Electrical Equations Reference

Page review information

Edition covered: Established electrical theory — no single governing standard — n/a — textbook-level theory module
Content status: Reviewed
Coverage: Training module: Electrical Equations Reference — educational treatment; verify design decisions against the governing standards.
Last reviewed: August 2026
Primary reference: The official published standard — required for final decisions

Confirm the governing edition, jurisdiction, and project-specific requirements before applying anything on this page.

Beginner Time: 10 min Type: Reference Focus: Controls / Panel Design

After this module: Quick-reference sheet for Ohm's law, power, dividers, KCL/KVL, and capacitor/inductor energy — formatted for fast lookup.

Purpose

This page is a compact reference card for the most-used relationships from the fundamentals training set.

Ohm’s law

V = I × R
I = V / R
R = V / I

Power

P = V × I
P = I² × R
P = V² / R

Series resistance

R_eq = R1 + R2 + R3 + ...

Parallel resistance

1 / R_eq = 1 / R1 + 1 / R2 + 1 / R3 + ...

For two resistors:

R_eq = (R1 × R2) / (R1 + R2)

Voltage divider

V_out = V_s × (R_x / R_total)

Current divider

I_x = I_s × (R_other / (R_x + R_other))

Kirchhoff’s laws

Sum of currents at a node = 0
Sum of voltages around a closed loop = 0

Branch current in nodal form

I = (V_a - V_b) / R

Source transformation

V_s = I_s × R
I_s = V_s / R

Thevenin and Norton relationship

V_th = I_n × R_th
I_n = V_th / R_th

Capacitor energy

E = ½ × C × V²

← Equivalent Circuit Methods ↑ Electrical Fundamentals Passive Components →

Trust Boundary — Engineering Judgment Required

This site is an independent educational reference for industrial automation standards. It paraphrases and organizes guidance in original language; it is not a substitute for the official published standards, professional engineering judgment, or legal review, and content has not been independently verified against current published editions.

Items marked Review pending await technical review against the identified edition. Items marked Planned have no reviewed source material behind them. Do not rely on this site for compliance determinations, safety-critical design decisions, or legal interpretation.