Chapter 1 Installation Of UPS Rack System 12
1.5 External Protective Devices
For safety concerns, it is necessary to install external circuit breakers or other protective devices for the input AC
supply of the UPS system. This section provides generic practical information for qualified installation engineers. The
installation engineers should have the knowledge of the regulatory wiring standards, and of the equipment to be
installed.
1.5.1 Rectifier And Bypass Input Supply Of The UPS
Over currents
Install suitable protective devices in the distribution unit of the incoming mains supply, considering the power cable
current-carrying capacity and overload capacity of the system (see Tab.
9-7).
Generally it is recommended a magnetic circuit breaker with IEC60947-2 tripping curve C (normal) rated at the 125%
of the current listed in Tab.
9-7.
Split bypass: In case a split bypass is used, separate protective devices should be installed for the rectifier input and
bypass input in the incoming mains distribution panel.
Note
The rectifier input and bypass input must use the same neutral line.
Note
For IT power network system, 4-pole protective device must be installed on the external input distribution and external output
distribution of the UPS.
Protection against earth faults (RCD devices):
The RCD device installed upstream of the input supply should be:
Sensitive to DC unidirectional pulses (class A) in the network
Insensitive to transient current pulses
Have an average sensitivity that is adjustable between 0.3A and 1A.
Fig.
1-3: The symbols of RCCB
When using the RCD in the split bypass system or parallel system, the RCD should be installed in the upstream of
the input distribution to avoid wrong alarm.
The residual current introduced by RFI filter in the UPS is between 3.5mA and 1000mA. It is recommended to confirm
the sensitivity of each RCD of upstream input distribution and downstream distribution (to load).
1.5.2 External Battery
The DC compatible circuit breaker provides over current protection for UPS system and battery, which is provided by
the external battery cabinet. See Appendix A for a selection guide
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