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 i). 'The stationary arcing-contact assembly consists of
a set of parallel finger contacts (31, fig. 5-29, pin 1301,
locking tabs are turned up around bolt heads, locking
and compression springs (7), which provide continuous
the bolts securely in place.
contact pressure for the full travel of the contacts. Steel
CAUTION
springs (28) shunt the pivot pin to prevent possible
The following check must be done by operating the
pitting at the pivot point when interrupting high currents.
breaker slowly with the safety pin restraining the
c. The movable arcing-contacts assembly consists of
closing springs. See paragraph 5-3.
parallel contact anns (29) carried on two movable pivot
b. Contact Sequence in the Vertical Plane. This should
pins (24) and (11). The arcing contacts interleave the
he such that when the arcing contacts are just touching,
main contacts and pivot with them about the pin (11).
the intermediate contact gap should be at least 3/ 16
This relative motion is obtained by linkages from the
inch, the main contacts gap at least I / 4 inch. If the gap
upper shoulder pin (251 to the breaker mechanism.
is under the required minimum, it is usually possible to
d. The stationary main contact assembly includes main
form the arcing contacts and obtain the required
and intermediate contacts. The intermediate contact
dimensions. To form the arcing contacts, place a piece
surface extends beyond the main contacts and will,
of conduit approximately two feet long, over the contact
therefore, make before the main contacts and break
and form the contact either forward or backward. If the
after the main contacts.
proper dimensions are still not obtained, the movable
e. The movable main contacts pivot around a stationary
arcing contacts should be replaced.
pin (12), which holds them to the lower block. Motion is
CAUTION
obtained from a second pin 125), connected by an
If it has been necessary to make any adjustments
insulated link (18) to the breaker mechanism. In
while obtaining proper contact sequence, the
addition steel springs shunting the current from the
contact wipe and pressure must be checked, and
contact directly to the lower contact block, steel springs
adjusted if necessary.
1131 force the contacts against the pins to prevent
c. Contact Gap. When the breaker is open, the gap
pitting at the pivot point. The movable main contact
between the movable (29, fig. 5-2) and stationary
assembly also contains main and intermediate contacts.
contacts (31) should be between 2 5 / 8 and 2 3/ 4
f. In order to function properly, a definite amount of
inches. The gap may be adjusted by varying the
contact pressure and contact wipe must exist between
number of buffer spacers (20) on the crossbar. The
the movable and stationary contacts. Table 5-1 gives
locking nuts on the buffer bolts should be locked in such
the figures for contact pressure and contact wipe. Both
a position that the buffer bolt may be rotated freely.
wipe and pressure should be (checked during the
5-8. Pole ITnit Assembly
regular
inspection
period.
a. Each pole unit assembly consists of a set of arcing
contacts, a set of main contacts, the ac- tluating linkage
and the mounting base.
Table 5-1. For AK-50 Breaker
Main contact
Intermediate contacts
Arcing contacts
No of
Pres
Wipe
No of
Pres-
Wipe
No of
Pres-
Wipe
contacts
sure
('in)
contacts sure
(in)
Contacts
sure
IN
Per Pole
lb
(in)
Per Pole lb.
Per- Pole
(Ib)
3
55
4/64
1
55
2
31
12/ 64
to
to
to
to
to
65
7/ 64
65
43
18 / 64
The intermediate contact wipe should be at least 1/16 inch greater than the main contact wipe.
5-4
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