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12 Configuring Your Ground and Neutral Connections
7.0 CONFIGURING YOUR GROUND AND NEUTRAL CONNECTIONS
Improper grounding is the largest single cause of UPS installation and start-up problems. This is
not an easy subject, since grounding techniques vary significantly from site to site, depending on
several factors. The questions you should ask are:
• What is the configuration of the input power source? Most of the recommended schemes for
UPS grounding require grounded-wye service. The UPS system requires a bypass neutral for
sensing and monitoring the quality of the bypass input. If the building service is ungrounded
delta or corner-grounded delta, contact your Liebert representative to ensure your system
• What is the configuration of the UPS equipment? A Power-Tie system has different needs
than a standalone UPS module.
• What is the connected load? Does the critical load consist of one or more Power Distribution
Units (PDUs)? Do the PDUs have isolation transformers?
The following sections discuss recommended grounding procedures for various system configura-
tions.
NOTE
Some 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 the
following examples.