Electric Motor Control Basics - Book - Page 9
Industrial Control Basics: Part 1, Contactors
The Life Expectancy of a Contactor or Contact Life
The life expectancy of a contactor or its “contact life” is one of the biggest concerns of
a user. It is natural that the contacts are being opened and closed more frequently, the
life of the contactor will decrease. The opening and closing of the contacts create an
electric arc, which generates additional heat. The continued production of these arcs
can damage the contact surface.
Furthermore, the electrical arcs cause pitting and burn marks, which eventually blacken
the contacts. However, the black deposit or oxide on the contacts make them even
more capable of conducting electricity efficiently. Nevertheless, when the contacts get
worn out and corroded to a large extent, then it is necessary to replace them.
Thus, the faster the contact closes, the quicker the arc extinguishes. This in turn helps
to increase the life of the contact. The latest contactor versions are designed in such
a way that they close very quickly and energetically. This causes them to slam against
each other and produce a bouncing action as they rebound. This action is known as
contact bounce. The contact bounce phenomenon creates a secondary arc. It is not only
important to close the contacts quickly, but also to reduce the contact bouncing. This
helps reduce wear and secondary arcing.
Industrial Control
Basics:
Part 1, Contactors
Industrial Control
Basics: Part 2,
Overload Relays
Industrial Control
Basics: Part 3,
Starters
The Benefits of Type E/F
Motor Protection
Circuit Breakers
Basic Pump Control:
Three Phase DOL Starter
Control of an Electric Pump
Applying Motor Control
in a Wastewater
Application
NEMA vs IEC Motor
Controls
Understanding
IP Ratings
09
