Why a single-line diagram is worth drawing properly
A single-line diagram, or SLD, shows an electrical installation as a set of single lines instead of every individual conductor. One line stands in for a three-phase run, so the drawing stays readable while still showing where power enters, how it is split, and what protects each branch. It is the first document an electrician, inspector or maintenance engineer reaches for.
A good SLD is not decoration. It is the reference that ties the incoming supply, the protective devices, the outgoing circuits and their loads into one coherent story. Get it right and the panel schedule, the cable schedule and the handover pack all follow from the same source.
Drawing the diagram online rather than on paper means it can be edited, versioned and exported at any time. Working in a browser-based CAD tool with a single shared model keeps the schematic and the calculations behind it in step, instead of letting a spreadsheet drift away from the drawing.
What to prepare before you open the editor
Time spent gathering data first saves rework later. An SLD is only as accurate as the information behind it, so collect the following before you start placing symbols:
- Supply details: nominal voltage, number of phases, frequency and the earthing system.
- The main protective device: type and rating, plus any upstream device that feeds the board.
- A list of outgoing circuits with their loads, cable sizes and protective device types.
- Any metering, surge protection or control equipment that has to appear on the diagram.
- The reference standard for the project, so the symbols and rules match from the outset.
GorkyCAD Pro supports the IEC, IS, ANSI and BS reference frameworks, and it carries 70+ calculations and IEC 60364 checks in the same model. That means the diagram you draw can be backed by the numbers that justify it, without moving between tools.
Step 1: set up the sheet and title block
Start with the frame, not the electrical content. A tidy sheet is easier to read and easier to revise later.
Choose the sheet and orientation
Pick a paper size that fits the depth of the distribution you are drawing. A domestic consumer unit fits comfortably on a small landscape sheet, while a multi-board distribution may need a larger size or a deliberate split across sheets. Landscape orientation usually suits the horizontal flow from supply to loads.
Fill in the title block
Add the project name, drawing number, revision, date and your name. A revision column sounds bureaucratic until the second issue of a drawing needs to be traced back, and at that moment it is the only thing that keeps the site working from the right sheet.
Set the drawing grid
Turn on a grid and alignment guides. Consistent spacing between branches makes the finished diagram look deliberate and, more importantly, makes a missing device obvious at a glance.
Step 2: draw the incoming supply and main device
Work from the source outwards. Everything downstream depends on how the supply is represented, so build it before the branches.
- Place the supply source, showing voltage, phases and frequency.
- Add the main switch or main protective device with its rating.
- Draw the busbar as a single heavy line from which circuits will branch.
- Show metering or surge protection where the project requires them.
- Mark the earthing arrangement so the protective path is explicit.
Keeping the supply block standard across projects pays off, because readers already know where to look. Resist the urge to invent a private symbol; use the convention of the governing standard so the diagram travels between teams without a translation.
Step 3: add the outgoing circuits and number them
With the busbar in place, branch outwards one circuit at a time. Give each branch the same building blocks so the whole diagram reads as a repeating pattern.
| Element | What it represents | Typical text |
|---|---|---|
| Circuit line | One outgoing way | F3 Lighting |
| Protective device | Overcurrent protection for the way | 10 A MCB, curve B |
| RCD group | Circuits sharing an earth-leakage device | RCD 30 mA |
| Load | The final equipment supplied | Kitchen sockets |
| Spare way | Provision for future use | Spare |
Number and name every way, and keep the same naming you will use in the panel schedule. A spare way should read Spare rather than being left blank, so nobody mistakes it for a completed circuit. In GorkyCAD Pro the schematic, the layout, the panel schedule and the cable schedule all come from this one model, so naming done here propagates to every output.
Step 4: cross-check and annotate
A diagram that has never been checked is a draft, not a deliverable. Run through the drawing against the source data before you export.
- Every outgoing circuit on the list appears on the diagram, and nothing extra appears.
- Protective device ratings match the cable sizes they protect.
- RCD groups cover the circuits they are meant to cover.
- Labels are spelled consistently and follow the naming scheme.
- Loads, cable references and device types are complete enough to order materials.
Because the calculations live alongside the drawing in GorkyCAD Pro, a mismatch between a device rating and its cable can be caught while the diagram is still on screen, rather than after the board is built.
Exporting the finished diagram
An SLD is usually needed in more than one form. A PDF is the natural format for issuing a drawing, while a DXF is what other CAD tools expect when the sheet has to be shared or edited outside the original system. A drawing exported as both can be read on site and reworked by a colleague without losing the geometry.
When the diagram sits inside a wider project, it does not travel alone. GorkyCAD Pro exports to PDF, DXF, XLSX, IFC, BCF and GLTF, and it can assemble a PDF pack containing the specification, the cable schedule, the estimate and the panel passport. The same model that produced the schematic produces those documents, so there is no manual re-typing between them.
Working in the browser also means the file is reachable from site. The app runs offline as a PWA, so a diagram can be opened and reviewed where the work is, not only back at the desk.
Common mistakes to avoid
Most poor single-line diagrams fail for the same few reasons. Naming a way by its position instead of its purpose makes the drawing age badly. Leaving spares unmarked invites confusion during maintenance. Drawing three lines where one would do defeats the point of an SLD. And treating the diagram as a separate document from the schedules guarantees that the set will disagree with itself.
Avoiding those traps is mostly a matter of discipline: one naming scheme, one source of truth, and a check against the input data before export. Once the diagram lives in a browser-based CAD tool that also holds the calculations and the schedules, that discipline is built into the workflow rather than bolted on.
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FAQ
Do I need CAD experience to draw a single-line diagram online?
No. Placing symbols, branching circuits and exporting a sheet follow the same logic as the drawing itself. A browser-based tool removes most of the setup that classic CAD demands.
Can I export a single-line diagram as DXF?
Yes. GorkyCAD Pro exports to DXF as well as PDF, so a diagram can be shared for viewing or reworked in other CAD software.
Should spare ways be shown on the diagram?
Yes. Mark them clearly as spare rather than leaving them blank, so a reader can tell an unused way from a missing one.
Why keep the schematic and the schedules in one model?
Because one model means one source of truth. Names, device ratings and cable data stay consistent between the diagram and the outputs generated from it.