SECTION VIII. MAIN DISCONNECT SWITCH S120
5-45. GENERAL. Main disconnect switch S120 is a mechanical assembly used to buss the output of the generator set
to the output load terminals and to isolate the set from any external bus voltage source during maintenance. The switch
is opened or closed using the switch handle on the right exterior side of lower cabinet A. Repair of the disconnect switch
consists of disassembly to the extent required for replacement of a worn or damaged component.
5-46. MAIN DISCONNECT SWITCH S120 DISASSEMBLY.
Remove the main disconnect switch S120 assembly and switch handle assembly in accordance with the
Operator and Organizational Maintenance Manual.
Detach the operating mechanism assembly (1, Figure 5-35) from the disconnect switch frame (2) by removing
two hexagonal nuts (3) from the frame assembly. Do not remove hexagonal bolts (3, Figure 5-36) from the
mechanism assembly (1, Figure 5-35) at this time. Detach operating mechanism assembly (1) from the shaft
assembly (4) and remove shaft sleeve (5) if needed.
Disassemble operating mechanism assembly as follows: (1) See Figure 5-36. Remove sprocket assembly (14)
from the operating mechanism assembly by removing retaining ring (15) and sprocket washer (16). Using a gear
puller, remove sprocket (17) from drive lever assembly (11). Remove coupling key (18). Check sprocket (17)
for chipped worn, or broken teeth.
Remove two hexagonal nuts (1) from exterior sides of the housing plates (12 and 13) and remove housing
spacer studs (2) to separate outer housing plate (13) from inner housing plate (12). Remove right hand
latch (7) and left hand latch (6). Remove drive lever spacers (8 and 9). Remove drive spring assembly
(10) and drive lever assembly (11).
Remove hexagonal bolts (3) from outer housing plate (13) to remove housing spacer bushings (4) and
latch springs (5).
Disassemble disconnect switch assembly as follows:
Remove retaining rings (6, Figure 5-35) and pins (7) to detach connecting links (8) from the shaft assembly
(4). Discard retaining rings (6). Remove bearing plate (9) from frame (2), it needed, by removing hexagon
head bolt (10), lockwashers (11), and hexagonal nuts (12).
Remove three switch blade assemblies (13) from frame (2) by removing hexagon head bolts (14) and flat
washers (15) from top and bottom of the switch bases (18) and removing lockwashers (16) and hexagonal
nuts (17) from behind the frames.
Detach blades (19) from hinges (20) by removing elastic stop nut (21), pivot spring washers (22) and
hexagon head bolts (23).
Separate the two blades (19) and the connecting links (8) by removing hexagonal nuts (24), hexagonal
head bolts (25), and spacers (26). Remove cotter pin (27) from rivet (28) and remove flat washers (29)
and spring (30).
Detach jaw (31), arc chute support (32), and hinge (20) from base (18) by removing hexagon head bolts
Disassemble switch handle assembly as follows:
Remove chain (30, Figure 5-36) from housing. Remove cotter pin (19) from spacer (22) inside the housing
(32). Pull handle (20) away from housing (32) and remove two interlock discs (27), sprocket (24), and
spacers (22 and 23) from interior of housing (32). Remove two bearings (21) from bearing mounting holes
at side of housing.
Remove OPEN and CLOSED indicator plates (28 and 29) from housing (32).
Separate chain (30, Figure 5-36) halves, if needed, by loosening or removing turnbuckles (31).