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Single Module UPS Installation
7
Earth Leakage (RCD):
Any residual current detector (RCD) installed upstream of the UPS input supply must be:
• sensitive to DC unidirectional pulses (Class A)
• insensitive to transient current pulses, and
• must have an average sensitivity, adjustable between 0.3 and 1A.
Figure 1 Residual current circuit breakers (RCCB) symbols
To avoid false alarms, earth leakage monitoring devices when used in systems with split-bypass input
or when used in paralleled UPS configurations, must be located upstream of the common neutral
sinking point. Alternatively, the device must monitor the combined four-wire rectifier and split-
bypass input currents.
The residual earth current introduced by the RFI suppression filter inside the UPS is greater than
3.5mA and less than 860mA. Liebert recommends verifying the selectivity with all other differential
devices both upstream of the input distribution board and downstream (toward the load).
1.5.2 External Battery
The UPS and its associated batteries are protected against overcurrents through a DC compatible dis-
connect device.
1.5.3 UPS Output
Any external distribution board used for load distribution shall be fitted with protective devices that
discriminate with those used at the bypass input to the UPS and with the UPS overload characteris-
tics (see Table 35).