Electrical Connections—UPS
Liebert
®
eXM
™
16
Torque Requirements
Refer to Tables 3 and 4 for lug size and torque requirements.
3.2 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 be knowledgeable about regulatory
wiring standards and the equipment to be installed.
To reduce the risk of fire, connect only to a circuit provided with branch circuit overcurrent protection
in accordance with NEC ANSI/NFPA 70.
3.2.1 Rectifier and Bypass Input Supply of the UPS
Overcurrents
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. Generally, the
magnetic circuit breaker with IEC60947-2 tripping curve C (normal) at the 125% of the nominal
current listed in Table 23 is recommended.
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. A shunt trip coil of 120V
must be installed in the bypass input breaker if the system does not include a Liebert Bypass
Cabinet.
Earth Leakage, RCD Devices
Any residual current detector (RCD) installed upstream of the UPS input supply:
• Must be sensitive to DC unidirectional pulses (Class A)
• Must be insensitive to transient current pulses, and
• Must have an average sensitivity, adjustable between 0.3 and 1A.
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.
3.2.2 UPS Output
If an external distribution panel is used for load distribution, the selection of protective devices must
provide discrimination with those that are used at the input to the UPS (see Table 28).
Table 3 Busbars—Power wiring
Bolt Shaft Size Lb-in (Nm)
1/2" (M12) 428 (48)
Table 4 Terminal block with compression lugs—Control wiring
AWG Wire Size
or Range Lb-in (Nm)
#22 - #14
3.5 to 5.3
(0.4 to 0.6)
NOTE
The rectifier input and bypass input must use the same neutral line.
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