Electrical Practice

The run capacitor on a motor is used to a. increase torque b. increase horsepower c. decrease resistance d. increase amperage

a. Increase Torque

If a conductor is wrapped around the jaws of a clamp-on ammeter four times and the meter indicated 16 amps, the actual amperage would be a. 16 amps b. 8 amps c. 4 amps d. 2 amps

c. 4 amps

Capacitor Selection Rules

1) Voltage must be greater than or equal to listed voltage 2) Start capacitors must be rated +/- 20% of mFd listed 3) Run capacitors must be rated +/1 10% of mFd listed

Formula for capacitors in series

Total Capacitance = 1 / (1/C1 + 1/C2 ... + 1/C#)

Formula for capacitors in parallel

Total Capacitance = C1 + C2 ... + C#

All else being equal, which of the following wire sizes will carry the most current? a. 10 ga b. 14 ga c. 12 ga d. 18 ga

a. 10 ga

Low voltage controls are usually designed to operate at no more than a. 25V b. 80V c. 120V d.230V

a. 25 Volts

A high pressure control is usually located on the a. condensing unit b. evaporator c. cabinet d. blower

a. Condensing Unit

A low pressure control is usually located on the a. condensing unit b. evaporator c. cabinet d. blower

a. Condensing Unit

A set of contacts in a pressure control that close when the pressure increases are a. direct acting b. reverse acting c. dual acting d. none of these

a. Direct Acting - "closes on rise" - contacts close on an increase in pressure.

Ohm's law states a. E = IR b. E = PR c. R = IE d. I = RP

a. E = IR

Open motors are designed to operate at a given temperature rise as indicated on the motor nameplate. What does this mean? a. it indicates the temperature rise over the surrounding air of a motor when the motor is operating at full-load conditions. b. it indicates the temperature rise of the motor. c. it indicates the temperature drop of the surrounding air. it indicates the temperature drop of the motor at rest.

a. In indicates the temperature rise over the surrounding air of a motor when the motor is operating at full-load conditions.

The compressor oil safety control is an electro-mechanical control that operates on which two pressures? a. oil pump and suction b. oil pump and discharge c. suction and discharge d. oil and atmospheric

a. Oil Pump pressure & Suction pressure

What is impedance? a. opposition to alternating current flow b. electrical flow c. amperage d. electrical pressure

a. Opposition to alternating current flow

Two silicon-controlled rectifiers wired in reverse parallel with each other allows a. current flow in both directions b. current flow from the anode to the gate c. current flow from the cathode to the gate d. current flow in one direction only

a. current flow in both directions

What is the total capacitance of two 20-microfarad capacitors wired in series with each other? a. 5 mf b. 10 mf c. 20 mf d. 40 mf

b. 10 microfarad

How much resistance must be placed in a 220-volt circuit to limit the current to 2 amps? a. 55 ohms b. 110 ohms c. 30 ohms d. none of the above

b. 110 Ohms

Hot surface igniters operate on which of of the following voltages? a. 24 V b. 120 V c. 240 V d. about 8 to 10 kV

b. 120 V

What is the millivolt reading of a good thermocouple? a. 5 mv b. 15 mv c. 30 mf d 120 mv

b. 15 millivolts

Which of the following capacitors is the best choice to replace a 35 mf, 370 volt run capacitor? a. 35 mf, 330 volt b. 35 mf, 390 volt c. 30 mf, 440 volt 40 mf, 370 volt

b. 35 mf, 390 volt

What is the Btuh output of an electric heater rated at 15 kW? a. 51.15 Btuh b. 51,150 Btuh c. 5,115 Btuh d. none of the above

b. 51,150 Btuh

One horsepower is equal to _________ watts. a. 3.414 b. 746 c. 1.08 d. 1200

b. 746

A unit of power equal to one horsepower and delivered at the shaft of a motor is known as a. amperage b. brake horsepower c. horsepower d. voltage

b. Brake Horsepower

Which of the following is a safety control? a. thermostat b. high pressure control c. low pressure control d. humidistat

b. High Pressure Control

What is the purpose of the holding circuit in a magnetic motor starter? a. holds the main contacts open until the control circuit through the interlock is made. b. holds the main contacts closed until the control circuit through the interlock is broken. c. holds the main contacts open until the control circuit through the interlock is broken. d. holds the main contacts closed until the control circuit the interlock is made.

b. Holds the main contacts closed until the control circuit through the interlock is broken.

