SL-21A Electric Switch Lock

Switch Machines and
Associated Equipment
Ansaldo STS USA
(Formerly known as Union Switch & Signal)
Rev. 7-03
SL-21A Electric Switch Lock
General Description
The SL-21A Electric Switch Lock prevents
unauthorized operation of hand throw levers on switch
stands. An electric control in the SL-21A provides the
only means of disengaging the lock. Basic
components include a magnet coil, armature, cam
operated contacts, locking dog assembly (with two
counterweights), and foot latch assembly. The
complete mechanism is housed in a low profile cast
iron case and uses a foot latch with a padlock for
added security.
In the normal position, the foot latch is pressed and
the padlock is in place. When the padlock is
removed, a coil return spring raises the foot latch,
applying voltage to the lock circuit and energizing an
armature. This results in lifting of the lock dog from its
notch and releasing the mechanism. The switch can
be thrown at this point. The spring-loaded foot latch
must be pressed to enable insertion of the padlock.
This action removes the voltage, causing the armature
to fail away and the lock dog to drop back into place,
thus securing the mechanism. Counterweights assist
the motion of the lock dog.
Normal arrangement of the cam operated contacts
are for the padlocked position. The back contacts are
closed and the front contact is open in this position.
Typically, there are one front and two back contacts,
while the armature normally has two back contacts
that are closed when the circuit is de-energized.
The SL-21A is for right-hand assembly. Other
optional items include lock rod and lock rod support.
ASTS USA can produce custom lock rods to customer
Ordering Information
Provides security for hand-throw switch levers
Positive-locking design, low profile
Easily installed and maintained
When ordering the SL-21A, please specify if wire
inlet plate assembly is to be installed on the hasp
or the hinge side.
Also specify type of switch stand that will
incorporate the lock.
Lever lock rod does not have a standard order
number. Order by dimensions shown in RSE-6H2.
Contact ASTS USA to order:
‐ Yale drawer lock
‐ Lock suitable for tandem application (locking
hand-throw lever in both normal and reverse
Refer to ordering tabulation on reverse side for SL21A top assembly part numbers and lock rod
support components.
Request ASTS USA Service Manual SM-3225 to
order SL-21A replacement parts.
See reverse side for unit and application dimensions.
To order, call 1-800-652-7276
RSE-6G1, p. 1
Ansaldo STS USA
SL-21A Electric Switch Lock
(Formerly known as Union Switch & Signal)
Rev. 7-03
Unit Dimensions
Order No.
Application Dimensions
SL-21A Locks
Mag. Coil Res.
Normal contact arrangement
With lubrication fittings
Lock Rod Support Components (all qty. = 1)
Order No.
RSE-6G1, p. 2
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