22 User Manual 10H52188UM60 - Rev. 2 - 09/2012
Single UPS Installation And Commissioning Liebert NXC
3.3 External protection devices
This device is equipped with manual switches intended only for Service Bypass and Internal Service operations. It is therefore
essential that the customer install external protection devices at the installation site. These must be installed near the unit and
labeled as the line power separation device for the UPS (see IEC/EN 62040-1).
Warning
The following label must be displayed on all switching devices installed in the same electrical system as the UPS, even when they are
located far from the area where the system is located (according to European standard IEC/EN 62040-1):
MAKE SURE THE UNINTERRUPTIBLE POWER SYSTEM IS ISOLATED
BEFORE WORKING ON THIS CIRCUIT
Use of differential protection devices
Note: Differential Current Breakers
The UPS does not require differential protection devices connected ahead of it. However, when these devices are installed in compliance
with local regulations, note that separate DCBs in the line power and bypass line power circuits may trip unexpectedly, thus interrupting
the power supply to the unit. Therefore, if a DCB must be installed, only one should be used for both primary and bypass inputs.
In parallel distributed systems, only one common differential protection device should be installed ahead of the point where the line
divides into the UPS primary and bypass line power circuits. If separate DCBs are installed in different configurations, they may trip
unexpectedly.
In order to guarantee correct distribution in the neutral cables, installation personnel shall make sure that the lengths of the cables are
as equal as possible. However, if the bypass lines lead from sources that are electrically isolated from each other, a differential
protection device may be installed on each line. In this case, and in cases when the load is supplied from the Bypass via the Static Bypass
Switch, the isolated sources are connected in parallel. A case-bycase analysis should be made as to whether any resulting imbalance
between the currents on the Bypass lines is compatible with the respective protection devices.
3.3.1 Rectifier And Bypass Input
Overcurrent
The appropriate overcurrent protective device should be installed at the mains input power distribution, and the current
capacity of power cable and the system overload requirements should be taken into account in installation. It is recommended
to use the thermo magnetic circuit breaker which satisfies with IEC/EN 60947-2 tripping curve C (normal) when the current
value reaches 125% of the current value listed in Table 3-1.
Split-bypass
When the system adopts split-bypass, separate protective devices should be installed at the mains input power distribution
respectively for the mains and bypass.
Bypass backfeed protection
When using the bypass backfeed protection function, it is necessary to install a protective device with auxiliary contact
function upstream of the UPS bypass input; the auxiliary contact should be connected to the system opto-coupled contact
port (refer to section 7.2 and Figure 3-2).
Note
The same neutral line must be used for the rectifier and bypass power.
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