Electrical Basics
A glossary of 12 electrical terms, formulas, and concepts commonly used in HVAC systems and certification exams.
Key Electrical Formulas
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Ampere (A)
Ampere is the electrical unit of electrical current. It measures the amount of electrical charge that flows in an electrical circuit per 1 second. 1A = 1C / 1s
Ampere-hour (Ah)
Ampere-hour is a unit of electric charge. One ampere-hour is the electric charge that flows in electrical circuit, when a current of 1 ampere is applied for 1 hour. 1Ah = 1A ⋅ 1hour One ampere-hour is equal to 3600 coulombs. 1Ah = 3600C
Farad (F)
Farad is the unit of capacitance. It represents the amount of electric charge in coulombs that is stored per 1 volt. 1F = 1C / 1V
Hertz (Hz)
Hertz is the unit of frequency. It measures the number of cycles per second. 1 Hz = 1 cycles / s
Kilovolt-amps (kVA)
Kilovolt-amps is a unit of power. 1kVA = 1kV ⋅ 1A = 1000 ⋅ 1V ⋅ 1A
Kilowatt-hour (kWh)
Kilowatt-hour is a unit of energy. 1kWh = 1kW ⋅ 1h = 1000W ⋅ 1h
Ohm (Ω)
Ohm is the electrical unit of resistance. 1Ω = 1V / 1A
Ohm's law formula
The resistor's current I in amps (A) is equal to the resistor's voltage V in volts (V) divided by the resistance R in ohms (Ω): V is the voltage drop of the resistor, measured in Volts (V). In some cases Ohm's law uses the letter E to represent voltage. E denotes electromotive force. I is the electrical current flowing through the resistor, measured in Amperes (A) R is the resistance of the resistor, measured in Ohms (Ω).
Resistance calculation
If we know the voltage and the current, we can calculate the resistance. The resistance R in ohms (Ω) is equal to the voltage V in volts (V) divided by the current I in amps (A): Since the current is set by the values of the voltage and resistance, the Ohm's law formula can show that: If we increase the voltage, the current will increase. If we increase the resistance, the current will reduce.
Volt (V)
Volt is the electrical unit of voltage. One volt is the energy of 1 joule that is consumed when electric charge of 1 coulomb flows in the circuit. 1V = 1J / 1C
Voltage calculation
If we know the current and the resistance, we can calculate the voltage. The voltage V in volts (V) is equal to the to the current I in amps (A) times the resistance R in ohms (Ω):
Watt (W)
Watt is the electrical unit of electric power. It measures the rate of consumed energy. 1W = 1J / 1s 1W = 1V ⋅ 1A