Adjusting Contact Wipe and Pressure

5-11. Replacement of Contacts

5-9. Measuring Contact Wipe and Pressure (fig.5-2).

a. Stationary Arcing Contacts.

a. Contact Wipe.

(1) Remove the plate by removing the two

(1) Remove arc quenchers, see TM 5-6120-

screws (32, fig. 5-2).

250-12.

(2) Loosen screws holding spring (leaf contact)

(2) With the breaker open, measure the

(28).

horizontal distance from the edge of the stationary contact

(3) Remove pin (30) freeing the stationary

to the stationary block behind it. ("B" dimension for arcing

contacts (31) and springs (7).

contacts; "C" dimension for main contacts).

(4) Install new springs and stationary arcing

(3) Close the breaker and repeat step (2). The

contacts in reverse order.

difference between the readings in step (2) and (3)

(5) Adjust contact wipe and pressure. See

determines the wipe of the contacts.

paragraph 5-10.

CAUTION

WARNING

The movable arcing contacts should be

Extreme care must be used not to trip the

replaced when the stationary arcing

breaker.

b. Contact Pressure.

contacts are replaced.

(1) Remove arc quenches, see TM 5-6120- 250-

b. Movable Arcing Contacts.

12.

(1) Separate front frame from rear frame. See

(2) Close the breaker and measure dimension

paragraph 5-4.

"B" figure 5-2.

(2) Remove pins (11. 24, fig. 5-2) and withdraw

(3) Open the breaker. Place a push-type scale

the contacts (29).

against the stationary arcing contacts (7) at a point

(3) Reassemble in reverse order of steps (2)

measured in line with the break between the contact stop

and (1).

(9) and the contact pivot block. Push the c contact

c. Stationary, Intermediate Main Contacts.

backward until dimension "B" recorded in step (2) is

(1) Remove stationary arcing contacts as

reached.

described in preceding step a.

(4) Read the scale. If the pressure is not within

(2) Remove screws (2, fig. 5-2) and remove

the requirements listed in table 5-1 refer to paragraph 5-

bracket which holds pin (4) in place.

10.

(3) Remove main and intermediate contact stop

5-10. Adjusting Contact Wipe and Pressure

19) which holds the lower part of the stationary contact.

a. Adjusting Center Pole. To obtain proper wipe and

Removal will be easier if the force on the contact

springs (8) is neutralized. This can be accomplished by

pressure, regulate dimension "A" in figure 5-2 to

operating the breaker with operating handle (with safety

increased to increase wipe and decreased to decrease

pin restraining closing springs ) slowly until the load on

wipe.

the contact stop is relieved.

(1) To change dimension "A" remove the clevis

(4) Loosen the hardware which fastens the

pin (16) and rotate the clevis as necessary.

upper stud (6) to the pole unit base until the contact

(2) To prevent overstressing the clevis threads

spring load on pin (4) is relieved.

dimension "A" should not exceed 3/ 16 inch and space "A"

(5) Remove pin (4) and screws (2) and lift out

should be filled with shims to 0.005 inch of being solid.

contacts (27) and (3).

b. Adjusting Outside Poles.

(6) Reassemble contacts in reverse order,

(1) With the proper center pole wipe obtained,

being careful to replace the intermediate contact (27) in

moving the cross-bar adjusting plate on the center pole to

the proper position.

the right will simultaneously increase the wipe on both

d. Movable Intermediate and Main Contacts.

outside poles; moving the adjusting plate to the left will

(1) Remove the movable arcing contacts as

have the reverse effect.

described in preceding step b

(2) To increase the wipe on either outside pole

(2) Loosen spring (13, fig. 5-2).

individually, move the crossbar adjusting plate of that

(3) Remove braid if present by removing screw

pole to the left; to decrease the wipe move the adjusting

at bottom of contact.

plate to the right.

(4) Slide link (18) to the side and off of pin (25).

CAUTION

(5) Slide pins (25) and (12) far enough to the

If the proper contact pressure does not

side to allow the movable intermediate contacts to be

exist when the contact wipe is within its

replaced.

limits, the stationary contact springs

(6) Reassemble parts in reverse order. Check

should be replaced.

contact wipe

and pressure

following

contact

replacement.

5-5