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Figure 5-1. Stored-energy manual closing mechanism
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TM-5-6120-250-34 Substation Trailer Mounted 500 KVA AC 4160-416Y/240V 208Y/120V 3 Phase 50/60 Hertz Avionics Model 950-2200A Manual
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Pole ITnit Assembly
(5)  Check along the trip shaft for a mechanical
5-4. Separation of Front and Rear Frames
interference or connection between the overcurrent trip
a. To  repair  or  replace  contacts,  operating
device  and  the  trip  paddles.  Remove mechanical
mechanism, or the overcurrent devices, the front frames
connection if present, or if interference exists, use
must be separated from the back frame.
extreme care when removing front and back frames to
b. To  remove  the  circuit  breaker  from  its
avoid mechanical breakage of trip devices.
compartment see paragraph 2-21.
d. To  Reassemble  Front  and  Back  Frames.
c.  To Separate the Front and Rear Frames.
Reassemble in reverse order of preceding subparagraph
(1) The breaker contacts must be open with the
safety pin in place. See paragraph 5-3 a
CAUTION
(2)  Remove the two opening springs ion lower
The breaker should be fastened to a suitable
part of the breakers from the outside pole units.
(3)  Remove the clevis pin (16, fig. 5-2) from the
mounting  base  with  the  front  frame
center pole unit.
supported by a sling or hook as the bolts are
(4)  Remove the six nuts from the back frame
being installed.
using a socket wrench with an extension. These include
the two nuts at the top of the frame.
Section III. CIRCUIT BREAKERS
Observe the contact alignment and make sure all parts of
5-5. General
the mechanism move freely without bind- ing or
There are four type AK drawout air circuit breakers: one
excessive friction. If the breaker remains open or closed
main breaker (AK-3-50) and three feeder breakers (AK-2-
for a period of six months or more, arrangements should
50) each in its own metal compartment.  They are
be made to open and close it several times in succession.
connected mechanically and electrically to form a
It is important not to permit pencil lines, paint, oil or other
distribution load center. 'The drawout air circuit breakers
foreign material to remain on the insulating surfaces of
are easily removable to provide maximum accessibility
the breaker.  They may cause low resistance between
for maintenance.
The type AK removable breaker
points of different potential and result in eventual
elements consist of an interlock mechanism, the movable
electrical breakdown.  A complete contact in- spection,
portion of the primary and secondary disconnecting
including contact wipe and pressure, should be made at
devices, the breaker closing and tripping devices, and the
regular inspection periods and always after a known short
required protective devices. The breaker is equipped with
circuit current has been interrupted to determine whether
a positive mechanical interlock which prevents the
the contacts are worn or pitted, in which case they should
breaker from being racked in or out of the connected
be dressed or replaced.
position until after the breaker is tripped open.  This
CAUTION
interlock also holds the breaker trip free and prevents the
breaker from being closed while it is being racked in or
Never use cotton waste to wipe bearing
out of the connected position. The breaker fits on a
surfaces. The cotton raveling may become
drawout tray which is part of and rides within the breaker
entangled under the bearing surfaces and
compartment. The drawout features of the breaker are
destroy the surface of the bearing.
primary and secondary disconnect devices, and on the
rear vertical frame members of each side of the breaker
5-7. Circuit Breaker Contacts
are the racking cams (with the positive mechanical
interlocks. These cams are joined by a rod across the
a. Contact Sequence on the Horizontal Plane. The
back and are operated by the racking handle on the front
difference in the making of the arcing contacts on the
right side of the breaker (fig. 5-11.). All circuit breaker
same pole must be no greater than 1/ 32 inch; the
removable elements of the same type and rating may be
difference between arcing contacts on separate poles 1/
interchanged.
The following paragraphs give circuit
16 inch. If it is desired to ad- vance or retard the closing
breaker details.
of the main contacts of a pole, loosen the bolts holding
the adjusting plate 121, fig. 5-2) of that pole and slide
5-6. Inspection
plate to the left to advance contact closing, or to the right
to retard contact closing. Make this adjustment on the
At regular inspection periods the breaker should be
outer poles, using the center pole as a reference. Upon
operated manually (stored energy mechanisms with the
retightening adjustment plate bolts, make sure the
safety
pin
restraining
the
closing
springs).
5-3

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