GE AK-2-50 - Measuring Contact Wipe; Measuring Contact Pressure

GEK-7303 Low Voltage Power Circuit . Breakers
Fig. 5 (8019408) Disassembled arc quencher- AKF outer poles.
1. Muffler Assembly
2.
Spacer Block
3. Inner Barrier
4. Cap
travel · of · the contacts. Steel springs (5) shunt
the pivot pin to
pr _event possible pitting at the
pivot point when interrupting high
currents. · On
earlier model breakers flexible braid leads were
used.
rhe movable ~rcing-contact a~sembly consists
of
parallel contact arms (4) carried on two mov-
·able pivot
pins (8) and (19). The arcing con.tacts
interleave the main · contacts and pivot with them
about pin (19).
This relative motion is obtained by.
linkages
from the upper pin (7) to the breaker
mechanism. . . ·
Th·e
stationary main contact assembly includes
main and
intermediate contacts. The intermediate-
contact surface extends beyond the main contacts
and will,
therefore, make before the main contacts
and
break after the main contacts. The number
of contacts
for each breaker rating is · given
in
Table I.
The movable main contacts pivof around a
stationary pin (18), which holds them . to the
lower ·block. Motion is obtained from a second
pin .(7), connected by an insulated link (12). to tl\e
breaker mechanism. In addition to ste · e1 springs
shunting the current from the contact · directly to
!the
lower contact block, steer springs (17) force
liiie
con~cts ag~nst the pins to prevent pitting
at the pivot pomt. The movable main contact
jassembly
also contains main and intermediate
!contacts.
5. Intermediate
Barrier
6. Outer Barrier
. 7. Side Plate
In order to function properly, a definite amount
of contact
pressure and contact wipe must exist
between . the movable and stationary contacts.
Table I gives the
figures for contact pressure and
contact wipe. Both wipe and
pressure should be
cpecked during the_
regular inspection period. -:
MEASURING CONTACT WIPE (fig. 6)
· 1. Remove arc quenchers (see REPLACEMENT
under
ARC QUENCHER). .
2. With the
breaker open, measure the hori-
zontal distance
from . the edge of the stationary
contact to the
stationary block behind it. ('.'B"
dim.
for arcing contacts, "C" dim. for .main
contacts). ·
3. Clo.
se the breaker and repeat item 2. The
difference between the readings in items 2 and 3
determines the wipe of the · contacts. For safety
reasons be extremely careful not to trip the
breaker. · . ·
MEASURING CONTACT PRESSURE
(Fig. 6)
1. Remove arc quenchers (see REPLACEMENT
UNDER ARC QUENCHER).
2. Close the
breaker and measure dimension
"B".
3. Open the breaker. Place a push-type scale