14 Configuring YourNeutral and Ground Connections
7.0 CONFIGURING YOUR NEUTRAL AND GROUND CONNECTIONSImproper grounding is the largest single cause of U PS installation and start-up problems. This is
not an easy subject, since grounding techniques vary significantly from site to site, depe nding on
several factors. The question s you should ask are:
• What is the configuration of the input power source?Most of the recommended schemesfor
UPS grounding require g rounded-wye service. The UPS syste m requires a bypass neutral for
sensing and monitoring the quality of the by pass input. If the building service is straight
delta or corner-groundeddelta, contact your Liebert representative for details of the Artificial
Neutral or Isolated Neutral kits for the System Control Cabinet.
• W hat are the UPS input and output voltages? Systems with 480 VAC input an do utput 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 isolationtransformers?
The following sections discuss recom mended grounding procedures for various sys tem configura-
tions.
NOTE
Some UPS modules are equipped with inputis olationtransformers.
However,these transformers have no effectupon any system grounding
considerations. These modules will be grounded exactlyas shown in the
following examples.