Understanding Electrical Panel Design — Step by Step

An electrical panel — whether a Motor Control Centre, a PLC control cabinet, or a distribution board — is the physical heart of any electrical system. Every machine that moves, every process that runs, every motor that starts does so because an engineer designed the panel that controls it correctly.

Getting panel design wrong does not just mean a rework — it means commissioning delays, client complaints, and in safety-critical applications, real risk to people and equipment.

This guide walks through the complete panel design process, from the first requirements question to the final FAT sign-off, using the workflow we follow at Vidhasri Technology on every project.

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Step 1 — Understand the Requirements Before Opening Any Tool

The problem: The single most expensive mistake in panel design is starting the schematic before the requirements are fully understood. Every assumption that turns out to be wrong means redrawing.

Questions that must be answered before design begins:

• What is the supply voltage and number of phases? (e.g., 400V 3-phase 50Hz)
• What loads will the panel control? (motors, heaters, lighting, instruments)
• What is the prospective fault level (Isc) at the installation point?
• Which standards apply? (IEC 60204-1, NFPA 79, local authority requirements)
• What enclosure IP or NEMA rating is required?
• What is the ambient temperature at the installation site?
• Are there functional safety requirements? (SIL level, safety category per ISO 13849)

The benchmark: Before a single symbol is placed in EPLAN, every question above should have a documented, client-confirmed answer. Any open question is a rework waiting to happen.

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Step 2 — Create the Single Line Diagram First

The problem: Engineers who start with detailed control circuit design before agreeing on the power architecture waste significant time when the protection hierarchy changes — which it almost always does when reviewed.

What the SLD establishes:

• Incoming supply → main circuit breaker or isolator
• Main busbar → branch feeder circuit breakers
• Branch feeders → loads (motors, sub-panels, UPS, instruments)

The SLD shows the power distribution topology and protection hierarchy — the architecture the entire project is built on. It is not the detailed wiring diagram.

The benchmark: The SLD should be reviewed and approved before detailed schematic design begins. Changes at SLD stage cost hours. Changes at detailed schematic stage cost days.

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Step 3 — Select Components Based on Calculations

The problem: Component selection based on approximation or “what we used last time” produces panels that fail FAT or generate field failures. Every component must be sized against calculated requirements.

For circuit breakers and contactors:

• Calculate full-load current: I = P / (√3 × V × cosφ) for 3-phase motors
• Apply 125% factor for continuous loads (IEC 60204-1 requirement)
• Check breaking capacity against prospective fault level (Isc)
• Confirm selectivity between upstream and downstream breakers

For cables:

• Size by current-carrying capacity and acceptable voltage drop
• Apply derating factors for ambient temperature and bundling (IEC 60364-5-52)

For enclosures:

• Calculate total heat dissipation (sum of all component losses)
• Verify whether forced cooling is required

The benchmark: All component selections should be traceable to a calculation. Engineering judgment is not a calculation — it is a risk.

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Step 4 — Design the Schematic in EPLAN

The problem: Engineers who start drawing without configuring EPLAN correctly produce schematics that generate hundreds of project check errors and unusable documentation.

The correct EPLAN setup before drawing begins:

• Configure IEC 81346 reference designation schema for this project
• Set automatic wire numbering from the correct starting potential
• Link all selected components to verified parts database entries
• Set up page templates for each circuit type

Schematic structure:

• Power pages: Incoming supply → busbar → individual motor/load feeders
• Control pages (24VDC): PLC I/O wiring — sensors to inputs, outputs to coils
• Safety pages: E-Stop circuit, safety relay connections, door interlocks
• Terminal pages: Auto-generated by EPLAN from the schematic data

Key practices:

• Use IEC 81346 reference designations consistently from the first page
• Let EPLAN assign wire numbers automatically — never number manually
• Use page macros for repeated circuits

The benchmark: An EPLAN project check before design review should produce zero errors related to wire numbering, cross-references, open connections, or missing article numbers.

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Step 5 — Generate Documentation Automatically

The problem: Teams that generate documentation manually after completing the schematic spend days on work that EPLAN does in minutes — and introduce errors that the schematic does not contain.

What EPLAN generates automatically:

• Bill of Materials — every placed device with article number, quantity, and manufacturer
• Terminal strip diagrams — every terminal with internal and external connections
• Cable overview — every cable with source, destination, and cross-section
• Connection list — every wire with start and end device references

The benchmark: Complete project documentation should be generated and reviewed in under 30 minutes for a typical project.

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Step 6 — Design Review Before Release

The problem: Design reviews that focus on basic documentation errors waste senior engineering time on things EPLAN’s project check should catch automatically.

What the review should cover:

• Protection coordination — verify selectivity between all upstream and downstream breakers
• Safety circuit review — E-Stop meets the required Performance Level (PL) or SIL rating
• Customer-specific requirements — deviations from standard are explicitly documented
• EPLAN ERC pass — zero errors before manual review begins

The benchmark: Manual review should focus exclusively on engineering intent and functional correctness — not on documentation completeness.

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Step 7 — Factory Acceptance Test

The problem: FAT failures that could have been caught in design review cost the most — the panel is built, the client is present, and a deficiency means delay, rework, and a damaged relationship.

The FAT protocol:

• Visual inspection — physical build matches the schematic
• Insulation resistance test — megger test on all power cables before energising
• Functional test — every contactor, input, and output operated against the schematic
• Safety circuit test — E-Stop response, reset sequence, and safety relay logic verified
• FAT sign-off — client witnesses and signs the FAT protocol

The EPLAN schematic is the reference document throughout the entire FAT procedure.

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How Vidhasri Technology Delivers Panel Design Projects

At Vidhasri Technology, we design complete electrical panels in EPLAN Electric P8 — from the first requirements question to manufacturing-ready drawings.

Our panel design services include:

1. Full Schematic Design — Power, motor control, PLC I/O, safety circuits in IEC 81346-compliant EPLAN
2. Automated Documentation — BOM, terminal diagrams, cable schedules from the design data
3. EPLAN Pro Panel 3D Layout — Physical panel layout for enclosure sizing and cable routing
4. Standards Compliance Review — IEC 60204-1, customer requirements, and EPLAN project check
5. FAT Support Documentation — Complete test protocol linked to the approved schematic

Contact us to discuss your panel design project — no commitment, just a conversation.

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A Real-World Illustration

One of our clients — a UAE-based machine builder — was experiencing consistent commissioning delays because terminal plan errors were only discovered on site. Field engineers were manually cross-checking the schematic against the physical panel during commissioning — a process adding 1–2 days per machine.

After migrating their design workflow to EPLAN with automatic terminal plan generation, those discrepancies disappeared. The terminal plans were accurate by construction — generated from the same data as the schematic, with zero manual transcription.

The same design engineers. A different tool. Zero terminal errors on commissioning.

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Is Your Panel Design Process Ready for the Next Project?

Start with a free 30-minute consultation. We will review your current panel design workflow and tell you exactly where EPLAN automation can reduce engineering time and eliminate your most common rework triggers.

Contact Vidhasri Technology — and design your next panel correctly, the first time.

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Summary: The Panel Design Process

Step	What You Do	What Goes Wrong Without It
1	Confirm all requirements before design	Assumptions become reworks
2	Create and approve the SLD first	Architecture changes late in design
3	Select components from calculations	Components fail FAT or field service
4	Design schematic in EPLAN correctly	Project check failures, unusable documentation
5	Generate documentation automatically	Hours of manual work, errors in BOM and terminal plans
6	Run ERC then design review	Senior engineers waste time on basic errors
7	FAT against the approved schematic	Site commissioning reveals design deficiencies