User Manual 10H52188UM60 - Rev. 2 - 09/2012 23
Liebert NXC Single UPS Installation And Commissioning
Figure 3-2 External protective device for backfeed protection
Earth leakage current
The residual current detector (RCD) for the UPS upstream input power distribution should be:
Sensitive to the DC unidirectional pulse (level A) in power distribution network
Insensitive to the transient current pulse
The residual current circuit breaker (RCCB) must be sensitive to the DC unidirectional pulse (level A) in power distribution
network, but insensitive to the transient current pulse, as shown in Figure 3-3 respectively.
Figure 3-3 RCCB symbols
When using the earth RCD in split-bypass system or parallel system, the RCD should be installed at the upstream input power
distribution terminal to avoid generating false alarms.
The earth leakage current introduced by the RFI filter in the UPS ranges from 3.5mA to 1000mA. It is recommended to
confirm the sensitivity of each differential device of the upstream input power distribution and downstream power
distribution (to load).
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