Cut Sheet

Volume 7—Logic Control, Operator Interface and Connectivity Solutions CA08100008E—July 2015 www.eaton.com V7-T3-191
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3.9
Control Relays and Timers
Alternating Relays
Typical Installations for DPDT Cross-Wired Alternating
Relays, Standard Installation
In the OFF state, both the LEAD control switch and the LAG
control switch are open, the alternating relay is in the LOAD A
position, and both loads are off. When the LEAD control switch
closes, it energizes the first load (M1). The red LED marked
“LOAD A” glows. As long as the LEAD control switch remains
closed, M1 remains energized. If the LAG control switch closes,
it energizes the second load (M2).
When the LAG control switch opens, the second load (M2) is
turned off. When the LEAD control switch opens, the first load
(M1) is turned off and the alternating relay toggles to the LOAD
B position.
Typical Installations for DPDT Cross-Wired Alternating
Relays, Anti-Bounce Installation
When the LEAD control switch closes, it turns on the second
load (M2). The red LED marked “LOAD B” glows. If the LAG
control switch closes, it will energize the first load (M1). When
the LAG control switch opens, the first load (M1) is turned off.
When the LEAD control switch opens, the second load (M2) is
turned off, the alternating relay toggles back to the LOAD A
position, and the process can be repeated again.
To eliminate any bounce condition of the control switch, the
addition of a second switch (OFF) along with two auxiliary
contacts is recommended as shown in the Anti-Bounce
Installation.
Typical Installations for DPDT Cross-Wired Relays for Three-Switch Applications
In the OFF state, all three switches are open, the alternating relay
is in the LOAD A position, and both loads are off. No action
happens with the alternating relay or either load when the STOP
switch closes. When the LEAD switch closes, Load #1 (M1) turns
on. When the LAG switch closes, Load #2 (M2) turns on. Both
loads remain on as long as all three switches are closed.
When the LAG switch opens, Load #2 (M2) remains on because
the STOP switch is still closed. When the LEAD switch opens,
Load #1 (M1) remains on because the STOP switch is still
closed. When the STOP switch opens, both Load #1 (M1) and
Load #2 (M2) are turned off simultaneously.
The alternating relay toggles to the LOAD B position. The entire
cycle is then repeated, but with Load #2 (M2) energized first
followed by Load #1 (M1). This type of operation is known as
“Sequence On–Simultaneously Off (S.O.S.O.)”—the two loads
are energized sequentially, but remain on together until the
STOP switch is opened.
If both the STOP switch and LEAD switch fail to close and turn
on the first load, both loads will be turned on simultaneously
when the LAG switch is closed.
L1
Lag
Lead
Cross-Wired
O/L
O/L
1
2
8
3
7
6
L2
M1
M2
Lag
Off
Lead
L2
L1
M1
Cross-Wired
M2
1
2
3
7
6
M1
M2
8
L1
Motor
1
Motor
2
L2
L3
L1
M1
M1
M1
M2
M2
M2
M2
M1
L2
L1
Lag
Switch
Lead
Switch
Stop
Switch
L2
L3
1
2
4
8
7
3
6
O/L
O/L