A motor starter is an electrical device that is used to start and stop the electric motor. It is used in various applications such as pumps, compressors, conveyors, and others. The motor starter consists of two components: the contactor and the overload relay. The contactor is an electrical switch that is used to connect and disconnect the motor from the power source, and the overload relay is used to protect the motor from overload conditions.
Components of 120v Motor Starter
A 120v motor starter consists of the following components:
- Contactors
- Overload relays
- Transformer
- Fuses
- Push-buttons and pilot lights
Contactors
The contactor is the core of the motor starter. It is an electrical switch that is used to connect and disconnect the motor from the power source. It is operated by a control circuit that is connected to the push-buttons or other control devices. The contactor consists of three main parts: the contacts, the moving part, and the stationary part. The contacts are the electrical switches that are used to conduct the current. The moving part is the part that moves the contacts to connect or disconnect the circuit. The stationary part is the housing for the contacts and the moving part.
The contacts of the contactor are designed to handle a specific current rating. The current rating of the contacts should be higher than the full-load current of the motor to ensure proper operation. The contactor should also be selected based on the voltage rating of the motor and the control circuit.
Overload Relays
The overload relay is used to protect the motor from overload conditions such as excessive current or prolonged use. It is connected in series with the motor and is designed to open the circuit if the current exceeds the rated value for a certain time period. The overload relay consists of a bimetallic strip and a heater element. The bimetallic strip is designed to bend when the temperature exceeds a certain threshold, and the heater element is designed to heat up the bimetallic strip when the current exceeds the rated value. The combination of the bimetallic strip and the heater element provides the necessary protection for the motor.
Transformer
The transformer is used to step down the voltage from the power source to the control circuit voltage. The control circuit voltage is typically 120v or 24v. The transformer is connected in parallel with the contactor coil and provides the necessary voltage for the coil to operate.
Fuses
The fuses are used to protect the motor starter from short-circuit conditions. They are connected in series with the control circuit and are designed to blow if a short-circuit occurs. The fuses should be selected based on the current rating of the control circuit and the voltage rating of the motor starter.
Push-Buttons and Pilot Lights
The push-buttons and pilot lights are used to control the operation of the motor starter. The push-buttons are used to start or stop the motor, and the pilot lights indicate the status of the motor starter. The push-buttons and pilot lights are connected to the control circuit and are typically rated for 120v or 24v.
Wiring Diagram for 120v Motor Starter
The wiring diagram for a 120v motor starter is shown below:
| Component | Connection |
| Power Source | Connect the hot wire to L1 and the neutral wire to L2 |
| Transformer | Connect the primary side to L1 and L2, and connect the secondary side to A1 and A2 |
| Contactor | Connect the power source to the contactor terminals T1 and T2, and connect the motor to the contactor terminals T3 and T4 |
| Overload Relay | Connect the overload relay to the contactor terminals T2 and T3 |
| Fuses | Connect the fuses in series with the control circuit |
| Push-Buttons and Pilot Lights | Connect the push-buttons and pilot lights to the control circuit |
FAQ
What is a motor starter?
A motor starter is an electrical device that is used to start and stop the electric motor. It consists of a contactor and an overload relay. The contactor is used to connect and disconnect the motor from the power source, and the overload relay is used to protect the motor from overload conditions.
What are the components of a 120v motor starter?
A 120v motor starter consists of contactors, overload relays, transformer, fuses, push-buttons, and pilot lights.
What is the function of the contactor in a motor starter?
The contactor is used to connect and disconnect the motor from the power source. It is operated by a control circuit that is connected to the push-buttons or other control devices.
What is the function of the overload relay in a motor starter?
The overload relay is used to protect the motor from overload conditions such as excessive current or prolonged use. It is connected in series with the motor and is designed to open the circuit if the current exceeds the rated value for a certain time period.
Why is a transformer used in a motor starter?
The transformer is used to step down the voltage from the power source to the control circuit voltage. The control circuit voltage is typically 120v or 24v. The transformer is connected in parallel with the contactor coil and provides the necessary voltage for the coil to operate.
What is the wiring diagram for a 120v motor starter?
The wiring diagram for a 120v motor starter consists of connections for the power source, transformer, contactor, overload relay, fuses, push-buttons, and pilot lights.
