MaxPower Corp Gamatronic Power+ M50-RM - Manual (Page 48)

Gamatronic Electronic Industries Ltd.
POWER+ RM 50 K VA, N.Am. Std. – User Guide, Release 1.9 32
5.2 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.
5.2.1 A 4-pole switch might disconnect the neutral line
WARNING! If you have a mains-to-generator four-pole switching system, the UPS's neutral
line may become 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 25 on page 33 illustrates the wrong way to connect the UPS with a grounded-neutral
generator.
Figure 26 on page 34 illustrates an acceptable connection solution if you already have a
grounded-neutral generator.
Figure 27 on page 35 shows the preferred generator (neutralized, not grounded) and the
preferred connection (three-pole).