GE Industrial Solutions Power-Vac ML-20 Mechanism - Manual (Page 11)

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SECTION 8—Dimensional Checks
With the breaker closed and the gag plate installed, perform
the following dimensional checks.
8.1—Primary Contact Erosion
In the closed position, the erosion marker (1, Figure 6) below
the bus bar is aligned with a reference mark on the
interrupter’s movable stem. As contact erosion occurs, the
erosion mark will move upward away from the erosion
pointer. When the seribed band on the interrupter’s movable
stem is completely above the top surface of the pointer, 1/8
inch erosion has occurred and the interrupter should be
replaced.
8.2—ML-20 Wipe Spring Compression
With the breaker closed and the closing spring gagged,
measure with a feeler gauge and record the distance between
the bellville washer and the trunion between the bell crank
arms.
8.3—Contact Gap
The method of measuring the contact gap is as follows: With
the breaker in the open position, the closing springs charged,
and the closing spring gag plate installed, apply a piece of
masking tape to the surface of the operating rod insulator as
shown in Figure 7. Using a reference block, make a mark on
the tape near the top on all three poles. It is also advisable to
put a reference mark on the tape to identify to which pole the
tape is applied. Remove the closing spring gag plate and close
the breaker. Using the same procedure as above, re-mark the
tape. This new mark will be near the bottom of the tape. Trip
the breaker, remove the tapes and re-apply them to a flat
surface. Measure the distance between the two lines.
A caliper will give an accurate reading of the contact gap,
Dimension G: The gaps must be between the 0.655 inch
maximum at the center pole and 0.595 inch minimum at the
outer poles. It is not necessary that all readings correspond. A
typically adjusted breaker will have more gap and wipe on the
center pole than on the outside poles.
The close coil and trip coil plunger gap dimensional checks are
made in the operating mechanism which is accessible from
the bottom. To accommodate these checks, the breaker
should be turned on its right side resting on two-by-four wood
blocks. DO NOT use the portable breaker lift truck.
CAUTION: DO NOT ALLOW ANYTHING TO COME IN
CONTACT WITH THE INTERLOCK ROLLER (4, Fig. 18) ON
THE RIGHT SIDE OF THE MECHANISM.
Figure 7 Contact gap