I.B. 32-255-1G
Page 36
Effective 12/02
Figure 6-2 Vacuum Interrupter Showing Contact
Erosion Indicator with Breaker Open (Shown Here for
Clarity Purposes Only)
Figure 6-3 Vacuum Interrupter Showing Contact
Erosion Indicator with Breaker Closed (Indicators are
Checked Only When Breaker is Closed)
SOME DC HIGH POTENTIAL UNITS, OPERATING AS
UNFILTERED HALF-WAVE RECTIFIERS, ARE NOT
SUITABLE FOR USE TO TEST VACUUM INTER-
RUPTERS BECAUSE THE PEAK VOLTAGE
APPEARING ACROSS THE INTERRUPTERS CAN BE
SUBSTANTIALLY GREATER THAN THE VALUE
READ ON THE METER.
6-5 CONTACT EROSION AND WIPE
Since the contacts are contained inside the interrupter,
they remain clean and require no maintenance. However,
during high current interruptions there may be a minimum
amount of erosion from the contact surfaces. Maximum
permitted erosion is about 1/8 inch. To determine contact
erosion, close the breaker and observe the vacuum inter-
rupter moving stem from the rear of the breaker. If the
mark on each stem is visible, erosion has not reached
maximum value thus indicating satisfactory contact sur-
face of the interrupter. If the mark is not
visible, the pole unit assembly must be replaced (Figures
6-2 and 6-3).
The adequacy of contact wipe can be determined by
observing the vacuum interrupter side of the operating
rod assembly on a closed circuit breaker. Figure 6-4
shows the procedure for determining the contact wipe. If
the wipe is not adequate, the vacuum interrupter assem-
bly (pole unit) must be replaced. A field adjustment is
not possible. Refer to paragraph 7-3.2 for a replacement
procedure.
FAILURE TO REPLACE A POLE UNIT ASSEMBLY
WHEN CONTACT EROSION MARK IS NOT VISIBLE
OR WIPE IS UNSATISFACTORY, WILL CAUSE THE
BREAKER TO FAIL TO INTERRUPT AND THEREBY
CAUSE PROPERTY DAMAGE OR PERSONAL
INJURY.
6-6 INSULATION
Type VCP-W Circuit Breaker insulation maintenance pri-
marily consists of keeping all insulating surfaces clean.
This can be done by wiping off all insulating surfaces with
a dry lint free cloth or dry paper towel. In case there is any
tightly adhering dirt that will not come off by wiping, it can
be removed with a mild solvent or distilled water. Be sure
that the surfaces are dry before placing the circuit breaker
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