In a parallel RLC circuit, the supply voltage (V_source) can always be used as the vector reference.

Here’s why:

• In a parallel circuit, all components (resistor, inductor, and capacitor) share the same voltage source. This means the voltage across each component has the same magnitude and frequency.
• When performing phasor analysis (a method for analyzing AC circuits using vectors), we represent voltage and current as phasors. A phasor is an arrow that indicates the magnitude and phase angle of a sinusoidal quantity.
• As a reference, choosing a value that is constant in both magnitude and phase is ideal. Since the supply voltage remains constant across all branches in a parallel circuit, it becomes the perfect reference point for our phasor diagram.

Here’s a breakdown of why other values wouldn’t be suitable as a reference:

• Current: The current through each component in a parallel circuit will be different due to the varying impedance of each branch (resistance, inductive reactance, and capacitive reactance).
• Resistor Voltage (VR): While the voltage across the resistor will have the same magnitude as the source voltage, its phase angle might differ depending on the circuit’s reactance values.
• Inductor Voltage (VL) and Capacitor Voltage (VC): Similar to VR, the voltages across the inductor and capacitor will have the same magnitude as the source voltage but will have different phase angles due to their reactive properties.

By using the supply voltage as the reference (0 degrees phase angle), we can easily represent the phase lags or leads of the currents and voltages in the other branches relative to the source voltage. This simplifies the phasor diagram and helps us analyze the behavior of the RLC circuit more effectively.