circuits and controls
What is generally considered to be the maximum allowable (plus or minus) supply voltage variation?
5%
Three resistors are wired in series. Each has a value of 300 ohms. What is the total resistance of the circuit
900 ohms
How many watts of power are used by a heater operating at 460 volts and drawing 5 amps?
A. 2300 watts
Voltage can be calculated by:
A. I times R
An ohmmeter should never be connected to:
A. a live circuit
A ______________________may be used on a single phase induction motor to disconnect the start windings after the motor starts
A. Centrifugal switch CorrectB. All of these C. Potential relayD. Amperage relay
A device used to control a motor is a;
A. contactor.B. line starter. CorrectC. all of theseD. relay.
Electricity can produce
A. heatB. lightC. magnetism CorrectD. all of the above
A device used to control a motor is a
A. relayB. contactorC. line starter CorrectD. all of the above
How are fuses sized?
Amps & Volts
A transformer has 1000 turns of wire in the primary coil and 2000 turns in the secondary coil. If 120 volts are applied, the output voltage will be;
B. 240 volts
Utility companies usually supply residential homes with _________service.
B. 240V, single phase, three wire
A transformer has 1000 turns of wire in the primary coil and 500 turns in the secondary coil. If 120 volts are applied, the output voltage will be;
B. 60 volts
Contactors are rated according to the maximum amperage through the;
B. contacts
Contactors are rated according to the maximun amperage through the;
B. contacts
A step up transformer increases;
B. voltage
Capacitors are rated in;
B. microfaradsC. volts
Overcurrent can be caused by
B. overloadC. short circuitsD. ground faults
Direction of rotation of a single phase induction motor is determined by;
CorrectA. the direction of current flow through the start winding
What would be the result of three defrost heaters, each 12.5 ohms, wired in series to a 115 volt power supply, if the heaters were to supply a 360 watt heating load?
Heaters operate normally
When testing the windings of a single phase motor, Technician #1 says that the common and run terminals show the lowest resistance. technician #2 says that the pair of terminals with the highest resistance will indicate that the other terminal is the common. Who is correct?
both
Impedance in a circuit is the result of;
capacitive reactance.
To change direction of rotation of a three phase motor
change the position of any two supply wires.
A solenoid valve operates on the principle of
electromagnetism
When testing a motor with an ohmmeter, one winding show a 1000 ohm continuity to the motor frame. This is an indication of a good safety ground
false
Fuses are used to protect;
loads
when current flows, a_______________is produced around the conductor.
magnetic field
The thermal overload contacts on a line starter are usually __________reset.
manual
The ____________drawing illustrates where the components are located on the appliance..
pictorial
Like charges will
repel each other
The terminals T1,T2, & T3 are located at the ______ of a contactor.
top
How many switches can be connected to a contactor coil control circuit?
unlimited
How may switches can be connected to a contactor coil control circuit
unlimited
If contacts become dirty or pitted, it is acceptable to sand or file them as a permanent repair.
. False
What is resistance?
. Opposition to current flow
A capacitor opposes current flow in a circuit. This opposition is called;
. capacitive reactance
When testing a capacitor with an analog ohmmeter, the needle on the meter should;
. deflect towards zero then return to infinite reading
What is impedence?
Opposition to alternating current flow.
What is current flow?
The flow of electrons in the circuit
Transformers are rated according to;
VA at the secondary
Any material that will readily release electrons is called
a conductor
Capacitors are always connected ____________ to the start windings?
in series
An electron has
negative charge
Two 120 volt motors are wired in series, one is a 60 watt motor, the other is a 4 watt motor. The result would be;
neither motor would operate normally
What meter is used to bench check a motor for shorts or open windings?
ohmmeter