Free Single Line Diagram Generator

What this draws

One HT incomer, one transformer, one LT panel, and up to twenty outgoing feeders — the shape of the great majority of industrial and commercial LT installations. Optionally a bus coupler with a second source, a DG set through an interlocked changeover, and an APFC capacitor bank on the bus.

It deliberately stops there. Ring main topologies, multi-transformer stations and auto-routed layouts are a different problem, and a tool that half-does them produces drawings nobody can trust. What is here is the standard arrangement, drawn to the convention an engineer expects to read: source at the top, transformer in the middle, busbar across, feeders hanging beneath it.

Reading the diagram

The symbols follow IEC 60617 closely enough to be read by anyone who works from single line diagrams: two interlinked circles with a delta above a star for a Dyn transformer, a circle with a G for the generator, a box with a diagonal for a breaker, paired loops on the line for instrument transformers, and the three diminishing bars for earth.

The HT breaker is drawn heavier than the LT devices, and feeder devices smaller again, so the voltage level of a symbol is apparent before you read its label. Every symbol carries its rating and type beside it, and feeder names are set at an angle so a long label cannot collide with its neighbour however tight the spacing becomes.

The checks it runs

The warnings under the diagram are advisory and never block the drawing — a single line diagram gets sketched long before the numbers are settled. It flags an LT incomer rated below the transformer's full load current, an incomer more than twice it, a DG set larger than the transformer, and feeder ratings summing to more than 1.5× the transformer.

That last one deserves explaining. Feeder ratings always over-sum, because every feeder is sized for its own peak and they never peak together — that is what diversity is. A total of 1.2× the transformer is ordinary. Past about 1.5× it stops looking like diversity and starts looking like an undersized transformer or a mistyped rating, which is where the warning appears. Use the breaker sizing calculator to check individual ratings against their cables.

Next steps

• Cable sizing calculator — size each feeder cable with derating and volt drop applied. Every feeder row has a direct link.
• MCB & MCCB sizing calculator — validate the breaker ratings entered here against the cables they protect.
• Electrical point estimator — cross-check what the distribution feeders actually have to carry.
• Transformer sizing & fault level — confirm the transformer rating and the fault current the switchgear must break.

This is a simplified representation for planning purposes only. Final SLDs must be verified and stamped by a licensed electrical engineer before use in actual installation or approval submissions.