Motor Starters

Motor starters are used to start motors; they are comprised of an overload and a contactor. Motor starters have a safety circuit built into them which detects defects in the current that the motor runs on. Motor starters do two basic types of jobs which are switching the electric supply which supplies current to the motor and switching the motor off in case there is a fault in the electricity supply. There are single motor starters which have a couple of pole contactors while three-phase motor starters have three pole contractors. Poles mentioned in the above description denote a couple of contacts in the contactor module which are connected in order to supply electricity to the motor.

In an electric motor starter, an electromagnetic solenoid is used to bring two contacts to be brought into contact. In case of manually controlled motor starters, a spring loaded button is used. When a manual motor starter button is pushed, the action of pushing the button connects two contacts together. The spring uses the stored energy in it to break the circuit when a faulty current is detected in the power supply. An electric motor starter uses an electromagnet which is a soft iron core wound by a wire which is then supplied with electricity. Supplying electricity causes the formation of a magnetic force around the electromagnet. Therefore a contact is attracted towards it in which process it touches another contact and completes a circuit. An electrical signal is used to create the electromagnet and complete the circuit. This signal is produced by the action of a switch or a button.

Most motor starters contain an auxiliary contact which are a smaller set of contacts. The contacts give feedback to the other parts of the system that the motor starter is operating and that the circuit supplying power to the motor is complete. The smaller sets of contacts are situated near the normal contacts and operate identically along with them. Latching is a system in which the auxiliary contacts mentioned above overrides the action of the On Off button and the electromagnet remains as it is when current is supplied to it. Here another power switch situated separately controls switching the motor on and off.

Some motor starters have built in latching systems. In these motor starters, there are C, E, P and 3 terminals. The C terminal is neutral and the E terminal is hot. These terminals are always powered to supply the power required to run the motor. A current is to be applied to terminals 3 and P to start the rotation of the motor. If power to the P terminal is removed, the motor will stop unlike the 3 terminal where cutting its power doesn’t stop the motor. Depending on the type of the motor, the motor acts in different ways when motor starters supply electricity to them, a three phase motor starts rotating when supplied with electricity in a certain direction. In case of a DC motor the motor spins depending on the polarity of the coil windings.