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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

bimetal overload device
an overload device that employs a bimetal strip as the actuating element. The bimetal strip consists of two metals bonded together. When heated, the bimetal strip will bend due to the different coefficients of linear expansion of the two metals. The bending operates a set of contacts that automatically removes the affected
load from the source of electrical power.
See overload relay
Coulomb, Charles (1763-1806)
Born: Angouleme, France
Coulomb is best known for his study of electric charge and magnetism resulting in Coulomb's Law, as well as his studies in friction. Coulomb also invented the torsion balance in 1777. He used this device in many experiments. Coulomb began his career in the military, but resigned when the French Revolution began. His experience as a military engineer involved him in a wide variety of different projects. It also gave him time to continue his own experimental work.
Coulomb's law states that the force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between the two charges. Coulomb is honored by having his name used as the unit of electric charge, the coulomb.
electronic overload device
an overload device that employs an electronic circuit to sense motor voltage and current for the purpose of providing precise motor overload protection. See also overload heater, overload relay.
eutectic alloy overload device
an overload device that employs a melting alloy as the actuating element. See also overload heater, overload relay.
magnetic overload
an overload sensor in a motor controller used to shut off the motor in event of an over current condition. With a magnetic overload, the sensor uses a magnetic coil to sense the overload condition, then trips the overload contact(s).
See overload relay
overlap angle

See commutation angle
overload heater
a term used to describe the thermal sensors that detect motor overload currents. Usually located on the motor starter, the heaters cause the overload relay to operate.
overload protection
a protective device which opens the circuit to a piece of electrical equipment or power line in the event of current exceeding the upper design limit.
overload relay
a device designed to detect and interrupt motor overload conditions.

Motor overload relays may be actuated by thermal (temperature), magnetic (current), or electronic (voltage and current) sensors.