How to Read an Electrical Schematic Diagram
Learn how to read electrical schematic diagrams step by step — covering symbols, wire numbers, reference designations, cross-references, and how EPLAN makes large schematics easier to navigate.
How to Read an Electrical Schematic Diagram
Every electrical engineer, technician, and automation professional works with schematics daily — yet many beginners find them intimidating at first glance.
A schematic is not a photograph of a panel. It is a structured language with its own grammar, symbols, and rules. Once you learn that language, you can troubleshoot faults, verify designs, commission machines, and understand equipment behaviour — all without touching a single wire.
The good news: there are only six things you need to understand to read any professional schematic. This guide walks you through each one.
Step 1 — Identify the Standard the Schematic Follows
The problem: IEC and NFPA 79 schematics look completely different — different symbols, different wire colours, different reference designations. If you try to read an IEC schematic using NFPA knowledge, you will misread it.
What to look for:
- IEC (IEC 60617 / IEC 81346) — Used in Europe, Asia, Middle East, Australia. Functional reference designations with
=,+,-prefixes. Used in EPLAN Electric P8 by default. - NFPA 79 / ANSI/IEEE — Used in USA and Canada. Simpler alphanumeric tags. Ladder diagram format common.
The benchmark: Before reading any schematic, confirm the standard. It is usually stated in the title block or project notes.
| Standard | Region | Key Feature |
|---|---|---|
| IEC 60617 / IEC 81346 | Europe, Asia, Middle East | Functional reference designations (=, +, -) |
| NFPA 79 / IEEE | USA, Canada | Ladder diagrams, component-based references |
Step 2 — Learn the Core Symbols
The problem: Engineers who have not memorised standard symbols spend valuable time on every new schematic decoding what each element represents instead of understanding the circuit logic.
The most common symbols you will encounter:
| Symbol | Component |
|---|---|
| Horizontal lines | Live conductors (L1, L2, L3) |
| Box with coil | Contactor or relay coil |
| Open gap contact | Normally Open (NO) contact |
| Diagonal line contact | Normally Closed (NC) contact |
| Circle with X | Motor |
| Triangle or box | Fuse or circuit breaker |
| Rectangle with terminals | PLC module or relay |
What this means for your practice: Download the IEC 60617 symbol reference sheet and keep it open while reading new schematics. Within a few weeks of regular use, you will recognise symbols without looking them up.
Step 3 — Understand the Page Layout
The problem: Beginners scan a schematic randomly, jumping between pages without understanding the logical flow. This wastes time and causes missed connections.
How professional schematics are structured:
- Top of the page: Power rails (L1, L2, L3, PE, 24VDC)
- Left side: Input signals — sensors, pushbuttons, field devices
- Right side: Output loads — contactor coils, solenoid valves, indicators
- Bottom: Wire numbers, cross-references, page zones
Each page typically covers one circuit function — Page 1 = Main Power Distribution, Page 2 = Motor Control, Page 3 = PLC Digital I/O.
The benchmark: In a well-structured EPLAN project, you should be able to find any specific circuit function within 30 seconds by reading the page titles and structure.
Step 4 — Follow the Wire Numbers
The problem: In large projects with hundreds of pages, the same electrical potential appears on multiple pages. Engineers who do not follow wire numbers lose the thread of the circuit and make incorrect assumptions about connections.
How wire numbers work:
- Every wire has a unique number (called a potential) that identifies it across all pages
- When you see
24V_CTRLon Page 3 and Page 7, those points are physically connected PEalways connects to earth ground — it is never isolated
What this means in EPLAN: Wire numbers are tracked and cross-referenced automatically throughout the entire project. In a 500-page project, every wire number is still unique and traceable.
The benchmark: You should be able to trace any wire number from its source to its destination without leaving the schematic document.
Step 5 — Read the Reference Designations
The problem: Engineers who do not understand IEC 81346 reference designations cannot locate components in large projects, cannot read BOMs accurately, and cannot navigate between the schematic and the physical panel.
How IEC 81346 designations work:
A reference like =PANEL+DB1-Q1 breaks down as:
=PANEL→ Functional aspect (Main Panel function)+DB1→ Location aspect (Distribution Board 1)-Q1→ Product aspect (Circuit Breaker 1)
This system lets you locate any component on any page of a large project instantly — and links every component directly to the BOM.
The benchmark: Given any component reference designation, you should be able to find its page, its physical location, and its BOM entry in under 60 seconds.
Step 6 — Use Cross-References
The problem: A relay coil appears on Page 2 but its contacts are on Pages 5, 7, and 12. Engineers who miss cross-references think a circuit is incomplete when it is actually correct — just split across pages.
How cross-references work:
- When a coil appears on one page, arrows or page/column references point to every contact across the project
- In EPLAN, these are generated automatically and stay accurate when pages are added or removed
What this means for troubleshooting: Always follow cross-references before concluding that a circuit has a fault. The missing element is almost certainly referenced on another page.
How Vidhasri Technology Can Help Your Team
At Vidhasri Technology, we design and document complex electrical systems in EPLAN Electric P8 — and we train engineering teams to read, navigate, and maintain professional schematics efficiently.
Our services include:
- EPLAN Project Review — Assess your current schematics for structure, clarity, and compliance
- Team Training — Hands-on sessions on IEC 81346, EPLAN navigation, and schematic reading
- Documentation Standards — Build internal standards that make your schematics readable by any engineer
- Schematic Development — Full electrical design from specification to manufacturing-ready drawings
Contact us to discuss your schematic design needs — no commitment, just a conversation.
A Real-World Illustration
One of our clients — a UAE-based panel builder — had commissioning engineers spending 3–4 hours per panel navigating schematics to understand the circuit logic. After a half-day training session on IEC 81346 reference designations and EPLAN cross-reference navigation, that dropped to under 45 minutes.
The same schematics. The same engineers. A different understanding of the language.
Is Your Team Ready to Read Schematics Confidently?
Start with a free 30-minute consultation. We will review your team’s current schematic reading challenges and tell you exactly what training or documentation would solve them.
Contact Vidhasri Technology — and start reading schematics the way they were meant to be read.
Summary: The 6 Steps to Reading Any Electrical Schematic
| Step | What You Learn | Why It Matters |
|---|---|---|
| 1 | Identify the standard (IEC or NFPA) | Symbols and references are completely different between standards |
| 2 | Learn core symbols | Instant symbol recognition speeds up all schematic reading |
| 3 | Understand page layout | Navigate to the right circuit without random searching |
| 4 | Follow wire numbers | Trace connections across all pages of a large project |
| 5 | Read reference designations | Locate any component instantly in a large project |
| 6 | Use cross-references | Find coils, contacts and related circuits wherever they appear |