Source 1 is available
Is Source 2
available?
Close Source 2 contactor
(Momentarily energize K4)
N
Dual Utility Transfer Switch
Close Source 1 contactor
(Momentarily energize K3)
Source 1 becomes unavailable
(or Go To Emergency)
TDNE timer times out
Open Source 1 contactor
(Energize K2)
Y
Source 2 is powering the load
Close Source 1 contactor
(Momentarily energize K3)
Source 1 is powering the load
TDN timer times out
(if Option 32A is enabled)
TDN timer times out
(if Option 32A is enabled)
Source 1 is powering the load
N
Is Source 1
available yet?
TDEN timer times out
Y
Open Source 2 contactor
(Energize K1)
Send Pretransfer signal. TPRE times out.
(if Pretransfer enabled)
Send Pretransfer signal. TPRE times out.
(if Pretransfer enabled)
IB140036EN
For more information visit: www.eaton.com
Instruction Booklet
Effective: October 2014
Page
31
O&M Manual for 40-1200A (480/600 Vac) ATC-900 3-Position,
Open/Closed Transition Contactor Based Transfer Switch
Figure 21. Dual Utility Transfer Switch.