Free Single Line Diagram Generator
Enter the panel configuration — HT incomer, transformer, LT incomer and outgoing feeders — and the diagram draws itself as you type. Download it as SVG for a drawing set, or PNG for a quotation. Free, with no sign-up and nothing to install: it runs entirely in your browser, and the configuration never leaves it.
Diagram
HT side
Transformer
Full load current 876 A at 415 V.
LT side
Add-ons
Outgoing feeders
4 of 20Component schedule
| Item | Detail | Qty |
|---|---|---|
| Lightning / surge arrester | 11 kV station class, at incoming termination | 1 |
| HT isolator | Load-break isolator with earth switch | 1 |
| HT breaker — VCB | 11 kV · Incoming Feeder from Substation | 1 |
| HT metering unit | CT/PT metering cubicle | 1 |
| MDM / ABT tariff meter | Utility tariff metering on CT/PT secondaries | 1 |
| Distribution transformer | 630 kVA · Dyn11 · ONAN · 11 kV/415 V · FLC 876 A | 1 |
| Transformer fittings | Buchholz relay, OTI / WTI, Neutral CT | 1 |
| LT incomer — ACB | 1000 A | 1 |
| Metering CT set | Class 0.5 metering core | 1 |
| Multifunction meter (MFM/MDM) | kW, kWh, PF, THD on incomer | 1 |
| Ammeter & voltmeter | With phase selector switches | 1 |
| Indication lamps | R / Y / B phase indication | 1 |
| Earth fault relay | ELR with core-balance CT | 1 |
| Surge protection device | Type 2 SPD on LT bus | 1 |
| Neutral link / neutral bus | Bolted link | 1 |
| MCCB — Lighting Distribution Panel | 100 A · Sub-distribution panel | 1 |
| Energy meter — Lighting Distribution Panel | kWh meter on outgoing feeder | 1 |
| MCCB — Compressor | 250 A · VFD · 110 kW | 1 |
| Energy meter — Compressor | kWh meter on outgoing feeder | 1 |
| MCCB — Cooling Tower Pump | 160 A · star-delta · 55 kW | 1 |
| MCB — Utility & Spare | 63 A · Direct outgoing | 1 |
| Earthing | Transformer neutral and LT busbar earth | 1 |
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.
What a single line diagram leaves out on purpose
The word single is doing the work. A three-phase feeder is drawn as one line, and the diagram says nothing about which phase a load sits on or how the board is balanced across them. That is deliberate: the SLD exists to show the topology of the distribution — what feeds what, through which device, at which rating — and adding three conductors to every run would bury that under detail nobody reads at this stage.
Several other things are outside its scope by convention. Control wiring, interlocks and trip circuits belong on a schematic, not here. Physical arrangement, panel dimensions and cable routes belong on a general arrangement drawing and a cable schedule. Earthing is usually shown only at the transformer star point and the main earthing terminal, with the protective conductor for each circuit left to the cable schedule.
Knowing that boundary is what makes the drawing useful. An SLD asked to carry construction detail stops being readable as a system overview, which is the one job no other drawing in the set does.
The conventions a reviewer will expect
Symbol shapes vary between standards, and the two you will meet in India are IS 12032, which follows IEC 60617, and the ANSI set that arrives with American equipment documentation. They are not interchangeable, and the most common cause of a drawing being queried is mixing them — an IEC circuit breaker symbol on the incomer and an ANSI one on a feeder in the same diagram.
Beyond symbols, a reviewer is looking for a small number of things to be present. Every device wants a rating and a unique reference. Every cable wants a size, a core count and a length. The transformer wants its rating, both voltages, its vector group and its per cent impedance, because those four values are what anyone checking the fault level will need. Power should flow top to bottom or left to right consistently, and the supply should enter at a single, obvious point.
Where a drawing is going to a utility or an electrical inspector for approval, expect the prospective fault current at the main board to be stated explicitly, along with the breaking capacity of the incoming device. Those two numbers together are what demonstrate the switchgear can clear a fault, and a drawing that omits them is usually returned before anything else on it is read.
Questions people ask
- What arrangement will this draw, and what will it not?
- 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 with a bus coupler and second source, a DG set through an interlocked changeover, and an APFC bank on the bus. It stops there deliberately. 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.
- Why does it warn that my feeder ratings add up to more than the transformer?
- Because past a point that stops looking like diversity. Feeder ratings always over-sum, since every feeder is sized for its own peak and they never peak together — a total of 1.2 times the transformer is ordinary. The warning appears past about 1.5 times, where the more likely explanations are an undersized transformer or a mistyped rating. All the checks are advisory and none of them block the drawing, because an SLD gets sketched long before the numbers are settled.
- Why is a three-phase feeder drawn as one line?
- Because the word single is doing the work. The diagram exists to show the topology of the distribution — what feeds what, through which device, at which rating — and adding three conductors to every run would bury that under detail nobody reads at this stage. It follows that the SLD says nothing about which phase a single-phase load sits on or how the board is balanced, and it is not the drawing to check that on.
- What belongs on a single line diagram and what belongs elsewhere?
- Control wiring, interlocks and trip circuits belong on a schematic. Physical arrangement, panel dimensions and cable routes belong on a general arrangement drawing and a cable schedule. Earthing is usually shown only at the transformer star point and the main earthing terminal, with each circuit's protective conductor left to the schedule. Knowing that boundary is what keeps the drawing useful — an SLD asked to carry construction detail stops being readable as a system overview, which is the one job no other drawing in the set does.
- Which symbol set should I use — IEC or ANSI?
- Either, consistently. The two you will meet in India are IS 12032, which follows IEC 60617, and the ANSI set that arrives with American equipment documentation. They are not interchangeable, and the commonest cause of a drawing being queried is mixing them — an IEC breaker symbol on the incomer and an ANSI one on a feeder in the same diagram. Beyond symbols, a reviewer wants every device to carry a rating and a unique reference, every cable a size, core count and length, and the transformer its rating, both voltages, its vector group and its per cent impedance, because those four are what anyone checking the fault level needs.
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.