In AC phasor analysis of a parallel RLC circuit, which quantity can always be used as the universal 0° vector reference because it is common to all branches?

Introduction:
Phasor diagrams require a reference. Selecting the shared quantity simplifies analysis and reduces mistakes. In parallel networks, voltage across each branch is identical, making it the most logical and universal reference for angles and vector sums.

Given Data / Assumptions:

• Parallel RLC topology with sinusoidal steady state.
• Ideal components and a single operating frequency.
• R, L, and C are connected in parallel across the same source.

Concept / Approach:
Because the node-to-node potential is the same for every branch, choosing voltage as the 0° phasor lets us express branch currents with simple phase relations: IR is in phase with V, IL lags V by 90° (for inductive susceptance, current lags voltage), and IC leads V by 90°. The total source current is the vector sum of these branch currents relative to the shared V reference.

Step-by-Step Solution:
1) Identify the network as parallel: common voltage, different branch currents.2) Set V to 0° on the horizontal axis.3) Draw IR in phase with V, IL at −90°, IC at +90°.4) Add currents tip-to-tail to obtain the source current phasor.

Verification / Alternative check:
Attempting to use current as a universal reference fails because each branch has a different current phase. Voltage avoids this inconsistency and clarifies the diagram immediately.

Why Other Options Are Wrong:
Current and inductive current: not common across branches; phases differ.

Reactance and resistance: component properties, not phasor references; they do not define a universal phase.

Common Pitfalls:
Using series-circuit intuition (where current is common) in a parallel context, or forgetting the 90° phase relationships of L and C currents relative to voltage.

Final Answer:
voltage