Benshaw Starter Overload Relays
Benshaw offers a complete suite of products for motor control and protection. At the core of their motor protection solutions are overload relays designed to prevent damage to three-phase and single-phase motors caused by excessive electrical current. These relays (more correctly referred to as starters with overload protection) serve two functions: They trip the motor circuit when dangerous overcurrents occur and when they don't stop tripping during a nuisance fault, and they also prevent phase loss and overheating of the motor.
Adjustable overload relays from Benshaw allow for fine-tuning the relay to the motor's protection requirements. Both thermal and electronic versions are available, providing application-based flexibility. The relays are straightforward to install and integrate with perfectly with control devices. Convenience and safety are taken care of in both manual and automatic reset options.
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Motor Control Basics
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.