Motor Starters
Manual starters are used to manually start three-phase motors using an electromechanical switch which, when activated, will open or close contacts to start or stop the motor. Low voltage protection, which prevents the motor from automatically restarting after a power failure, is usually not possible with manual starters. Therefore, they are better suited for smaller loads where low voltage protection is not needed.
Combination 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.
Non-reversing starters or across the line starters, are used with three-phase motors and contain only one contactor. The contactor opens and closes the power circuit to turn the motor on and off.
Reversing starters are used with three-phase motors and contain two motor contactors, instead of just one contactor. While one contactor is used to open and close the power circuit to turn the motor on and off, the second contactor is used for forward and reverse motor direction control.
Hybrid motor starters use solid-state semiconductor switches to start and stop motors. Because the semiconductor switches are non-mechanical, they can achieve up to ten times as many switching operations as their mechanical counterparts.
Subcategories
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.