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Operating Instructions
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4.2.6 Returning an Isolated System to Normal Operation - End Combined Loads Operation
One Load circuit breaker and the Tie circuit breaker are closed. The Load circuit breaker of the iso-
lated system which was being serviced will be opened.
1. Select the UPS system to accept the load. Press the TRANSFER LOAD TO SYSTEM (#). If
System 2 had been isolated then press the SYSTEM 2 button. Load 2 will be returned to System 2.
2. Wait for the OK TO TRANSFER LOAD light to turn on. If System 2 was isolated then the OK TO
TRANSFER LOAD 2 TO SYSTEM 2 light should turn on when it is safe to perform the transfer.
3. After the OK TO TRANSFER LOAD 2 TO SYSTEM 2 light turns on, press the PUSH TO
TRANSFER AFTER OK button. The transfer will be performed. If System 2 was isolated then the
Load 2 breaker will close and the Tie circuit breaker opens after the overlap period times out.
4. Both UPS systems will now be supplying their normal Load and operating independent of each
other.
4.2.7 Maintenance Procedures - Maintaining Power-Tie Components
Refer to the procedures in 4.2.3 - Maintenance Procedures - Isolating Each UPS System to iso-
late the UPS’s load circuit breaker and the associated downstream feeders for service.
By using downstream switchover devices for the individual critical loads, such as ATSs or dual input
PDUs, the load feeder components to be maintained are de-energized. All critical load operations are
transferred to the feeder which will power the combined loads.
There are three approaches to maintaining the Tie circuit breaker and its associated circuit compo-
nents depending on the convenience and isolation desired.
1. Single fixed-mount Tie circuit breaker
Complete UPS system and critical loads must be placed on a reliable maintenance bypass source
(e.g., standby engine-generator) to de-energize the Tie circuit breaker.
Using appropriate safety equipment and procedures, the Tie circuit breaker can be serviced while
one or both systems remain energized (depending on isolation breaker usage).
2. Single drawout Tie circuit breaker
Drawout mechanism permits servicing the Tie circuit breaker and associated circuitry while the
Power-Tie system is in its normal mode of operation.
To de-energize the drawout carriage plug-in stubs and buswork, however, one feeder at a time
must be isolated for service. Refer to 4.2.3 - Maintenance Procedures - Isolating Each UPS
System.
Using appropriate safety equipment and procedures, these components can be serviced while one
or both systems remain energized (depending on isolation breaker usage).
3. Two Tie circuit breakers in series—Fixed-mount or Drawout
By using two Tie circuit breakers in series, each circuit breaker and its associated buswork can be
conveniently and completely de-energized for service. Refer to 4.2.3 - Maintenance Procedures
- Isolating Each UPS System.
Using appropriate safety equipment and procedures, these components can be serviced while one
of the two systems remains energized.
4.2.8 Maintenance Procedures - Tie Control Logic Components
Unless the controls are in a continuous parallel mode or currently in the process of transferring a
load, it is possible to service the Tie controls by taking a few precautions. Since all control signals are
isolated, they can be safely de-energized for maintenance without affecting the UPS systems.