MaxPower Corp Gamatronic Power+ M50 - Manuel (Page 38)

Gamatronic Electronic Industries Ltd.
22 POWER+ 3x208 V, User Guide, Release 2.3
4.3 The Power+ always requires a neutral line
During both installation and operation of the Power +, a neutral line must always be connected
to the UPS. This neutral line shall be connected during the entire period that the UPS is
working, and shall 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. That may result in system defining its own reference voltage, which will be set
by the load distribution between the three phases. This can result in serious damage to the
UPS.
4.3.1 A 4-pole switch might disconnect the neutral line
WARNING! If you have a mains-to-generator four-pole switching system, you are in danger
of having the neutral line disconnected when the four-pole switch is operated. This can result
in the problems 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 will constantly provide the
UPS with a neutral line.
Figure 22 on page 23 illustrates the wrong way to connect the UPS with a grounded-neutral
generator.
Figure 23 on page 24 illustrates an acceptable connection solution if you already have a
grounded-neutral generator.
Figure 24 on page 25 shows the preferred generator (neutralized, not grounded) and the
preferred connection (three-pole).