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magnetic/ thermal

? overload relays offer greater flexibility and quicker reset times than ? overloads because no heat is required for operation.

magnetic motor starter

A ? is a magnetically activated switching device (with overload protection attached) and is used to switch single-phase or 3-phase power for AC motor control and power for DC motor control.

overload

A motor ? condition most often results from the loss of a phase on a 3-phase system, operation of the motor with too much load, or low line voltage to the motor.The damage to a motor caused by an overload is proportional to the magnitude of the overload voltage and duration of the overload condition.

false

A motor is controlled by momentary contact START/STOP pushbuttons and a holding contact. If a power failure stops the motor, it will restart when power is restored.

electronic

A(n) ? overload relay monitors the current in the motor power circuit through the use of small built-in current transformers.

10

Class ? overload relay operation is often used with hermetically-sealed motors, submersible pumps, or motors with short locked rotor time capability.

20

Class ? overload relay operation is recommended for general applications.

30

Class ? overload relay operation is used with motors driving high inertia loads, where additional accelerating time is needed and the safe permissible locked rotor time of the motor is within the class performance requirements

true

Depending on the design of the control circuit, a motor controller with bi-metallic overloads could restart automatically. This could expose operation and maintenance personnel to hazards.

immediately restarts

During a power interruption, the contacts of a manual motor starter remain closed. When power is restored, the motor ?

manual motor starter

Exhaust fans, small drill presses, and commercial garbage disposals are some common examples of typical fractional horsepower motors that would be controlled by ?

electronic

Instantaneous reset ability, lower energy consumption, faster reaction times, adjustable range settings, and instant phase loss protection are advantages to using ? overload relays.

true

It is preferable to use a control voltage that is derived from the motor voltage source when possible so that both the control and the motor circuit will be de-energized when the motor controller safety switch is opened.

false

Melting alloy and Bi-metallic are the two types of magnetic overload relays.

series/ current

Most thermal and magnetic overload relays are connected in ? with the motor power circuit, so all ? flowing to the motor must flow through the overload.

time curves

NEMA and IEC overload relays respond to overload conditions based on ? .

True

Overloads are sized based on motor full load current (FLC), contactor size, the motor service factor (SF), ambient temperature and the class number requirement.

magnetic

Similar to a solenoid, the ? overload relay coil is wired in series with the motor power circuit. As the current Increases, the magnetic field increases lifting the solenoid piston upwards. When the current reaches the preset level, the piston assembly is raised enough to trip the normally closed contacts and open the control circuit.

electronic

The newest overload technology, ? overload devices, provides motor protection and control flexibility not available in the other two types of overload relays.

true

The overload protection device in the motor starter detects excessive over-current conditions in the motor by measuring the motor current through the contactor's power circuit.

false

Three types of overload relays, thermal, magnetic, and electronic, with the same operational principles, protect the motor from overload current.

true

When an overload condition exists, the overload contacts in the lower power motor control circuit de-energizes the contactors.

motor starter

When the contactor and overload protection are combined into a single device, the combination is a ? .

true

When using current transformers to measure and respond to motor overloads, the primary winding relies on the magnetic field generated by the motor power circuit conductors to induce a voltage in the secondary windings. The induced voltage will create a current flow that is directly proportional to the current flow in the motor power circuit conductors.

6/8

circuit protection, including fuses and circuit breakers located ahead of the motor starter, is designed to ignore the initial high inrush current at motor start up, which is typically ? to ? times the normal operating current.