Motor Starters and Contactors
13 Manual Motor Starters
Toggle
Small, fractional-horsepower motors are often controlled using a simple toggle switch. Most toggle-switch starters are rated at maximum 1 horsepower at 230V. They may be for single-pole or double-pole switching, and the ON and OFF positions are clearly marked on the lever.
The switch is similar in appearance to a standard light switch, but the main difference is that the motor starter has horsepower-rated contacts, which means that it can safely make and break the current drawn by the motor.
It also contains a thermal-overload device to provide overload protection by sensing any higher-than normal currents drawn by the motor. If a motor overload occurs, the excess current drawn by the motor causes the heater element to heat up, which automatically trips the switch contacts and breaks the circuit. The handle moves to the middle or tripped position, and after a cooling period, the toggle switch can be reset by pushing the lever into the fully off position and then switching it on again.
The compact construction of this manual-starter switch allows it to be installed directly on driven machinery and in tight spaces.
Pushbutton
Pushbutton motor starters are used for single-phase motors that are typically rated at a maximum 5 horsepower at 230V. They are similar in operating principle to toggle switches, except that they use two separate buttons to activate contacts. To start the motor, depress the start button so that it moves inward. A mechanical interlocking device forces the stop button outward. Once activated, these buttons remain in position until the opposite button is pressed.
If an overload occurs, the contacts can be reset by pushing firmly on the stop button after allowing for a cooling period.
Drum Switch
The drum switch is a rotary-action selector switch that is commonly used to manually control speed and to change the directions of motors. The handle in the centre at the top can be moved radially to various positions, turning a central shaft. The moving contacts on the shaft connect to a series of contacts on the perimeter of the drum.
When used to control single-phase motors, they are typically rated up to 3 horsepower at 240V or 1.5 horsepower at 120V.
The drum switch does not provide overload protection. Additional overload protection must be installed when using drum switches.
All manual starters have maintained contacts. If the power fails while the contacts are closed, when power is restored, the load will automatically re-energize. As a general rule, manual starters provide two-wire control and low-voltage release (LVR).
A device for making or breaking the connection in an electric circuit.
A device that controls the flow of electrical power to a motor. It is designed to safely start and stop a motor, and provide overload protection.
A set of contacts that has been designed to make or break the flow of current to a motor and can handle loads up to a specified amount of horsepower at a specific voltage. The size of contacts are determined by the size of the motor they are controlling.
A moderate and gradual rise in the value of current over a relatively long period of time that is caused by excessive amounts of current drawn by a motor due to too much load being put on the motor.
A physical barrier that is pushed into the path of one coil's armature by the movement of the adjacent coil in a forward/reversing motor starter.
Circuits with low-voltage release are designed to re-energize automatically when voltage is restored after a power outage. Examples include lights or the kitchen fridge.
