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Starters - Basic Properties, Terminology and Theory

What is a Starter?
Starter is made up of a controller, or contactor, and overload protection. A starter lets you turn an electric motor, or motor-controlled electrical equipment, on or off while providing overload protection. It represents another evolution in control.
There are two main types of starters: the manual starter and the magnetic motor starter.
Manual Starter
A manual motor starter is operated manually. Operation is fairly simple and straightforward: press a button or toggle that is mounted directly on the starter 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.
A manual motor starter offers:
  • Compact physical size
  • Choice of enclosures
  • Low initial cost
  • Motor overload protection
  • Safe and economical operation
Low Voltage Protection (LVP), prevents automatic restarting of equipment after a power failure, is usually not possible with a manual starter. This means of the power fails, the power contacts remain closed (toggle or button in ON position). When power is restored, the motor automatically restarts itself. This could create a dangerous situation, depending on the application. Because of this, manual starters are usually used on smaller loads where low voltage protection is not needed. This is an advantage for applications like pumps and blowers where the motor should run continuously and restart automatically.
Magnetic Motor Starter
The term AC magnetic motor starter is used many times interchangeably with the phrase motor starter because it is the most commonly used motor starter. Magnetic motor starters rely on magnets and magnetism for its operation. It has additional capabilities due to the motor starter's electromagnetic operation and the control circuit. Its most important features include remote and automatic operation.
The magnetic 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). Opening or closing the contacts in the control circuit interrupts or allows the main current to flow to the motor. 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 gets power in one of two ways. If the control circuit gets power from the same source as the motor, it's called Common Control. The other type of power is called Separate Control. Separate Control is the most common form of control and it gets power from a separate source, usually lower in voltage than the motor's power source.
There are also two ways to wire the control circuit. The more common method is known as Two-Wire. It uses a maintained contact type of pilot device - such as a thermostat, float switch, or presence sensor. This circuit provides for automatic operation (start-stop) of the load. The other method is Three-Wire control. Three-wire control 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 circuit power is interrupted, an operator or other intervening logic restarts the circuit.
All magnetic motor starters share these 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)
There are four types of magnetic motor starters and they include Across-the-Line, Reversing Starter, Multispeed Starter, and Reduced Voltage Starter.
Across-the-Line
This motor starter is also known as full voltage non-reversing (FVNR) and is the most commonly used, general purpose starter. It connects the incoming power directly to the motor. It's used in any application where the motor runs in only one direction, at only one speed, and starting the motor directly across the line without any "dips" in the power supply.
Reversing Starter
Another term for this starter is full-voltage reversing (FVR) because it reverses a motor when any two leads to the motor are reversed. 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.
Multispeed Starter
Designed for operation at a constant frequency and voltage. There are two ways to change the speed of an AC motor with this starter:
  1. Vary the frequency of the current applied to the motor
  2. Use a motor with windings with the ability for reconnection to form different numbers of poles
The multispeed starter uses the latter option to change speed.
Reduced Voltage Starters (RVS)
Used in applications that involve large horsepower motors. The two main reasons to reduce a reduced voltage starter are:
  1. Reduce the inrush current
  2. Limit the torque output and mechanical stress on the load
Power companies often won't allow this sudden rise in power demand. The reduced voltage starter addresses this inrush problem 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 common acronyms when dealing with starters are NEMA and IEC. These are organizations that recommend design and testing standards for electrical devices. It is important to note that neither organization performs actual testing of equipment. One standard is not necessarily superior to the other just different.
NEMA is the National Electrical Manufacturers Association. It has headquarters in Washington D.C., and associated with equipment used in North America. NEMA devices are built to a high level of perfection for use in a variety of applications. Because of their conservative ratings, NEMA devices are used in almost any application. Since they are less application sensitive and more durable, NEMA devices are frequently larger and therefore more expensive than IEC devices.
IEC is the International Electro-technical Commission. Headquarters in Geneva, Switzerland, it is associated with equipment used internationally. IEC devices are commonly used in OEM machines where specifications are known and not likely to change. Because of their greater application sensitivity, IEC devices sometimes require more care in selection than NEMA devices. An increasing number of control products are manufactured to IEC standards and conventions.
AC Motor Starters are available in reversing or non-reversing IEC or NEMA types. Depending on the requirements, horsepower can reach up to 800 @ 240V. Amps for starters go up to 2250. Before making your final selection, consult a motor application specialist.
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