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Electrical Connections
11
2.0 ELECTRICAL CONNECTIONS
The UPS requires both power and control cabling once it has been mechanically installed. All control
cables must run separate from power cables in metal conduits or metal ducts that are electrically
bonded to the metalwork of the cabinets to which they are connected.
2.1 Power Cabling
2.1.1 Cable Rating
The main factors affecting the choice and size of cable are voltage, current (also taking into account
overcurrent), room temperature and conditions of installation of the cable.
The power cables of the system must be sized with respect to the following description:
• UPS input cables - The UPS input cables must be sized for the maximum input current, includ-
ing the maximum battery recharge current, given in Table 8, with respect to the unit rating and
the input AC voltage.
• UPS bypass and output cables - The bypass and output cables must be sized for the nominal
output current, given in Table 8, with respect to the unit rating and the output AC voltage.
• Battery cables - When connecting an external battery cabinet, the battery cables must be sized
for the battery discharge current at the end-of-discharge voltage, as given in Table 8, with
respect to the unit rating.
The power cables can be sized to suit the UPS unit rating according to Table 8.
Lug Size and Torque Requirements
Refer to Table 24 for lug size and torque requirements.
!
WARNING
Before connecting input power to the Liebert NX, ensure that you are aware of the location
and operation of the overcurrent protection devices that connect the UPS input/bypass supply
to the power distribution panel.
De-energize and lockout or tagout all incoming high- and low-voltage power circuits before
installing cables or making any electrical connections.
NOTE
Table 8 gives nominal currents for determining the size of UPS power cables. Other important
factors to consider include cable route length and coordination with protective devices.
NOTE
When installing a Liebert NX with Softscale
™
capability Liebert recommends sizing the input,
bypass and output cabling for the UPS’s maximum rating. Properly sizing the cable will
reduce the work required to upgrade the UPS.