7
Configuration and Operation
Automatic Transfer Switch
When the Primary and Secondary inputs are both connected to Tripp Lite UPS Systems, the PDU
operates as an Automatic Transfer Switch, providing redundant input power for high availability
applications. Under normal operating conditions, the PDU will distribute power from the Primary
input source, switching to the Secondary input source under certain conditions. The PDU will switch
to the Primary source whenever it is Good according to the PDU input voltage definitions (see below).
Preferred Configuration
The Automatic Transfer Switch function
provides increased availability when the
Primary and Secondary inputs of the PDU are
connected to separate Tripp Lite UPS Systems
that are connected to separate utility power
sources. For maximum availability, Tripp Lite
recommends using matching SmartOnline™
UPS Systems with pure sine wave output for
the Primary and Secondary input power
sources. The automatic transfer switch function
will be compromised if the primary and
secondary inputs are connected to the same
utility power source.
Facility Circuit
Facility Circuit
PDUMH15AT
Critical Equipment
Loads
Secondary UPS
Primary UPS
Primary Input Cord
Secondary Input Cord
Utility B
Utility A
Automatic Transfer Switch Source Selection
Upon power-up, the PDU looks for a source >85V. If it is unable to find a source >85V, it remains off.
Input voltage definitions:
99V < V
in
< 139V Good
75V < V
in
< 99V Fair
V
in
< 75V Bad
In normal operation (after power-up), if the selected source is no longer Good, the PDU will attempt
to switch to the other source, but only if the other source is Good. If the selected source becomes Fair
and the other source is not Good, the PDU will keep the loads connected to the selected source until
the selected source becomes Bad, at which point the loads will be disconnected (note that the source
selection doesn't change). After the loads are disconnected, they remain disconnected until the
selected source becomes >85V, or until the other source becomes Good.
200706235 93-2702 PDUMH15-20AT OM.qxd 7/11/2007 4:40 PM Page 7
