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14 Configuring Your Neutral and Ground Connections
7.0 CONFIGURING YOUR NEUTRAL AND GROUND 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 straight
delta or corner-grounded delta, contact your Liebert representative for details of the Artificial
Neutral or Isolated Neutral kits for the System Control Cabinet.
• What are the UPS input and output voltages? Systems with 480 VAC input and output have
significantly different needs than systems with 208/208 VAC.
• 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.