IB140012EN
For more information visit: www.eaton.com
Instructional Booklet
Effective: March 2021
Page
39
Operation and Maintenance Manual,
Automatic Transfer Switch Controller, ATC-900
-Immediately turn on Preferred Source Gen Start
-Start Emergency Source TDES counting down
Preferred
Available?
Emergency
TDES=0?
-Turn on Emergency Source Gen
Start
Yes
No
No
Emergency
Available?
-Set transfer switch to Preferred Source (No TDN or TDEN if
switch was previously on Emergency Source)
-Cancel Emergency Source TDES
-Set Emergency Source to Idle State
Yes
Preferred
Available?
-Set transfer switch to Preferred Source (No TDN or TDEN if
switch was previously on Emergency Source)
-Turn off Emergency Source Gen Start
-Set Emergency Source to Idle state
Yes
No
No
-Set transfer switch to Emergency Source (No TDN or TDNE if
switch was previously on Normal Source)
-No Change to Preferred Source Gen Start or state.
Yes
Secondary-In
Active?
-Turn off Preferred and Emergency Source Gen
Starts
-Set Preferred and Emergency Sources to Idle
state
-Follow normal procedures to transfer between
Primary and Emergency sources based on source
availability, etc.
Wait for next
Secondary-In Active
Secondary-In goes
Active
Yes
No
Secondary Controller with Preferred Source
During startup, if Emergency source comes up first, followed quickly by
Preferred source, the load will be initially powered by the Emergency
source followed by a transfer from Emergency to Preferred source with
normal TDEN/TDN delays. Use manual retransfer to avoid this if desired.
TDEC will be used to “cool down” Emergency generator.
