Electrical Fundamentals for HVAC
AC/DC theory, single and three-phase power, motors, capacitors, transformers, contactors, and circuit protection.
- Apply Ohm's Law and basic electrical calculations
- Compare single-phase and three-phase power systems
- Identify motor types, capacitors, and starting methods
- Describe transformer operation and circuit protection devices
Lesson 1
Voltage, Current, Resistance & Ohm's Law
Fundamental Electrical Concepts
Three basic electrical quantities govern every HVAC circuit:
Ohm's Law
Ohm's Law states: Voltage = Current x Resistance (V = I x R). This fundamental relationship allows you to calculate any one value when you know the other two.
| Known Values | Formula | Example |
|---|---|---|
| I and R | V = I x R | 10A x 24 ohms = 240V |
| V and R | I = V / R | 240V / 24 ohms = 10A |
| V and I | R = V / I | 240V / 10A = 24 ohms |
Power Calculations
Power (watts) is calculated as: P = V x I (for DC and purely resistive AC circuits).
For AC circuits with motors and other inductive loads:
- Apparent power (VA) = V x I
- True power (W) = V x I x power factor
- Power factor = true power / apparent power
Exam Math
The Red Seal exam tests Ohm's Law calculations directly. Practice V = IR, I = V/R, and R = V/I until they are automatic. Also know P = V x I for power calculations.
Series vs. Parallel Circuits
- Series: components connected end-to-end. Current is the same through all. Voltage divides across components. Total resistance = R1 + R2 + R3.
- Parallel: components connected across the same voltage. Voltage is the same across all. Current divides. Total resistance is less than the smallest individual resistance.
Ohm's Law (V = IR) is the foundation of all HVAC electrical calculations. In series circuits, current is the same and voltage divides. In parallel circuits, voltage is the same and current divides. Power = voltage times current.