The electrical contactor has been around for over 100 years dating back to the early 1900's and today's modern contactor, though design changes for safety and performance have occurred, has functionally remained the same as its predecessors. The basic unit is comprised of 3 power poles, L1, L2 and L3 of and these poles are normally open. As the need for a more diverse offering has risen, there are now 2 pole, 4 pole and even contactors up to 12 poles (mostly for lighting applications) that are manufactured today.
A magnetic contactor is one of the most simple pieces of electrical components in the market today. The function is simple: power is applied to the coil (this is referred to as the coil voltage), which creates a magnetic field that pulls the contactors armature together. This causes the 3 moving contacts to connect with the 6 fixed contacts thus allowing power to flow from the line side to the load side and onto the piece of equipment that is being operated.
There are endless applications that one would find a contactor being used to operate electrical equipment. For residential applications, 2 and 3-pole contactors are found in HVAC equipment, sewage pumps and outdoor lighting units. In the commerical arena, they can be found in countless applications, such as capacitor banks, isolation, assembly lines and operating motors and compressors.
When choosing the appropriate contactor for your application, it is important to determine both the horsepower and AMP rating needed along with the specific coil (control) voltage required. Confusion often occurs when trying to determine the AMP rating of a contactor as there are numerous different ratings based on the application. For example, the 2 most common ratings are AC-3 (inductive) and AC-1 (resistive). Manufacturers often specify their part numbers based off the AC-3 rating, which is the lower and more common rating to be used. For example, Schneider Electric manufacturers a part number LC1D32, which is a 32 AMP contactor (AC-3), but is also rated for 50 AMP (AC-1). It is important to know which rating is appropriate when sizing for a specific application.