Question 1

Contact surfaces are generally a alloy for better electrical conductivity.&#10;A)mercury&#10;B)tungsten&#10;C)copper&#10;D)silver

Accepted Answer

D

Question 2

The NEC requires that each phase of a motor be protected by an overload relay.

Accepted Answer

The NEC (National Electrical Code) requires that each phase of a motor be protected by an overload relay to prevent the motor from overheating and causing damage or even starting a fire. According to NEC 430.32, each phase of a motor must be protected by an overload relay to prevent overloading and overheating of the motor.

Question 3

Bimetal strip type overload relays operate on the principle that metals expand and contract with a change of .&#10;A)composition&#10;B)temperature&#10;C)force&#10;D)pressure

Accepted Answer

Bimetal strip type overload relays rely on the principle of thermal expansion, where metals expand and contract with a change in temperature. As the current increases, the bimetal strip heats up, causing it to deflect and trip the overload relay. Therefore, the correct choice is B) temperature. Bimetal strip type overload relays work based on the principle of temperature change causing the metals to expand and contract. As the current passing through a circuit increases, the temperature in the circuit also increases. This leads to the bimetal strip in the overload relay to bend or move, which eventually trips the circuit breaker and stops the flow of current. Therefore, the correct choice is B, temperature.

Question 4

enclosures are constructed of sheet steel and are provided with cover gaskets to exclude dust, lint, dirt, fibers, and flyings.&#10;A)NEMA 1&#10;B)NEMA 4&#10;C)NEMA 7&#10;D)NEMA 12

Accepted Answer

NEMA 12 enclosures are designed to provide protection against dust, dirt, and fibers, as well as provide some protection against water and oil. The enclosure is typically constructed of sheet steel and includes cover gaskets to further exclude contaminants. NEMA 1 enclosures provide little to no protection against liquids or even dripping water, while NEMA 4 and 7 enclosures are designed for more hazardous locations and may include features such as explosion-proofing and submergibility.

Question 5

Magnetic starters can be controlled remotely.

Accepted Answer

Magnetic starters can be controlled remotely through remote control devices or through a programmable logic controller (PLC). Magnetic starters can be controlled remotely through the use of remote control buttons or switches, which may be located some distance away from the magnetic starter itself. This allows for greater flexibility and convenience in controlling the equipment or machinery that the magnetic starter is connected to.

Question 6

overload relays react only to current excesses and are not affected by temperature.&#10;A)Electronic&#10;B)Thermal&#10;C)Magnetic&#10;D)Solid-state

Accepted Answer

Magnetic overload relays react solely to current excesses without being influenced by temperature changes, unlike thermal overload relays which respond to both current and temperature.

Question 7

The magnetic flux produced by the shading coil follows the direction of the flux of the main field.

Accepted Answer

The magnetic flux produced by the shading coil is actually designed to lag behind the flux of the main field, creating a phase difference that helps in producing a rotating magnetic field effect in shaded pole motors.

Question 8

Two-pole starters are used for .&#10;A)single-phase motors&#10;B)three-phase motors&#10;C)compound motors&#10;D)three-wire AC systems

Accepted Answer

Two-pole starters are typically used for single-phase motors. They provide the necessary starting torque and can be used with motors that have high starting currents. They are not commonly used for three-phase motors, compound motors, or three-wire AC systems. Two-pole starters are generally used for single-phase motors.

Question 9

Overvoltage produces low coil currents.

Accepted Answer

Overvoltage can cause high coil currents and potentially damage the coil. Overvoltage can actually produce high coil currents, since it can cause the coil to draw excessive power from the source voltage.

Question 10

All overload relays must allow some period of time before tripping to allow the motor to start.

Accepted Answer

All overload relays have an adjustable time delay feature that allows a motor to start and reach its full operating speed before tripping. This helps prevent false trips and protects the motor from damage due to overload. All overload relays have an inherent time delay before tripping to allow the motor to start and reach its normal running condition. This time delay is usually adjustable and can be set based on the motor's starting and running characteristics.

Deck 3: Magnetic Starters