Motor starters consist of two devices—a contactor that completes the circuit to the motor and an overload relay that monitors the current the motor is drawing. … When a condition occurs that causes the motor to exceed the maximum load, the device opens the motor starter control circuit and the motor is turned off.
How does a motor contactor work?
Operating Principle of a Contactor:The current passing through the contactor excites the electromagnet. The excited electromagnet produces a magnetic field, causing the contactor core to move the armature. A normally closed (NC) contact completes the circuit between the fixed contacts and the moving contacts.
What is a starter contactor?
A contactor is really just an overgrown relay. It is but one component of a starter and is rated by voltage. The contactor applies voltage to a contactor coil to close the contacts and to supply and interrupt power to the circuit.
What is NO and NC In contactor?
In every control circuits and automation systems, logic is developed based on the open or closed state of switches, sensors or relays. … Normally open(NO) and Normally closed (NC) are terms used to define the states of switches, sensors or relay contacts under when its coil is not excited.
Can a starter be used as a motor?
In operation, a starter like all motors will generate heat due to electrical resistance in the windings. Its normal job as a starter requires it to run for a few seconds and then has minutes, hours, or days to get rid of the heat that builds up as turns the engine.
Why DOL starter is used up to 5 HP?
Direct-on-Line (DOL) Starter
This heavy current reduces as the motor accelerates to its rated speed. … For a large rating motor, ranging from 5 HP to 25 HP, oil immersed DOL starters are used which provides insulation against sparking on contact points and hence increases the life of starter.
When should you use a motor starter?
The contactor portion of a motor starter closes the contacts on all phases of the electrical current very quickly, minimizing the potentially dangerous effects in the event of an overload. Motor starters are sized to suit the motor and voltage of your specific application.
What does a motor starter have that a contactor does not have?
Contactors and motor starters are also distinct components. … The difference is that motor starters have one extra system or systems not found in contactors — an overload relay of some type to cut voltage input should that relay sense a motor-overload or thermally compromising condition due prolonged running overcurrent.
What is the most common cause of motor failure?
Winding insulation breakdown and bearing wear are the two most common causes of motor failure, but those conditions arise for many different reasons.
What are the basic components of a motor starter?
A 3-pole full-voltage magnetic motor starter is made up of the following components: a set of stationary contacts, a set of movable contacts, pressure springs, a solenoid coil, a stationary electromagnet, a set of magnetic shading coils, and the moving armature.
What are the two basic elements of a motor starter?
Contactor Construction and Operation. A magnetic motor starter has two basic parts: the magnetic contactor and an overload relay .