Unit 17 Quiz Flashcards
A single-phase dual-voltage motor can be wired for 115V or 230V. When wired for 115V, the run windings are wired in ______ by the technician at the motor terminal box. If the motor is wired for 230V, the run windings are wired in ______.
Parallel
Series
The centrifugal switch is used to disconnect the start winding from the circuit when the motor reaches _____% of the rated speed.
75%
The difference between the calculated and actual speed of a motor is refereed to as motor ________.
Slip
On most shaded pole motors to reverse the direction of rotation, disassemble the motor and turn the _________ over.
Stator
The contacts in a potential relay are _______.
Normally closed
True or false: Three phase motors do not require a start or run capacitor.
True
True or false: A permanent split capacitor motor (PSC) has a start capacitor.
False
True or false: Torque is the twisting power of the motor shaft.
True
True or false: Voltage leads current in a capacitive circuit.
False
True or false: A PSC motor uses only a start capacitor.
False
True or false: Reversing a 3-phase fan motor will not affect the air flow.
False
True or false: The current magnetic relay has a set of normally closed contacts.
False
True or false: in a split phase motor, the start winding is taken out of the circuit to prevent the winding from overheating.
True
Capacitor start motors are often referred to as _________.
CSIR
The amount by which the current leads or lags voltage is the ______ angle.
Phase
The current magnetic relay terminals (CMR) are labeled/marked _______.
L,M,S
What energizes the coil in a potential relay to open the contact to take the start capacitor out of the circuit?
Electromotive Force
How do you switch the direction of rotation for a three-phase motor?
Switch the wiring position of anything 2 lines with each other
You are checking the coils on a potential relay and a current magnetic relay. Which relay has the higher resistance reading?
Potential Relay
In a CSCR motor, the start and run capacitors are wired in ______ with the start winding but are ______ to one another.
Series
Parallel
How does a split-phase motor differ from a permanent split capacitor (PSC) motor?
-PSC has a run capacitor
-Split may or may not have a run capacitor.
What terminals would you place your test probes on to see if the switch is open or closed on a current magnetic relay (CMR)?
LMS L&M = Coil. L&S for switch
Voltage at which contacts return to their original closed position.
Drop out voltage
Assists in starting the motor. Uses BEMF to cut out the start capacitor.
Potential relay
Rotor constructed of bars.
Squirrel cage rotor
Used to disconnect the start winding from the circuit when motor reaches 75% of the rated speed.
Centrifugal switch
Resistance to rotation
Slip
When contacts between terminals 1 & 2 of a potential relay will be opened.
Pick up voltage
Allows low friction rotation of the rotor. Reduces friction and heat generated by the motor’s moving and rubbing parts and surfaces.
Bearings
Voltage generated across the start winding by the motor’s rotor when it is up to about 3/4 speed.
Back Electromotive Force (BEMF)
Can be powered by 115V, 208V, or 230V. Rotation of the motor can be reversed by changing the connections in the motor terminal box.
Single phase induction motor
Similar to a split phase motor but does not have a start capacitor.
PSC motor
The diagram below is what type of motor?
Multispeed PSC
When hooking up the power wires to a three-phase motor, the correct color wire for L1 in the United States, according to the National Electrical Code (NEC) is _______.
Black
What happens when a capacitor with too much capacitance is used on a PSC motor?
May overheat/overload
When hoking up the power wires to a three-phase motor, the correct color wire for L3 in the United States, according to the National Electrical Code (NEC) is _____.
Blue
Calculate the speed of a 6 pole motor operating on 60 Hz.
When hooking up the power wires to a three-phase motor, the correct color wire for L2 in the United States, according to the National Electrical Code (NEC) is _____.
Red
How do you determine the direction of rotation for a single-phase and three-phase powered motor?
By orientation of the DataPlate. When facing the DataPlate, motor rotation is designated from this point of view unless data plate specifies direction of rotation.
What color is the neutral wire when used in a three-phase power supply?
White/Grey
**EXTRA CREDIT
1. you are getting power to the thermostat. You switch the thermostat to “Cool”, but nothing happens after the 5-minute delay. What are some things you can do to confirm the thermostat is broken?
Wire all lines together to see what activates. If something doesn’t activate, it’s broken somewhere.
EXTRA CREDIT
2. A step-up transformer has more windings in the ______ than the _____.
Secondary
Primary
EXTRA CREDIT
3. A motor uses a start and run capacitor. The start capacitor is rated at 45 uf and the run capacitor is rated at 5 uf. What is the total capacitance in the circuit when the motor is starting?
50 uf
EXTRA CREDIT
4. The switch in a potential relay is between terminals ____and____ while the switch in a current magnetic relay is between terminals ___ and ____.
2 & 1
L & S
EXTRA CREDIT
5. A motor that uses ball bearings may make too much noise that could be transferred through metal duct work. A motor using what type of bearings would be preferred?
Sleeve Bearings
