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Remote EPO (Emergency Power Off)
Some applications (notably, data centers) require that there is a provision to remotely shut
down power to the equipment powered by the UPS. Typically, this "remote" control is a red
button switch located next to the exit and wired to the UPS. However, shutting down the
UPS will have no effect on power to the load if the load is being powered by the Bypass
Breaker in the MBS. The Parallel Output Redundant Cabinet with MBS arrangement is
equipped with a Remote EPO input that causes both the Bypass Breaker (Breaker #2) and
both UPS Output Breakers (Breaker #3 and Breaker #5) to trip when a switch activation is
sensed. This way, power to the load is interrupted regardless of which breaker was
actually supplying current to the load. Note that the use of the REPO feature is optional
unless required by local codes.
Each UPS is also equipped with a REPO input, but this is completely independent of the
REPO system that is part of the MBS arrangement in this transformer cabinet. If it is
desired to have the same switch activate both the MBS REPO and the UPS REPO, a
switch with three sets of contacts needs to be used. One set of contacts would wire to this
cabinet as described in Section 4 and the other sets would wire to each of the UPS per the
instructions in the UPS manual. The UPS switch must be “normally closed”.
Some users prefer to use a normally open switch in the REPO system; others prefer a
normally closed switch. Inputs for both types of switches are provided in the Parallel
Output Redundant Cabinet with MBS arrangement, but the normally closed function has to
be enabled by operating a small rocker switch on the Options Control Board. This is to
avoid the problem of not being able to operate the system if the normally closed circuit is
missing, as when the user only chooses to use the normally open configuration, or when
the user does not choose to use the REPO system at all.
Historically, REPO systems have caused a lot of confusion due to systems being inhibited
from operation due to a defective REPO switch circuit that causes the REPO to remain
active (examples: latched switch mechanisms, shorted wiring, open wiring). To help identify
this condition, the Options Control Board has a yellow LED lamp (DS1 in the upper right
corner of
Figure 4
) that indicates that the REPO has been activated. The logic that
operates the lamp latches the indication, so it is possible to determine that the REPO was
activated at some time since power was applied to the system. The latched indication can
be reset by pressing S1 on the Options Control Board. If pressing S1 fails to extinguish
DS1, then the REPO switch circuit is still active.
