External Protective Device; Power Cable Connection Steps - Liebert NXC 30kVA User Manual

Failure to ground as required can cause EMI, electric shock or fire risk.

3.1.9 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.
Rectifier and bypass input power supply
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 11-6 and Table 11-7) and the short circuit capability of the upstream power distribution. It is
generally recommended to use the thermomagnetic circuit breaker of IEC60947-2 tripping curve C (normal), when the
current value reaches 125% of the current value listed in Table 3-1.
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.
The rectifier input and bypass input must use the same neutral line.
3. Ground fault protection
If the pre-stage 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 0.3A ~ 3A adjustable
The RCCB symbols are shown in Figure 3-1.
The UPS has an internal EMC filter, therefore the protective earth cable has leakage current which is 0 ~ 1000mA. It is
recommended to confirm the RCD sensitivity of the upstream input distribution and the downstream distribution (to the
load).
External battery
The BCB is useful for protecting the external battery. The UPS provides an optional BCB box to provide overcurrent
protection, short circuit protection and automatic tripping functions for the external battery. The rated voltage of the
BCB is 500Vdc, and its DC breaking current is 20kA.
This BCB is important for the battery maintenance, and is generally installed near the battery.
System output
The UPS output distribution shall be configured with a protective device. The protective device shall be different from
the input distribution protection switch and able to provide overload protection (refer to Table 11-6 and Table 11-7).

3.1.10 Power Cable Connection Steps

For cable access mode of the UPS, refer to 2.6.3 Cable Access Mode.
Figure 3-1 RCCB symbols
Liebert NXC 30kVA And 40kVA UPS User Manual
Chapter 3 Electrical Installation
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