Instruction Bulletin
Instructions for Installation,
Page 4
Effective: July 2016
Operation and Maintenance of the
SL800 Classic 7.2 Kilovolt, 720 Amp. Vacuum Contactor
For more information visit:
www.eaton.com
IB48082
The moving contacts are driven by a molded plastic
crossbar rotating with a square steel shaft supported
by two shielded, pre-lubricated ball bearings that are
clamped in true alignment for long life and free
motion. Only the end edges of the square shaft are
rounded to fit the bearings, so that portions of the
four shaft flats go through the bearings for positive
indexing of the mechanical safety interlocks.
The contacts in an un-mounted vacuum bottle are
normally-closed, because the outside air pressure
pushes against the flexible bellows. For contactor
duty, the contacts must be open when the operating
magnet is not energized. Therefore, the contacts of
the vacuum bottles must be held apart mechanically
against the air pressure when used in a contactor.
In the SL contactor, all of the bottles are held open
by two kickout springs on the front of the contactor.
The kickout springs press against the moving
armature and crossbar and thereby force the bottles
into the open contact position. Note that in the open
position, the crossbar is pulling the moving contacts
to hold them open.
Up to an altitude of 3300 feet, the contactor is
designed to tolerate normal variations in barometric
pressure. Special factory modifications are required if
the contactor is to be applied at high altitude.
Contact the factory if the contactor will be applied at
elevations above 3300 feet.
The contactor is closed by energizing the contactor
control board with the appropriate control voltage at
terminals 1 and 2. The control board rectifies the
input voltage and applies a pulse width modulated
DC output voltage to the coil. The output voltage is
approximately full voltage for the first 200
milliseconds after energization, during which time the
contactor closes and seals. The output voltage is
then automatically reduced to approximately 15 VDC
to maintain the contactor in the closed position.
The coil core is magnetized which rotates the
armature shaft, armature, and crossbar. As the
armature moves toward the coil core, the main
contacts close. The crossbar continues to move an
additional distance (known as overtravel), which
allows for contact preload and wear. The overtravel
distance is the gap between the lower bottle nut and
the pivot plate as shown in Figure 2.
Fig. 2 Closed Contactor
When control power is removed from the control
board, the magnetically held contactor remains
closed for a preset time and then opens. The range
of time between the removal of control power and
contact opening is from 50 to 330 milliseconds
depending on the setting selected on the control
board. The time can be adjusted for such factors as
fuse coordination and voltage loss ride-through.
Unless otherwise specified, the factory default
dropout setting is 130 milliseconds, or approximately
8 line cycles (60Hz). To maintain proper
coordination with the starter power fuses, do not use
the 50ms setting.
A selectable dip switch is located on the control
board for setting the control voltage level and the
contactor dropout time. See Figure 3. The control
board must be removed from the cavity in the
contactor housing to gain access to the dip switch.
Table IIIa lists the available voltage settings and
Table IIIb lists the available dropout settings. These
tables are also printed on the back of the control
board. The control voltage setting should match the
starter control circuit voltage.
Bottle
Nuts
Pivot
Plate
Over travel
