45
Table 33. Wear of contacts
Simple wear Peeling wear Transiting wear Crack wear Mode
Conditions of
contacts
replacement
General wear.
When the contact over
travel, thickness of
moving contact or
thickness of fixed
contact become less
than the allowable
values given in Table
34, replace the contacts.
This wear takes place in
applications including
inching. When the
contact area becomes
less than 50% of the
whole area, replace the
contacts.
This wear is often found
in DC application.
When the area of a
transiting part is less
than 30% of the entire
contact area, remove
the transited projection,
and the contact can be
re-used.
This wear is found in
case of large-capacity
models over 100A
frame. When the area
of crack is more than
30% of the entire area,
replace the contact.
Remark: The contact over travel is the amount of movement of the insulated crossbar from the
beginning of contact of the moving and fixed contacts to the complete end of their
contact.
Table 34. Allowable minimum over travel and allowable minimum thickness of contacts
Allowable min.
thickness of
contact (mm)
Frame
Allowable
min.
over travel
(mm)
Moving
contact
Fixed
contact
Measuring method of over travel
H8C 0.5 0.6 0.6
H10C,11,12
HS10 0.5 0.6 0.6
H20,HS20 1 0.3 0.3
H25,HS25 1 0.3 0.3
H35,HS35 1 0.3 0.3
H50,HS50 1 0.3 0.3
H65C 1 0.5 0.5
Measure the position of operational
indicator at the front of contactor
with slide calipers.
Measure the position, a, of the
operational indicator when contact is
started by manual closing, and the
position, b , of the operational indi-
cator when the coil is excited, then
find the over travel.
Over travel = b - a
H80C 1 0.5 0.5
H100C 1 0.5 0.5
H125C 1 0.5 0.5
H150C 1 0.5 0.5
H200C 1 1 1
H250C 1 1 1
H300C 1 1 1
H400C 1 1 1
After the power of main circuit is turned
off, the coil is excited and contactor is
closed, remove the cover and look at the
hole on spring holder.
; Where the opposite side can be
seen through hole, the amount
of over travel is more than the
allowable value and contactor
can be used.
; Where the opposite side can
not be seen through hole, the
amount of over travel is less
than allowable value, then
replace the contacts.
H600C 2 1.5 1.5
Measure the position of operational indicator of auxiliary contact
assembly in the same manner as (A).
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