I.B. 48006
Page 4
Effective 11/97
OPERATION
Figure 3 shows a latch assembly before it is mounted on
a contactor. The enlarged detail shown in Figure 4 shows
the relationship between the cam roller on the end of the
latch arm and a notch in the lower left corner of the
contactor armature. When the latch is installed, it
appears as shown in the lower portion of Figure 4.
Latch sensitivity can be understood by studying the inset
of Figure 4, which is a magnified detail view showing the
lower left corner of the armature and the cam roller. The
cam roller travels between positions (U) and (L) through
an arc around the latch shaft. In the unlatched (open)
contactor position, the cam roller is in position (U). It
cannot travel upward to position (L) even though the latch
spring is pushing the latch arm upward because latch
edge (F) of the armature stops it. However, when the
contactor operating coil is energized, the armature
rotates toward the magnet and latch edge (F) travels
across the cam roller easily. As latch edge (E) passes
the centerline of the cam roller, the roller starts moving
upward, driven by the latch spring. By the time the
armature reaches the magnet, the cam roller passes
completely by latch edge (E) into position (L), and the
contactor is latched closed.
The cam roller cannot travel to the top of the notch in the
armature because the latch arm stops against the latch
adjustment bolt. The further into the notch the cam roller
penetrates, the less sensitive the latch becomes.
There will always be some “free-play” clearance between
the contactor armature and magnet in order to provide
free motion. This clearance needs to be only a few
thousandths of an inch; so for practical purposes, the
contactor is held “fully” closed.
When either or both trip solenoids are momentarily
energized, their armatures push the latch arm downward
against its spring. As the centerline of the cam roller
passes below latch edge (E) of the armature, the
contactor armature will snap to the fully open position;
i.e., the contacts are open.
Fig. 3 Mechanical Latch Assembly
5259C56
