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No Preference Mode
Assume the Source I high-voltage switch (SW-I) is
closed and Source II high-voltage switch is open. With
the SOURCE PREFERENCE and RETURN MODE
switch (S4) in NO PREF-NP (Terminal 4 of S4 connect-
ed), loss of Source I voltage on one or more phases will
open the Source I high-voltage switch (SW-I) as
described in the Automatic Transfer, Preferred to
Alternate section of this discussion.
Upon restoration of Source I voltage, R2 is re-ener-
gized. However, due to the positioning of decks G and
H of S4, neither timer can be energized since both the
N.C. contacts 1-7 of R2, and 9-3 of R6 are open (both
relays are energized).
The S control is now in a quiescent state with SW-II
closed and SW-I open. This condition will continue until
either Source II is lost or a change is made in the control
settings. If Source II is lost, delay in transfer to Source I
will be timed by TM-2.
Preferred Source II Mode
With the SOURCE PREFERENCE and MODE switch
(S4) in either PREF II-P (Terminal 6 of S4 connected), or
PREF II-NP (Terminal 5 of S4 connected) the description
of operation is similar to the “Automatic Transfer,
Preferred to Alternate” and “Return Transfer, Parallel
Transition” or “Return Transfer, Non-Paralleled
Transition” as previously described except that Source II
is the preferred source (controlled by SW-II) and Source
I is the alternate source (controlled by SW-I).
Control Mode Switch, S5
If S5 is placed in the center-off TEST position, there is no
circuit to either the close or trip coils of either high-volt-
age transfer switch. This position of S5 is used to check
sensing circuitry, timers, and the latching relay without
affecting the status of the high-voltage switches.
If S5 is placed in the HOLD ON ALTERNATE position,
return transfer will not occur after preferred source volt-
age is restored. Assume the S3 is in AUTO, S4 is in
PREF l-P, and the S control is in the quiescent state with
Source I high voltage (SWI) closed and Source II high-
voltage switch (SW-II) open. Upon loss of Source I, R2
will again initiate a transfer of the latching relay R1 as
previously described, followed by the opening of SW-I
and the closing of SW-2. The S control is now in a qui-
escent state in which SW-2 will remain closed and SW-I
will remain open even when Source I power is restored.
When Source I is reenergized, R1 will transfer back to
the latch position and close its contact 9-6. However,
because deck L of S4 is open, power cannot be provided
to the trip coil of SW-II or the close coil of SW-I.
Manual Control
When the OPERATION SELECTOR switch (S3) is
placed in MANUAL, it connects the MANUAL OPER.
SOURCE I switch (S1) and the MANUAL OPER.
SOURCE II switch (S2) to the transfer bus. Power can
then be supplied to either the close or trip coils of either
SW-I or SW-II. Contacts 3-7 and 2-6 of S3 are opened in
the MANUAL position so that opening of one high-volt-
age transfer switch does not cause automatic closing of
the other. In the manual mode of operation, it is possible
to have both high-voltage switches open, either switch
closed, or both switches closed.
Indicating Lamps
The LAMP TEST switch (S6) is provided for checking the
various incandescent indicators on the front panel of the
S control. In the closed position, all the lamps will be
energized through a diode network to check their condi-
tion.
In the open position, the diode network isolates the
lamps from the test switch so that it has no effect on nor-
mal circuit operation.
S260-75-1
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SAFETY
FOR LIFE