Liebert Trinergy™ Cube Electrical INSTALLATION
Page 80 Installation Manual - 10H52243IM60 - rev. 7 - 06/2020
4.5. External protection devices in TN-C, TN-S, TT, IT systems
In the case of TN-C, TN-S, TT, and IT systems, the protection devices must be selected in accordance
with the applicable local and national regulations and standards.
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).
4.5.1. Use of differential protection devices
A differential device installed on the primary and bypass inputs supply senses the total earth leakage
current due to the presence of RFI filters on the UPS and the leakage on the loads connected to the UPS.
To avoid spurious operation, the following must be taken into consideration when selecting differential
protection devices for installation on input lines:
1) Nominal earth leakage value:
total UPS leakage current + load leakage current.
In nominal conditions the typical UPS earth leakage current exceeds 3A.
N.B. According to the product standard (see IEC/EN 62040-1), the maximum UPS earth leakage current
must not exceed 5% of the nominal input current.
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
Notice
In a neutral isolated system (IT) the installation of the UPS can modify the level of the impedance of the
system respect the ground, so it can interfere with existing insulation monitoring devices. It is
recommended to select adjustable devices in order to set the threshold values in accordance with the
actual impedance, taking in account the presence of the UPS.
Notice - Differential current breakers
- The UPS does not require differential protection devices to be connected upstream. 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 bypass 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 bypass Static Switch,
the isolated sources should be connected in parallel. A case-by-case analysis should be made
as to whether any resulting imbalance between the currents on the bypass lines is compatible
with the respective protection devices.
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