Test 1040 Flashcards
What does the term three phase refer to on three phase motors?
A system consisting of three alternating currents of the same frequency, which are offset in phase by 120 degrees.
Three phase motor will have the same resistance reading on across each winding. True or false?
True
Three phase motors require the assistance from capacitors. True or false?
False
What do we call it once a three-phase motor loses one voltage leg?
Single phasing
If air flow is restricted on a direct drive blower, what happens to the motor operating amperage?
It increases
How do you tell if a winding is short when using an ohmmeter on a motor?
Resistance reading is very low or zero
How do you tell if a winding is open when using an ohmmeter on a motor?
Resistance reading is infinity
How do you tell if a winding is ground when using an ohmmeter on a motor?
Resistance reading is low between winding and ground (0 ohms)
How do you tell if a winding is good when using an ohmmeter on a motor?
Resistance reading is within specified range
Checking a compressor single phase motor winding from common to start and getting an infinity reading means what?
The start winding is open
At what percentage of total RPMs is the capacitor taken out of the circuit in a motor using a centrifugal switch?
Approximately 75% to 80%
What is a symptom of an open start capacitor on a capacitor start motor?
The motor fails to start
Which motor winding has the highest resistance?
The start winding
What determines the RPMs of a motor?
The frequency of the power supply and the number of poles in the motor
If a capacitor produces 15 amps with a 230-volt AC power supply, what would the microfarad rating be?
Approximately 66 microfarads
Are the contacts of the potential relay normally open or normally closed?
Normally open
The coil of a potential relay is made up of many turns of wire and operates off what?
Current sensing
(Electromotive force)
What would be the best instrument to test water-soaked windings?
Insulation resistance tester
When reading motor winding resistance, what are we setting our meter to read?
Ohms
How do we reverse the rotation of a three-phase motor?
By swapping any two of the three phase connections
How do you identify the common, start, and run terminals in a motor?
Refer to the motor wiring diagram
1-2 has highest resistance then 2 is start
1 and 2 must be start and run
Remaining 3 must be common
1-3 yield lowest resistance which means 3 is common. 1 must be run bc lowest reading should be common to run and remaining terminal is start
A belt driven blower’s airflow will increase when the drive pulley diameter is increased or decreased?
Decreased
What is the max voltage imbalance we can have on a three-phase motor before service is required?
10%
Reading infinity on an ohmmeter when checking resistance means what?
There is an open circuit
What condition is the biggest safety hazard for the customer and technician when working on faulty condition? Short, open or ground?
Ground
On a split phase motor with a centrifugal switch is at rest, what condition is the switch in?
Closed
On a capacitor start motor with a centrifugal switch is at rest, what condition is the switch in?
Closed
What type of capacitor is encased in plastic?
Start capacitor
How would a faulty capacitor affect the operation of a motor?
It may cause the motor to fail to start or run inefficiently
1 phase, no capacitor, low starting torque, elect. Run, mag start
Shaded pole
1 phase, no capacitor, low torque, elect run, elect start
Split phase
1 phase, start cap, med torque, elect run, elect start
Capacitor start induction run
1 phase, run cap, med torque, elect run, elect start
Permanent split capacitor
1 phase, start cap, run cap, high torque, elect run, elect start
Capacitor start capacitor run
3 phase, high torque, N poles per phase
3 phase
