UPS Electrical Installation
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2.6 Configuring Neutral and Ground Connections
Improper grounding is the largest single cause of UPS installation and startup problems. Grounding
techniques vary significantly from site to site, depending on several factors.
Proper grounding should be based on the appropriate NEC sections, but safe and proper equipment
operation requires further enhancements. The following pages detail recommendations for grounding
various system configurations to ensure optimal UPS system performance.
2.6.1 Four-Wire Input connections
The UPS module bypass input is connected to a solidly grounded source. In this configuration, the
UPS module is not considered a separately derived source. The UPS module output neutral is solidly
connected to the bypass source neutral, which is bonded to the grounding conductor at the source
equipment.
Figure 10 Grounding diagram—Four-wire single-module systems
NOTE
These UPS modules are equipped with input isolation transformers. However, these
transformers have no effect upon any system grounding considerations. These modules will be
grounded exactly as shown in Figures 10 through 13.
CAUTION
The UPS ground lug must be solidly connected to the service entrance ground by an
appropriately sized wire conductor per the NEC. Each conduit or raceway containing phase
conductors must also contain a ground wire, both for UPS input and output, which are solidly
connected to the ground terminal at each termination point. Conduit-based grounding
systems tend to degrade over time. Therefore, using conduit as a grounding conductor for UPS
applications may degrade UPS performance and cause improper UPS operation.
UPS
Source
G
N
BPSS
N
G
To connect equipment
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