Key Points for Reading Drawings: Five Categories
Drawings for high and low voltage complete equipment comprise five core categories: system diagrams (primary main wiring), secondary schematic diagrams (control), cabinet layout drawings, terminal diagrams, and component lists.
Industry experts suggest reading them according to type: system diagrams (primary main wiring/circuit relationships), secondary schematics (control logic/protection), layout drawings (internal cabinet arrangement), terminal diagrams (wiring correspondence), and lists (component details).
The core approach is to start with the system diagram and cross-reference it with the secondary schematics and layout drawings.
Five Categories of Drawings
- System diagram (Primary): Main wiring (incoming/feeder/bus-tie), circuit relationships;
- Secondary schematic diagram: Control/protection/signaling (logic), secondary design;
- Cabinet layout drawing: Component locations/internal layout (dimensions), basis for installation;
- Terminal diagram: Terminal blocks/wiring correspondence (circuit numbers), basis for wiring;
- Component list: Component details (brand/model/quantity), configuration verification.
Key Reading Points
First, start with the system diagram.
Read the primary system diagram (circuit structure) first, then delve into the secondary diagrams.
Second, cross-reference circuits.
Compare the system diagram with the secondary diagrams (using circuit numbers) to understand the control logic.
Third, verify the layout.
Compare the layout drawing with the component list (component locations) to verify the configuration.
Fourth, confirm the version.
Check the drawing version (revision number) to ensure the latest version is used and to avoid errors.
Pitfalls to Avoid
One common pitfall is “looking only at the system diagram.”
For those unfamiliar with secondary schematics (where control logic is unclear), use them for comparative study.
Second is the issue of “outdated drawings” (obsolete configurations);
always verify the version.
Third is “discrepancies between drawings and reality”;
cross-check the drawings against the actual equipment during acceptance inspections.
Trends and Reminders
Drawings are moving toward “digitalization”: 3D design (digital twins) and CAD/PDM (electronic drawings) are enhancing efficiency.
For end-users, the recommendation is to “review all five categories of drawings, start with system schematics, and verify versions.”
Understanding the drawings ensures clear and proper equipment operation.
