What is a Single Line Diagram?
A Single Line Diagram, SLD (also called one-line diagram), is a simplified electrical schematic that represents a power system using single lines and standard symbols. The "single line" name refers to the convention of drawing each three-phase or multi-conductor circuit as one line, with standard symbols (IEC 60617) indicating equipment type.
For solar projects, the SLD shows the electrical topology from array to grid: solar modules organised into strings with kWp, Voc, and Isc noted; combiner boxes aggregating strings; DC disconnects between combiner and inverter; the inverter itself with its specifications; AC disconnects between inverter and meter; energy and net meters; and the connection point to the DISCOM grid or local load.
The SLD does not show physical panel layout or actual cable routing. Those go in separate site layout drawings and wiring diagrams. SLD is the high-level electrical topology view that regulators, design reviewers, O&M teams, and emergency responders use to understand the system.
Why SLD matters
For regulatory compliance, the SLD is a mandatory submission. DISCOM net metering applications require SLD review; CEI sanction for projects above threshold capacity requires SLD evaluation. Quality EPC practice produces SLDs that pass first review without revisions.
For project handover and operations, the SLD is the reference document. When O&M teams troubleshoot, they consult the SLD to understand topology. When new technicians arrive, the SLD orients them. As-built SLDs (updated to reflect actual installed configuration) are essential for long-term operations.
For project finance, SLDs are part of lender due diligence packages. Quality SLDs signal engineering rigour and reduce technical due diligence findings.
How a solar SLD is created
- Design completion. kWp, modules, inverter, configuration.
- Topology decisions. String count, combiner placement.
- Equipment selection. Specifications locked.
- Symbol selection. IEC 60617 standard.
- Drawing creation. AutoCAD, EPLAN, Visio, draw.io.
- Protection elements. Disconnects, fuses, SPDs.
- Earthing and grounding. Shown clearly.
- Title block. Project, date, revision, engineer.
- Engineer signature. Qualified review.
- DISCOM and CEI submission. As required.
Benefits of disciplined SLD practice
- Regulatory clearance. First-pass DISCOM and CEI approval.
- Operational reference. O&M team understanding.
- Emergency safety. First responder reference.
- Project finance support. Lender due diligence.
- Customer documentation. Quality handover.
- Audit trail. As-built configuration record.
- Insurance acceptability. Documented installation.
Limitations and challenges
Time-consuming for small EPCs. Manual SLD effort.
Software cost. Professional CAD licensing.
Standard variation. DISCOM-specific formats.
Drift from as-built. SLD not updated during execution.
Engineer scarcity. Quality electrical engineers in demand.
SLD requirements across Indian solar segments
| Project type | SLD requirements |
|---|---|
| Residential rooftop (under 10 kW) | Simple SLD for DISCOM net metering |
| Residential premium (10 to 25 kW) | Detailed SLD with CEI consideration |
| Commercial rooftop (up to 1 MW) | Engineer-signed SLD, DISCOM + CEI |
| Industrial captive (1 MW+) | Full SLD with HT connection details |
| SECI utility-scale tender | Comprehensive bid SLD |
| PM Surya Ghar residential | Standardised SLD per portal flow |
Quick facts
| Full form | Single Line Diagram |
|---|---|
| Purpose | Simplified electrical topology view |
| Standard | IEC 60617 symbols |
| Required for | DISCOM net metering, CEI sanction |
| Software | AutoCAD Electrical, EPLAN, Visio, draw.io |
| Includes | Array, combiner, disconnects, inverter, meters |
| Excludes | Physical layout, cable routing |
Common mistakes about SLD
- Non-standard symbols. DISCOM rejection.
- Missing protection elements. Safety review fails.
- No engineer signature. CEI sanction blocked.
- Outdated SLD post-changes. Audit and dispute risk.
- Confusing SLD with layout. Wrong document submitted.
- No earthing shown. Safety review fails.
- Incomplete title block. Rejected on technicality.
- Skipping DISCOM-specific format. Rework required.
Key takeaways
- SLD is simplified electrical schematic using IEC symbols.
- Required for DISCOM net metering and CEI sanction.
- Shows array, combiner, disconnects, inverter, meters.
- Does not show physical layout or cable routing.
- Engineer-signed for regulatory submissions.
- As-built SLD reflects actual installation.
- Reference for operations, safety, due diligence.
Frequently Asked Questions
What is a Single Line Diagram?
A Single Line Diagram (SLD) is a simplified electrical schematic representing the components of a power system using single lines and standard symbols. For solar projects, the SLD shows the array, combiner boxes, DC disconnect, inverter, AC disconnect, meter, and grid connection point. SLDs are required for DISCOM net metering applications and CEI safety approvals.
Why is the SLD required?
For regulatory approval, electrical safety review, project documentation, and operational reference. DISCOM net metering applications require SLD submission. CEI sanction for projects above threshold capacity requires SLD review. Quality EPCs include SLD in project handover documentation.
What goes in a solar SLD?
Solar array (number of strings, modules per string, voltage, current), combiner box, DC disconnect, inverter, AC disconnect, AC and DC fuses, earthing, lightning protection, energy meter, net meter, and connection to grid or load. Standard symbols (IEC 60617) are used.
Who draws the SLD?
The EPC's design engineer typically. For larger projects, dedicated electrical engineers or consulting firms may be engaged. SLD must comply with IEC and BIS standards and reflect actual installed equipment.
What software is used for SLD?
AutoCAD Electrical, EPLAN, SEE Electrical for engineering teams. For SMB EPCs, generic drawing tools (Visio, draw.io) or solar-specific tools (PVsyst, HelioScope export) suffice. Quality SLDs follow standard symbols and naming conventions.
Is the SLD same for residential and commercial?
Same concept, different complexity. Residential SLD is simpler (one inverter, one string or two, basic protection). Commercial SLD shows multiple strings, multi-inverter configuration, three-phase distribution, more protection elements.
How is SLD different from the wiring diagram?
SLD uses single lines and simplified symbols to show overall topology. Wiring diagram shows actual cable runs, terminal connections, and physical wiring details. SLD is for high-level understanding; wiring diagram is for installation execution.
Does the SLD show panel layout?
No. SLD is electrical topology, not physical layout. Panel layout is shown in a separate site plan or layout drawing. The two complement each other.
What standards apply to SLD?
IEC 60617 for electrical symbols; IEC 60364 for installation safety. Indian context: CEA Technical Standards for Connectivity, BIS IS/IEC 60947 for switchgear. DISCOM-specific formats may apply.
Is the SLD updated during execution?
Yes when design changes happen. Field substitutions, scope changes, and approved variations should be reflected in revised SLD. As-built SLD documents actual installed configuration.
Does the SLD need to be signed and stamped?
Often yes for regulatory submissions. CEI sanction requires registered electrical engineer signature. DISCOM net metering may require similar. Quality EPC SLDs are signed by qualified engineers.
Can the SLD be in a specific format?
DISCOMs may specify format requirements: title block content, symbol style, paper size. Quality EPCs maintain templates aligned to DISCOM expectations for each state served.
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- IEC 60617. Graphical symbols for diagrams.
- IEC 60364. Electrical installations.
- CEA Technical Standards for Connectivity. Grid connection requirements. cea.nic.in
- BIS IS/IEC 60947. Low-voltage switchgear standards.
- State DISCOM net metering documentation.
- MNRE technical guidelines. mnre.gov.in
- Solar EPC design practices. Industry SLD templates.
Written by QuickEstimate Editorial, QuickEstimate Editorial (Surat).
Last updated: 4 June 2026.