| Across-The-Line
| The most commonly used general purpose starter. This starter connects the incoming power directly to the motor. |
| Ambient
| The environmental conditions around a given piece of equipment, such as a motor. The air temperature around a motor is called the ambient temperature. |
| Arcing
| A condition where high voltage leaps across the open space between the contacts of a switch. |
| Armature
| A component of a magnetic contactor that holds the movable contacts. |
| Bimetallic Strip
| A strip of two dissimilar metals that does the work of tripping the relay on an overload in a bimetallic overload relay. |
| Common Control
| A control circuit that gets its power from the same source as the motor. |
| Contact
| The parts of a contactor that actually make and break the electrical connection. |
| Contact Bounce
| A condition caused by the contacts of a contactor slamming against each other and rebounding, causing a bouncing action. |
| Contactor
| An operating device which connects or disconnects the motor from the power supply. The term is used when the power poles are operated by an electromagnetic circuit, through the use of a coil and magnetic armature frame. |
| Control Circuit
| The circuit that controls a relay or contactor. |
| Double-Break Contacts
| A pair of contacts that can open a circuit in two places simultaneously |
| Electromagnet
| A magnet formed by a coil of wire with an electrical current running through it. |
| Eutectic Alloy
| A metal that has a fixed temperature at which it changes from a solid to a liquid. |
| Full Load Current
| The current required by the motor to produce full-load torque at the motor’s rated speed. |
| Heater Coil
| A sensing device that monitors the heat generated by excessive current, and by ambient temperature changes. |
| Inrush
| The amount of current drawn when a motor is first switched on. This can be 6 to 8 times the normal running current draw. |
| Knife Blade Switch
| The first device used to stop and start an electric motor. These were levers that would drop a strip of metal onto a contact to make the electric circuit. |
| Load
| The device being powered, such as a motor or heater. |
| Locked Rotor
| A condition that occurs when a motor is so overloaded that the rotor cannot turn, no matter how much current it draws. |
| Locked Rotor Amps
| The maximum amount of current a motor can draw when it is so overloaded that the rotor cannot turn. This is generally enough current to cause the insulation to fail and the motor to burn up. |
| Low Voltage Protection
| In a three wire control setup, when the voltage on L1 - L2 drops to a low value, and is then restored, the contactor will remain open. |
| Motor Service Factor
| The amount of extra horsepower a motor can generate without overheating. This is typically expressed as 1.15. |
| Multispeed Starter
| A starter designed to be operated at constant frequency and voltage. It uses a motor with windings that may be reconnected to form different numbers of poles to change speed. |
| Overload
| The application of excessive load to a motor. |
| Overload Protection
| A device or system that prevents an electric motor from drawing too much current, overheating, and literally “burning out.” |
| Overload Relay
| A relay that responds to electrical overloads and operates at a preset value. |
| Oxide
| A build-up that forms over time on contacts that are repeatedly opened and closed. |
| Power Circuit
| The part of a relay that actually provides power to the output component (such as a motor). |
| Reduced Voltage Starter
| A starter used in applications that typically involve large horsepower motors. It is used to reduce the inrush current and limit the torque output and mechanical stress on the load. |
| Reversing Starter
| A starter that reverses motor direction by reversing any two leads to the motor. |
| Separate Control
| A control circuit that gets its power from a separate source, usually lower in voltage than the motor’s power source |
| Solid State
| No moving, mechanical parts. |
| Starter
| A device that controls the use of electrical power to equipment, usually a motor. |
| Synchronous Speed
| The speed at which a motor is designed to run. |
| Trip (Tripping)
| The action an overload relay takes to protect a motor. |
| Trip Class
| The maximum time in seconds at which the overload relay will trip when the carrying current is at 600% of its current rating. A Class 20 relay will trip in 20 seconds or less. |