A motor is a _________ load. a. resistive b. inductive c. capacitive d. mechanical

b. Inductive

A voltmeter is connected into a circuit in which of the following ways? a. series b. parallel c. series-parallel d. delta

b. Parallel

Which of the following control settings is typically non-adjustable? a. set point b. range c. differential d. cut-in

b. Range

A high pressure safety control is a. direct acting b. reverse acting c. dual acting d. none of the above

b. Reverse Acting - opens on a rise or increase in pressure

When four diodes are constructed in a bridge circuit and alternating current is brought into the input of the bridge, the output of the bridge provides: a. half wave rectification b. full wave rectification c. pulsating AC d. none of the above

b. full wave rectification

When photons of light strike the surface of a typical cadmium sulfide photoconductive cell a. resistance increases b. resistance decreases c. cell produces voltage d. none of the above

b. resistance increases

A voltage imbalance is a problem associated with which type of motor? a. single phase motor b. three phase motor c. DC motor d. PSC motor

b. three phase motor

On a standard electro-mechanical thermostat, if the fan switch is in the "on" position, the indoor fan will a. run only when the thermostat is calling for the compressor to run b. run when the indoor temperature reaches set point c. run continuously d. none of the above

c. Run Continuously

What electrical-mechanical control would you use on a cap tube or automated expansion valve system to maintain the space temperature? a. dual pressure control b. low pressure control c. thermostatic control d. high pressure contorl

c. Thermostatic control

When the temperature of a negative temperature coefficient material increases, its resistance will a. remain the same b. increase c. decrease d. change by the square of the applied voltage

c. decrease

Doubling the voltage to a resistance will cause the power or watts to a. double b. triple c. quadruple d. remain the same

c. quadruple

The coil of a lockout relay is wired _______ with the contactor coil and in _______ with the contacts of the control it is protecting. a. series, series b. parallel, parallel c. series, parallel d. parallel, series

c. series, parallel

What is the total capacitance of two 20-microfarad capacitors wired in parallel with each other? a. 50 mf b. 10 mf c. 20 mf d. 40 mf

d. 40 microFarad

How are fuses sized? a. by amperage c. by microfarads c. by voltage d. both a and c

d. Both A and C - Amperage and Voltage

Capacitors are rated in a. Amperes b. Microfarads c. Volts d. both b and c

d. Both B and C - MicroFarards and Volts

Which of the following mathematical relationships is true of a motor's horsepower if the CFM of a blower were changed? a. HP changes directly proportional to changes in CFM b. HP changes inversely proportional to changes in CFM c. HP changes by the square of the change in CFM d. HP changes by the cube of the change in CFM

d. HP changes by the cube of the change in CFM

The term "nominal voltage" refers to a. the actual voltage b. the measured voltage c. the average voltage d. the listed voltage

d. Listed voltage

On a magnetic motor starter, the alloy piece that causes the motor starter to open and shut off the motor if too much motor current is drawn is called the a. holding coil b. heater c. relay d. trip armature

d. Trip Armature

Impedance in a circuit is the result of a. pure resistance b. inductive reactance c. capacitive reactance d. all of the above

d. all of the above

A low voltage control system that primarily operates on two levels of voltage is called a(n) a. analog system b. digital system c. alternating system d. DC system

d. digital system

The bimetal strip in a common non-programmable thermostat is the a. anticipator bimetal b. differential bimetal c. contactor bimetal d. none of these

d. none of these

Doubling the voltage to a fixed resistance will a. not change the current b. double the current c. triple the current d. quadruple the current

d. quadruple the current