# Single Phase motors

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 Author: johnbowens ID: 111097 Filename: Single Phase motors Updated: 2011-12-26 00:51:21 Tags: single phase motors njatc Folders: Description: 4th year njatc single phase motors. ISBN: 978-0-8269-1982-3 Show Answers:

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1. Single phase motor types are named how? NJATC, Motors 2nd edition, Single Phase motors, PP 160
Single phase motor types are named for the method used to develop the rotating magnetic field.
2. what do all motors have? NJATC, Motors 2nd edition, Single Phase motors, PP 160
• All motors have a stator and a rotor.
3. A single phase motor and a 3 phase motor are nearly identical, except in what aspect? NJATC, Motors 2nd edition, Single Phase motors, PP 160
Single phase motors are different from 3 phase motors in that the windings in the single phase stator are placed 180 degrees apart, versus 120 degrees in three phase.
4. Both start and run windings (in the stator) in a single phase motor are in series or parallel? NJATC, Motors 2nd edition, Single Phase motors, PP 160
Parallel. So that the high resistance start winding can be disconnected by use of a centrifugal switch for instance.
5. The start winding in the stator on a single phase (2 pole) motor is placed how many mechanical degrees apart from the run winding and why? NJATC, Motors 2nd edition, Single Phase motors, PP 160
• 90 mechanical degrees apart to allow the motor to start in either direction.
6. Is the rotor in a single phase motor different from a 3 phase motor? How? NJATC, Motors 2nd edition; Single Phase motors, PP 160
No. Only the stator is different.
7. Explain the difference between the start and run windings on a single phase motor and how this facilitates starting. NJATC, Motors 2nd edition; Single Phase motors, PP 161
• Run winding has many turns and heavy wire = high reactance
• Start winding is smaller and has higher resistance
• This creates a phase difference between the two windings.
8. When the rotor is locked in place, the lack of rotation is the result of what? NJATC, Motors 2nd edition; Single Phase motors, PP 162
• The rotor becomes locked in place as a result of the stator and rotor fields being parallel to each other.
9. In a typical dual voltage motor, what is done with the run winding? NJATC, Motors 2nd edition; Single Phase motors, PP 163
The run winding is split into two sections.
10. Run windings are wired in what way for high and low voltage? NJATC, Motors 2nd edition; Single Phase motors, PP 162
Series is high voltage and parallel is low voltage.
11. Going to a series circuit in a single phase motor increases your voltage by two, and what happens to the impedence? NJATC, Motors 2nd edition; Single Phase motors, PP 162

As the voltage is doubled, impedence increases, and the current decreases, this means what for the cost of the installation?
Impedence increases by a factor of 4

An increase in voltage means less current and thus ampacity of conductors decreases, resulting in less cost in the installation.
12. To reverse the direction of most single phase motors, what is done? NJATC, Motors 2nd edition; Single Phase motors, PP 163
The two start leads are reversed.
13. What power source is required for a universal motor? Where are these motors used? NJATC, Motors 2nd edition; Single Phase motors, PP 163
Either AC or DC is used for universal motors and typically used in residential applications for high torque and speed. (Remember: residential is usually 1hp or less and single phase, fractional frame size motors)
14. A three phase motor is reversed using T1 and T3 leads as an industry standard for safety reasons, Leaving T2 permanently connected to L2 in case of Hi-leg. So A single phase motor reverses by switching the two start leads which are what? What color? NJATC, Motors 2nd edition; Single Phase motors
Single phase motors are reversed by switching T5 and T8 which are black and red.
15. A shaded pole is what? NJATC, Motors 2nd edition; Single Phase motors, PP 164
• A short circuited winding.
16. Shaded pole motors are typically what HP or less and have low or high start torque? NJATC, Motors 2nd edition; Single Phase motors, PP 164
Shaded pole motors are typically 1/20 HP or less and have low starting torque. (In us markets motors rated less the 1/20 HP are rated in watts. -Motor name plates)
17. How many stator salient poles are in a shaded pole motor's stator? NJATC, Motors 2nd edition; Single Phase motors, PP 164
2 or more divided into parts.
18. The shaded pole is at its strongest when what? NJATC, Motors 2nd edition; Single Phase motors, PP 166
The shaded pole is at its strongest when the flux is at its maximum, at 90 degrees behind the maximum current in the main pole.
19. Reversing a shaded pole motor is different from reversing a standard single phase motor how? There is a second method requiring what? NJATC, Motors 2nd edition; Single Phase motors, PP 166
The rotor must be removed from the housing and turned around.

