
Motor Starter Contactors

Contactors are composed of a contact system, an electromagnetic system and an arc extinguishing device. They are electrically-controlled switches that are designed to connect to high-current load devices like electric motors. Contactors typically fit with normally-open contacts, so that the power to the load is shut off when the coil is de-engergized. They can control and suppress arcs produced when interrupting heavy motor currents.
Combination motor starters contain the motor starter, a disconnection device and a short-circuit protection device in a single enclosure. This provides an added level of protection from electrical faults that can cause motor overheating and damage.
Contactors vs Starters A contactor is an electrically-controlled switch similar to a relay. A starter is a combination of a contactor and an overload relay. A starter has relays that are both normally-open and normally-closed, while a contactor operates with only normally-open contacts. A starter uses overload relays to protect the motor from overcurrents by shutting the motor down to prevent overheating. A contactor applies voltage to a coil to close the contacts to supply power, and de-energizes the coil to interrupt power to the circuit. Therefore, a contactor does not have the overload protection options that a starter does.
Products
Motor control allows operational control of electrical motors in various environments. Motor control circuits provide a safe way to operate electrical motors. Back when motor control circuits were in their infancy, it would have been common to see a simple disconnect switch that would be used to turn on and off a motor. Depending on the size of the motor and how much voltage was required, operating this disconnect would have been dangerous, with a very high possibility of arcing or electrocution. Not to mention that when the disconnect was actuated, the large amount of inrush current would have damaged the motor over time.
In today's motor control circuits, there are a few common pieces of hardware. A circuit breaker is used to protect the motor and any hardware downstream. A contactor and an overload relay are connected together and function in tandem to allow for remote and safe operation of the motor. The contactor functions much like a relay, allowing for a smaller electrical circuit to remotely close the motor contacts, starting the motor. The overload relay is designed to protect the motor in the case of a prolonged overcurrent event. These two devices are wired in series, so that if the overload relay detects an overcurrent event, the contactor will open the motor contacts, shutting off power to the motor.
The other two most common types of motor control hardware are a soft starter and a Variable Frequency Drive (VFD). Both of these devices function in a similar way to the motor circuit with some added functions. The soft starter is designed to reduce large inrush current to the motor upon startup. This “soft starting” of the motor will prolong its life and allow for safer operation. The VFD performs the soft start functions, but also allows for speed control of the motor. This speed control is critical in many different environments and has made VFDs one of the most common and safe to use motor control circuits today.