Question 1

In one of the control methods to start a DC motor, a current-limiting resistor is provided to prevent coil .&#10;A)de energization&#10;B)energization&#10;C)burnout&#10;D)disconnection

Accepted Answer

Providing a current-limiting resistor in series with the coil of a DC motor limits the amount of current flowing through the coil and prevents it from burning out due to excessive heating. Therefore, option C (burnout) is the correct choice. The purpose of the current-limiting resistor is to prevent the coil from burning out due to excessive current flow. If there is no current limiting resistor, the coil could draw too much current and overheat, leading to burnout. Therefore, option C is the correct answer.

Question 2

DC arcs are greater than those due to AC.

Accepted Answer

DC arcs occur at higher voltage and have higher energy than AC arcs. This is due to the fact that DC voltage does not arrive at the zero point like AC voltage does, allowing for sustained arcing. This is because a DC arc is continuous and does not reverse direction like an AC arc, which can result in a less stable and smaller arc.

Question 3

Small DC motors can be connected directly across the line for starting.

Accepted Answer

Small DC motors with low power ratings can be connected directly to the line for starting without any damage or harm. However, it is not recommended for larger DC motors or those with higher power ratings as they may require adjustments to limit the starting current. Small DC motors can be directly connected to the line for starting as they have a low starting current which does not damage the motor or the power supply. However, it is important to note that this method should only be used for a short duration to avoid overheating of the motor or the power supply.

Question 4

Magnetic across-the-line control of small DC motors is very different from AC control.

Accepted Answer

Magnetic across-the-line control is typically used for AC motors, and not for small DC motors. DC motor control often involves electronic methods such as pulse width modulation (PWM) or variable frequency drives (VFDs). Magnetic across-the-line control is used for AC motors, while DC motor control utilizes other methods such as electronic speed controllers (ESCs) or pulse-width modulation (PWM) controllers.

Question 5

Some DC across-the-line starter coils have windings.&#10;A)dual&#10;B)no&#10;C)multiple&#10;D)plain

Accepted Answer

Some DC across-the-line starter coils have dual windings, which allows for lower starting current and reduced voltage drop during start-up. Some DC across-the-line starter coils have dual windings. This means that there are two separate windings, one for the run mode and one for the start mode, which allows for better efficiency and control of the motor's starting process.

Question 6

Fractional horsepower manual starters or magnetic contactors and starters are used for across-the-line starting of motors.&#10;A)large DC&#10;B)small DC&#10;C)large AC&#10;D)small AC

Accepted Answer

The answer of Fractional horsepower manual starters or magnetic contactors...

Deck 45: Across-The-Line Starting