Which elements belong on the SLD?
The project drawing standard controls symbols and annotation. The drawing should keep the primary path readable while preserving the identifiers needed to cross-reference equipment, schedules and schematics.
| Layer | Show | Review question |
|---|---|---|
| Sources | Utility, generators or incoming feeders | Is the boundary clear? |
| Primary equipment | Transformers, buses and switchgear | Do tags match schedules? |
| Protection | CTs, VTs, relays and trip references | Is the protection intent supplied? |
| Outgoing circuits | Feeder tags and destinations | Can each load be traced? |
| Notes | Ratings, states and open items | Which facts still need approval? |
Which standards help frame the drawing?
IEEE C2 covers practical safeguarding for electric supply stations and supply lines in the United States. IEC 61936-1 covers design and erection requirements for power installations above 1 kV AC within its stated scope. IEC 60617 is the official IEC source for electrotechnical diagram symbols. Apply the standards and editions named by the project and jurisdiction.
Sources: IEEE Standards Association: IEEE C2-2023 National Electrical Safety Code, International Electrotechnical Commission: IEC 61936-1:2021, International Electrotechnical Commission: IEC 60617 Graphical Symbols for Diagrams
What does the drafting review check?
A drafting review checks tags, symbols, cross-references, line continuity, revision notes and drawing readability. Engineering sign-off is performed only by the registered engineer responsible for the job.
- No unreferenced equipment tag
- No hidden break in the power path
- Open design inputs marked for review
- Revision changes recorded
Common questions
What else should the bid team know?
Is a one-line diagram the same as a single line diagram?
Yes. One-line diagram is common US wording for the same drawing type.
Does an SLD show every control wire?
No. Detailed control, trip and indication circuits belong in schematics and related schedules.
Who approves the SLD?
The registered engineer responsible for the project performs engineering sign-off. A drafter can prepare and check the drawing.
Primary sources
- IEEE C2-2023 National Electrical Safety CodeIEEE Standards Association
- IEC 61936-1:2021International Electrotechnical Commission
- IEC 60617 Graphical Symbols for DiagramsInternational Electrotechnical Commission
- 29 CFR 1910.269Occupational Safety and Health Administration