Section III. CIRCUIT BREAKERS

(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

5-4c

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

restraining

the

closing

springs).

5-3