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12 InfraStruXure System—Installation and Start-Up
Cross Tie Output Circuit Breaker
Overview
The optional cross tie output circuit breaker allows two separate UPSs that are fed from two different
power sources (dual-fed) to be tied together to create a 2N system. The illustration below shows an
example configuration.
With a dual-fed 2N system, the secondary of UPS A’s input transformer, located within PDU A, is
connected to the bypass feed of UPS B; and the secondary of UPS B’s input transformer, located
within PDU B, is connected to the bypass feed of UPS A.
The purpose of a 2N system is to use two UPSs such that if something were to happen to one of the
UPSs, the other UPS is available to supply power to the load equipment. 2N systems provide an
added benefit for 480V and 600V power distribution systems in that isolation transformers are not
required to step down the 480V or 600V input to 208V because transformers in the PDUs perform
this task.
It is important to note that the cross tie feature is to be used on 2N dual-fed systems only. The cross
tie circuit breaker is not to be used to supply power to any other load device. Cross tie connections are
made through the load-side terminals of a molded-case circuit breaker, located in the front, upper,
right-hand side of the PDU. PDUs with the bottom feed option are supplied with terminals on the
front, lower, right-hand side of the PDU.
AABBXX
PDU A PDU B
POWER SOURCE A
POWER SOURCE B
To UPS To UPS
Input
Step-down
Transformer
Input
Step-down
Transformer