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Power+ PREMIUM, Installation Guide, rel.
1.7
3.2
Cabling
3.2.1
Neutral line
During both installation and operation of the Power+ Premium,
a neutral line must always be connected
to the UPS
. This neutral line must be connected at all times while the UPS is working and should not be
disconnected at any time.
CAUTION!
If at any time the neutral line becomes disconnected, there will be no input
or output reference voltage because the input neutral line and the output neutral line
are physically linked together. This may result in the system defining its own reference
voltage, which will be set by the load distribution between the three phases.
This can
cause serious damage to the UPS.
CAUTION!
If you have a
four-pole
mains-to-generator
switching system you are in
danger of having the
neutral line disconnected
when the four-pole switch is operated.
This can result in the problem described above.
To avoid these problems, we strongly recommend that, if you use a four-pole mains-to-
generator switching system, you install an isolation transformer that constantly provides
a neutral line to the UPS.
Figure 28 shows the wrong way to connect the UPS with a grounded-neutral generator.
Figure 29 shows an acceptable connection solution if you already have a grounded-neutral generator.
Figure 30 shows the preferred generator (neutralized rather than grounded) and the preferred connection
(three-pole).
Figure 28: Wrong way to connect Power+ with a four-pole switch
