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I.B. 8926-1
CONTACT EVALUATION
Time of Service Contact Appearance
New The new contact has a uniform silver color.
Start of Service The contact surface will have a blue coloring. The geometric form of the contact is unchanged.
The sharp outer corners will be rounded with small silver beads. (See Figure 39.)
ntermediate Service to The coloring changes to brown or black with distributed small silvery white areas.
End of Service Life The surface has a finely chiselled appearance. Material transfer causes small peaks and
valleys in the contact button surface. (See Figure 40.)
Fig. 39 Normal Service Wear Fig. 40 End of Service Life
ABNORMAL WEAR CONDITIONS
Contact Appearance Cause
Curling and Separation Curling is usually a result of service that produces very high heat,
of Corner of Contact as under jogging or inching duty.
Irregular Contour or One corner of a contact may wear more quickly than the other three
Slantwise Wear corners. This wear is normally due to misalignment of the moving and stationary con-
tacts. Contacts should be replaced if it is apparent that one contact is nearly mak-
ing direct
contact with the contact carrier.
Large Beads of Silver Breaking an excessive current.
On Edges of Contacts
Welded Spot (Core of Making an excessive current. High frequency of operation, i.e., jogging.
Smooth, Shining Silver
Surrounded by a
Roughened Halo)
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