HART-2431 Chapter 7 (Alterna ng Current, Power
Distribu on, and Voltage Systems)| Updated Rated A+ |
2026
What is direct current?
Direct current is an electron flow in only one direc on.
What is alterna ng current?
Alterna ng current is an alterna ng (back and forth) flow of electrons; that is, the electrons
reverse their direc on of flow at regular intervals.
What is direct current typically used for in the HVAC/R field?
Direct current has limited use in the industry; it is used mostly for refrigera on transporta on
equipment, electronic air cleaners, and electronic control components.
How is alterna ng current produced?
It is produced by cu+ng a magne c field with a conductor.
What is a sine wave?
A graphical representa on of alterna ng current; a graph showing the sine func on of all angles
from 0 to 360 degrees.
What is one cycle in alterna ng current?
When the conductor rotates through one complete revolu on, it has generated two
alterna ons or flow reversals. Two alterna ons (changes in direc on) equal one cycle (refer
again to Figure 7.1). One cycle occurs when the rotor, or conductor, cuts the magne c field of a
north pole and a south pole.
What is frequency?
The number of complete cycles per second of alterna ng current.
What is frequency measured in?
The frequency in known as hertz (Hz), but many mes it is referred to as cycles.
What is the most common frequency used in alterna ng current?
, In most loca ons in the United States, the common frequency is 60 hertz.
When does AC reach a peak?
Alterna ng current reaches a peak at 90 electrical degrees.
What is peak voltage?
When the voltage reaches its peak in an alterna ng current circuit.
What is the effec ve voltage? How is it determined?
Alterna ng current, with its many reversals and peaks, never peaks at a constant value. The
effec ve voltage is the working voltage of alterna ng current. The effec ve voltage is 0.707
mes the peak voltage.
How is effec ve amperage determined?
AC amperage is 0.707 mes the peak amperage.
What are the four basic voltage-current characteris cs available?
The four basic voltage-current characteris cs available are 240 Volt/single phase/60 hertz, 240
Volt/three phase/60 hertz, 208 Volt/three phase/60 hertz, and 480 Volt/three phase/60 hertz.
What is the abbrevia on for volts?
The V is the abbrevia on for volts
What is abbrevia on for phase?
Ø (Greek le?er phi) is the symbol for phase
What is the abbrevia on for Hertz?
Hz is the abbrevia on for hertz (which means the same as cycles).
What is the phase of an AC Circuit?
The number of currents alterna ng at different mes in an alterna ng current circuit. The phase
of an AC circuit is the number of currents alterna ng at different me intervals in the circuit.
What is single phase?
An electrical power supply that supplies two hot legs of electrical energy to a circuit.
What is three phase?
An electrical power supply that supplies three hot legs of electrical energy to a circuit.
Distribu on, and Voltage Systems)| Updated Rated A+ |
2026
What is direct current?
Direct current is an electron flow in only one direc on.
What is alterna ng current?
Alterna ng current is an alterna ng (back and forth) flow of electrons; that is, the electrons
reverse their direc on of flow at regular intervals.
What is direct current typically used for in the HVAC/R field?
Direct current has limited use in the industry; it is used mostly for refrigera on transporta on
equipment, electronic air cleaners, and electronic control components.
How is alterna ng current produced?
It is produced by cu+ng a magne c field with a conductor.
What is a sine wave?
A graphical representa on of alterna ng current; a graph showing the sine func on of all angles
from 0 to 360 degrees.
What is one cycle in alterna ng current?
When the conductor rotates through one complete revolu on, it has generated two
alterna ons or flow reversals. Two alterna ons (changes in direc on) equal one cycle (refer
again to Figure 7.1). One cycle occurs when the rotor, or conductor, cuts the magne c field of a
north pole and a south pole.
What is frequency?
The number of complete cycles per second of alterna ng current.
What is frequency measured in?
The frequency in known as hertz (Hz), but many mes it is referred to as cycles.
What is the most common frequency used in alterna ng current?
, In most loca ons in the United States, the common frequency is 60 hertz.
When does AC reach a peak?
Alterna ng current reaches a peak at 90 electrical degrees.
What is peak voltage?
When the voltage reaches its peak in an alterna ng current circuit.
What is the effec ve voltage? How is it determined?
Alterna ng current, with its many reversals and peaks, never peaks at a constant value. The
effec ve voltage is the working voltage of alterna ng current. The effec ve voltage is 0.707
mes the peak voltage.
How is effec ve amperage determined?
AC amperage is 0.707 mes the peak amperage.
What are the four basic voltage-current characteris cs available?
The four basic voltage-current characteris cs available are 240 Volt/single phase/60 hertz, 240
Volt/three phase/60 hertz, 208 Volt/three phase/60 hertz, and 480 Volt/three phase/60 hertz.
What is the abbrevia on for volts?
The V is the abbrevia on for volts
What is abbrevia on for phase?
Ø (Greek le?er phi) is the symbol for phase
What is the abbrevia on for Hertz?
Hz is the abbrevia on for hertz (which means the same as cycles).
What is the phase of an AC Circuit?
The number of currents alterna ng at different mes in an alterna ng current circuit. The phase
of an AC circuit is the number of currents alterna ng at different me intervals in the circuit.
What is single phase?
An electrical power supply that supplies two hot legs of electrical energy to a circuit.
What is three phase?
An electrical power supply that supplies three hot legs of electrical energy to a circuit.
