Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

Which formula is used to determine wattage in an electrical circuit?

1. W = R x I

2. W = E x R

3. W = E x I

4. W = I x R

The correct answer is: W = E x I

To determine wattage in an electrical circuit, the correct formula is W = E x I, where W represents power in watts, E is voltage in volts, and I is current in amperes. This relationship comes from the fundamental power equation that illustrates how electrical power is generated in a circuit. When voltage is applied across a circuit and current flows, the product of these two quantities results in the power consumed or produced by the circuit. In practical terms, if you know the voltage supplied to a circuit and the current flowing through it, you can easily calculate the power usage or generation, which is critical in the sizing and evaluation of electrical components in HVAC systems. Understanding this formula is crucial, especially in HVAC applications where different components (like motors, compressors, and electrical resistance heaters) operate based on specific voltage and current ratings. Each element's power requirements will determine circuit sizing, load calculations, and overall energy efficiency assessments. The other formulas provided, such as W = R x I or variations involving resistance, do not accurately represent the relationship needed to directly calculate wattage in an electrical circuit under standard conditions. They may be applicable in specific contexts such as Ohm's law and calculating voltage, but they do not serve as general power equations.