Electric Motor Control Basics - Book - Page 6
Industrial Control Basics: Part 1, Contactors
Different Types of Contactor Devices
1. Knife Blade Switch
Industrial Control
Basics:
Part 1, Contactors
Knife Blade Switch
Industrial Control
Basics: Part 2,
Overload Relays
Industrial Control
Basics: Part 3,
Starters
The Benefits of Type E/F
Motor Protection
Circuit Breakers
The knife blade switch was used earlier in the late 1800’s. It was probably the first
ever contactor that was used to control (start or stop) electric motors. The switch
consisted of a metal strip, which would drop onto a contact. This switch had a lever
for pulling the switch down or pushing it up. Back then, one had to level the knife
blade switch into the closed position by standing next to it.
However, there was a problem with this method of switching. This method caused
the contacts to wear out quickly, since it was difficult to manually open and close
the switch fast enough to avoid arcing. As a result of this, the soft copper switches
underwent corrosion, which further made them vulnerable to moisture and dirt.
Over the years, the size of the motors increased which further created the need for
larger currents to operate them. This created potential physical danger to operate
such high current carrying switches, thus leading to a serious safety concern.
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
06
