv™ Liebert® APM Plus User Manual
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