The Many Types of Electric Starters
A Starter is a device that controls the use of electrical power to equipment, usually a motor. As the name implies, starters "start" motors. They can also stop them, reverse them, and protect them. Starters are made from two building blocks, Contractors and Overload Protection.
- Contactors control the electric current to the motor. Their function is to repeatedly establish and interrupt an electrical power circuit.
- Overload Protection protects motors from drawing too much current, overheating, and from literally "burning out".
Manual StarterThe manual starter is operated manually. Operating a manual starter is fairly simple and straightforward: a button or toggle (mounted directly on the starter) is pressed to start or stop the connected electrical equipment. Mechanical linkages from the buttons or toggle force the contacts to open and close, starting and stopping the motor. Often, a manual starter is the best choice for an application because it offers:
- Compact physical size
- Choice of enclosures
- Low initial cost
- Motor overload protection
- Safe and economical operation
Low Voltage Protection (LVP), which prevents automatic restarting of equipment after a power failure, is usually not possible with a manual starter. This means, if the power fails, the power contacts remain closed (toggle or button in ON position). When the power is restored, the motor automatically restarts itself. This could create a dangerous situation, depending on the application. Because of this feature, manual starters are generally used on smaller loads where low voltage protection is not needed.
Manual Starters, like the one pictured above have key switching elements that require manual operation. Notice the green switch on the Manual Starter above.
Magnetic Motor StarterThe other main type of starter is the AC magnetic motor starter. These starters are commonly used and often, the term Motor Starter is used in reference to the AC Magnetic Motor Starter. Motor starters offer some additional capabilities not available in a manual starter, most importantly, remote and automatic operation. In other words, the AC magnetic motor starter removes the operator from the immediate area. Like magnetic contactors, the motor starter depends on magnets and magnetism for its operation. These additional capabilities are due, in part, to the motor starters electromagnetic operation and the control circuit.
Magnetic Motor Starter CircuitryThe motor starter has two circuits: the power circuit and the control circuit. The power circuit runs from the line to the motor. Electricity passes through the contacts of a starter, the overload relay and out to the motor. The power (main) contacts carry the motor current.
The control circuit operates the contactor (on/off). The contacts that interrupt or allow the main current to flow to the motor are controlled by opening or closing the contacts in the control circuit. The control circuit energizes the coil creating an electromagnetic field that pulls the power contacts closed, thereby connecting the motor to the line. The control circuit makes remote operation possible.
The control circuit can get its power on one of two ways. If the control circuit gets its power from the same source as the motor, this is termed Common Control.
The other type is Separate Control. This is the most common form of control. In this arrangement, the control circuit gets its power from a separate source, usually lower in voltage than the motor's power source.
In addition, there are two ways to wire the control circuit. One common method of wiring the control circuit is known as Two-Wire. It uses a maintained contact type of pilot device-such as thermostat, float switch, or presence sensor. This circuit provides for an automatic operation (start-stop) of the load.
The other common method of wiring the control circuit is Three-Wire control. It uses momentary contact pilot devices and a holding circuit contact. The holding circuit contact is commonly an auxiliary contact on the starter or contactor. If power is interrupted, the circuit must be restarted by an operator or other intervening logic.
Magnetic Motor Starters, like the one pictured above, are capable of operating without the use of manual intervention. Therefore, the operator is still capable of starting the motor, although, from a remote location.
Motor Starter FeaturesAll motor starters share the following power control functions:
- Rated by current (amperes) or power (horsepower)
- Remote ON/OFF control
- Motor overload protection
- Starting and stopping (electrical life)
- Plugging and jogging (rapid making and breaking current)
Motor Starter VarietiesFour particular varieties of motor starters are: Across-The-Line, the Reversing Starter, the Multispeed Starter, and the Reduced Voltage Starter.
- Across-the-line or Full Voltage Non-Reversing (FVNR) is the most commonly used general purpose starter. This starter connects the incoming power directly to the motor. It can be used in any application where the motor runs in only one direction, at only one speed, and starting the motor directly across the line does not create any "dips" in the power supply.
- The Reversing Starter or Full Voltage Reversing (FVR) reverses a motor by reversing any two leads to the motor. This is accomplished with two contactors and one overload relay. One contactor is for the forward direction and the other is for reverse. It has both mechanically and electrically interlocked sets of contactors.
- The Multispeed Starter is designed to be operated at constant frequency and voltage. There are two ways to change the speed of an AC motor: Vary the frequency of the current applied to the motor or use a motor with windings that may be reconnected to form different number of poles. The multispeed starter uses the latter option to change speed.
- Reduced Voltage Starter (RVS) is used in applications that typically involve large horsepower motors. The two main
reasons to use a reduced voltage starter are to reduce the inrush current and to limit the torque output and mechanical stress on
Power companies often won't allow this sudden rise in power demand. The reduced voltage starter addresses this inrush problem by allowing the motor to get up to speed in smaller steps, drawing smaller increments of current. This starter is not a speed controller. It reduces the shock transmitted to the load only upon start-up.
The image above represents the Reversing Starter circuitry. The reversing magnetic motor starter features a forward and a reverse starter as part of the assembly.
Starter Video Overview