H‑Infinity

The single line diagram (SLD) is the single most important drawing in any electrical system. It shows the complete electrical distribution hierarchy from incoming supply through all transformation and distribution stages to every final circuit. Accurate, up-to-date SLDs are essential for system studies, operational procedures, maintenance planning, and emergency response. Outdated or inaccurate SLDs are one of the most common causes of errors during maintenance and commissioning.

01What is SLD Development?

Developing accurate SLDs involves documenting every element of the electrical distribution system:

▸Incoming Supplies — Utility connections, backup generators, and any parallel or interconnection arrangements.
▸Transformation Stages — All transformers with ratings, impedance, vector groups, and tap settings.
▸Distribution Equipment — All switchgear, MCCs, distribution boards, with protective device ratings and settings.
▸Circuit Information — Cable sizes, lengths, protective device ratings, and load information for each circuit.

02Why Accurate SLDs Matter

Inaccurate or outdated SLDs create serious operational risks:

▸Safety Hazards — Maintenance workers relying on incorrect SLDs can inadvertently energise live circuits or select wrong protection settings.
▸Study Inaccuracies — Power flow, short circuit, and arc flash studies require accurate SLDs. Wrong data produces unreliable results.
▸Emergency Response — During outages or emergencies, operators rely on SLDs to isolate faults and restore supply quickly and safely.
▸Regulatory Compliance — Many jurisdictions require up-to-date SLDs to be available on site at all times.

03Our Approach

We develop or verify SLDs through a rigorous field verification process:

1. Site Survey

Conduct detailed site surveys to verify existing equipment, connections, ratings, and settings against available as-built drawings.

2. Data Compilation

Compile complete equipment data — ratings, impedances, protective device settings, cable information, and load data.

3. SLD Development

Develop comprehensive SLDs showing complete distribution hierarchy with all equipment data and circuit information.

4. Verification

Conduct verification sessions with client's operations team to confirm accuracy before final issue.

04Scope of SLD Services

Our SLD services cover all aspects of electrical documentation:

▸New SLD Development — Create SLDs from scratch for new facilities or systems without documentation.
▸SLD Verification — Audit and update existing SLDs to reflect current site conditions.
▸Red-Line Markups — Review contractor submittals and mark up SLDs with required corrections.
▸As-Built SLDs — Produce final as-built SLDs incorporating all site modifications and changes during construction.

05Standards & Compliance

✓IEC 60617 — Graphical Symbols

✓ISO 14687 — SLD Conventions

✓NFPA 70E — Electrical Safety

✓OSHA 1910.269 — Electrical Power Gen

06Why H-Infinity

We've surveyed and documented electrical systems for facilities across the GCC, Africa, and Asia — from simple commercial buildings to complex 400 kV transmission networks. Our site verification process ensures every SLD we deliver accurately reflects the installed system, saving our clients from the costly errors that result from relying on outdated drawings.

Single Line Diagrams (SLD)