Type B Vital Relays - Alstom

Theory of Operation
2.5.4. Switch-Overload Relay
The Type B1 switch-overload relay picks up on motor overload current through its lowresistance
coil, and sticks up on control circuit energy through its high-resistance coil.
See Figure 2–30 for an example of relay wiring.
(FRONT VIEW)
26
25
24
23
22
21
I
O
I
O
3A
3B
3C
3D
(–)
(+)
(+)
(–)
HOLD COIL
PICK COIL
THICK WIRING IS PLUGBOARD WIRING.
THIN WIRING IS RELAY WIRING.
I = "IN" LEAD
O = "OUT" LEAD
Figure 2–30. Switch-Overload Relay Wiring
Pickup of the relay releases the switch control relays, thus removing energy from the
switch machine motor. When the polarity is reversed, the stick circuit opens and the
overload relay releases, permitting reversal of the switch movement.
Built-in thermal slow pickup characteristics prevent the relay from operating on normal
starting surges of the switch motor. This feature also permits repeated switch operation
that may dislodge the switch obstruction that is causing the overload.
Switch-overload relays are available for low- or high-voltage switch machines.
P1457, Rev. Nov/07 2–33 Alstom Signaling Inc.