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Configuring Your Neutral and Ground Connections
17
6.5 Grounding Configuration, Corner-Grounded Delta or Impedance-Grounded Wye
As previously mentioned, Series 610 UPS modules require a bypass input neutral for sensing and
monitoring. With a wye-connected input source, the installer should always connect the building ser-
vice neutral to the module output neutral to achieve this. When the building service is delta-con-
nected, however, the installer must take special steps to ensure reliable UPS functioning.
If the building service is corner-grounded delta or impedance-grounded wye, the UPS requires the
Series 610 Isolated Neutral Kit. This kit uses control isolation transformers to create a reference
point. For this application, the UPS output neutral must not be bonded to the UPS ground.
Figure 5 Grounding configuration, corner-grounded delta
Figure 6 Grounding configuration, impedance-grounded wye
These configurations have the same restrictions as explained in 6.2 - Alternate Grounding Config-
uration, Wye-Connected Service, except for the wye input. The UPS input and bypass must be fed
from the same source. The load must be strictly 3-wire. And the GFI time delay should be set to at
least 0.2 seconds to prevent tripping during transfer or retransfer operations.
!
CAUTION
Failure to properly set the ground fault interrupters could cause loss of power to the critical
load.
GROUNDING
ELECTRODE
PER NEC 250-24
LOCAL
GROUNDING
ELECTRODE
PER NE
C
250-3
0
GROUNDING
ELECTRODE
PER NEC 250-24