A second method requires de-energizing a shaded pole and energizing the second one.
20. Slip in the shaded pole motor is a problem? T or F? NJATC, Motors 2nd edition; Single Phase motors, PP 166
Slip in a shaded pole is not a problem, as the current in the stator is not controlled by a counter voltage determined by the rotor speed, as in other types of single phase motors.
21. Define a split-phase motor. NJATC, Motors 2nd edition; Single Phase motors, PP 167
A split-phase motor is a single phase AC mtor that includes a run winding and a resistive start winding that creates a phase shift for starting.
22. Split phase motors are used where? what are thier HP ratings? NJATC, Motors 2nd edition; Single Phase motors, PP 167
Where starting is easy. from 1/30HP - 1/20 HP.
23. A split-phase motor has a stator constructed with what? What is used to disconnect the run windings from the start windings? NJATC, Motors 2nd edition; Single Phase motors, PP 167
The stator in a split-phase motor is constructed with both start and run windings, using a centrifugal switch to diconnect the run from the start windings.
24. A centrifugal switch is defined as what? NJATC, Motors 2nd edition; Single Phase motors, PP 167?
A switch that disconnects the start winding when the rotor reacheds a certain preset speed.
25. The centrifugal switch opens and closes at what percent of full speed? NJATC, Motors 2nd edition; Single Phase motors, PP 168
• The centrifugal switch opens at 75 percent of full speed and closes at 40 percent of full speed.
26. On a split phase motor the run and start windings have a usual phase difference of about how many degrees? What degree difference creates maximum starting torque? NJATC, Motors 2nd edition; Single Phase motors, PP 168
30 degrees is usual. Maximum starting torque would be at 90 degrees.
27. Reversing a split phase motor is done how? NJATC, Motors 2nd edition; Single Phase motors, PP 168
By reversing the start or run winding, but reversing the start winding is the industry standard.
28. A capacitor motor introduces capacitance into a single phase motor AC circuit to create what? NJATC, Motors 2nd edition; Single Phase motors, PP 168
To create a phase shift between the start and run windings.
29. What type of capacitors are used to start motors, and contructed how? NJATC, Motors 2nd edition; Single Phase motors, PP 169
AC electrolytic capacitors, contructed with two capacitors in opposite polarities.
30. What gives a capacitor start motor higher starting torque? NJATC, Motors 2nd edition; Single Phase motors, PP 170
Larger wire used in the start windings.
31. The capacitor start motor is also known as what? NJATC, Motors 2nd edition; Single Phase motors, PP 171
capacitor start induction run motor.
32. A capacitor-run motor has the start winding and capacitor connected in what way? NJATC, Motors 2nd edition; Single Phase motors, PP 171
In series at all times.
33. What is the advantage of leaving the capacitor in the circuit on a capacitor run motor? NJATC, Motors 2nd edition; Single Phase motors, PP 171
The motor has more running torque than a capacitor start or split phase motor.
34. How does the speed control of a capacitor run motor work? NJATC, Motors 2nd edition; Single Phase motors, PP 172
• By adding impedence to the run windings and increasing slip.
35. A capacitor run motor has the start and run windings connected one at a time? T or F? NJATC, Motors 2nd edition; Single Phase motors, PP 172
False. Capacitor run motors have the run and start windings connected at all times.
36. To reverse a capacitor run motor, what must be done? What is different between the windings? NJATC, Motors 2nd edition; Single Phase motors, PP 173
To reverse a capacitor run motor the capacitor is switched from one winding to the other. The start and run windings are identical, except the start winding is the one with a capacitor connected to it.
37. A dual capacitor motor is a.k.a. ? NJATC, Motors 2nd edition; Single Phase motors, PP 173
start and run motor.
38. A capacitor start and run motor has two capacitors connected in__________ and both in _________ with the start winding. NJATC, Motors 2nd edition; Single Phase motors, PP 173
A capacitor start and run motor has two capacitors connected in parallel and both in series with the start winding.
39. A capacitor start and run motor has a cetrifugal switch that does what? NJATC, Motors 2nd edition; Single Phase motors, PP 173
A capacitor start and run motor has a cetrifugal switch thatdesconnects the large capacitor that is in series with the start winding. The start winding is left in the circuit, creating more running torque than a capacitor start motor.
40. What is a bleed resistor used with and why? NJATC, Motors 2nd edition; Single Phase motors, PP 175
A bleed resistor is used with a start capacitor in rapid cycling because it does not fully discharge during start up, causing arcing without a bleed resistor.
41. A bleed resistor is used at what ohmic values and wattage rating? NJATC, Motors 2nd edition; Single Phase motors, PP 175
A bleed resistor is used at an ohmic value between 12K and 20k and are usually rated at 2W.
42. Motor wiring methods inside a terminal box include what? NJATC, Motors 2nd edition; Single Phase motors, PP 177
direct wire, terminal post, and terminal post with links.
43. The most common terminal box wiring method is what? NJATC, Motors 2nd edition; Single Phase motors, PP 175
The terminal post method is the most common terminal box wiring method.
44. The ends of a motor winding lead that require periodic changing have what type of lugs? NJATC, Motors 2nd edition; Single Phase motors, PP 177