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Chapter 12 Helpful information
UPS units and emergency power systems
UPS units
UPS units are devices which charge up their batteries during normal supply of power by the
utility provider and supply the protected load with electricity in case the utility power fails. The
most common UPS design and operation modes are off-line, line-interactive and on-line
double conversion.
For UPS systems supplied with three-phase current (delta connection), L1, L2, L3 and PE are
being used. In such a set up the N is usually not required. The PE is rigidly connected from
input to output.
With three-phase alternating current (Y connection) L1, L2, L3, N and PE are available. In this
set up N and PE of the input are permanently connected to N and PE of the output. The single-
phase design of the UPS unit must be connected accordingly.
The N of the input must be rigidly connected to the N of the output, otherwise it will lead to
the floating of N (Y point shift) which will lead to massive disturbances of the fed electronic
devices. N and PE must
UPS units without a bypass circuit can be built using isolated transformers. In this case only
the PE is to be connected. Such a UPS unit is to be considered a TN-S earthing system and is
NOT TO BE CONNECTED
the equipment. As an example the UPS unit should
distribution box for protecting any load. According to the rules applicable to TN-S earthing
system N and PE are to be bridged in these UPS units.
6U Rack or Tower UPS RT8kVA and RT11kVA IUOMG
NOT BE BRIDGED
the normal power supply provided by the utility provider in front of
in the UPS!
NOT BYPASS
a local, dedicated, power
201
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