Single Module UPS Installation
7
1.5.1
Rectifier and Bypass Input
Overcurrent protection must be installed at the distribution panel of the incoming main supply. The
protection must discriminate with the power cables current capacity and with the overload capacity of
the system (see
Table 38
). As a guideline, a thermomagnetic circuit breaker, with an IEC 60947-2
trip curve C (normal) for 125% of the current listed in
Table 1
is suitable.
Split-Bypass
—If a split-bypass is used, install separate protective devices for the rectifier and for
the bypass in the incoming mains distribution panel.
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, 1000mA for 30-80kVA, 2000mA for 100-120kVA models and less than 2500mA for
140-200kVA models. 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 38
).
NOTE
Rectifier and bypass input sources must be referenced to the same neutral potential.
NOTE
For IT power systems, four-pole protective devices must be used, external to the UPS, both
upstream of the input distribution panel and downstream (toward the load).
