Drawings and Diagrams for Electrical, Instrumentation, and Control During BED, DED, and Commissioning
In the execution of industrial projects—particularly in power generation, oil & gas, petrochemical, and manufacturing sectors—engineering drawings and diagrams serve as critical tools throughout every phase: from Basic Engineering Design (BED) and Detailed Engineering Design (DED) to construction and final commissioning.
This comprehensive guide explores the various types of electrical, instrumentation, and control drawings used in project lifecycles. It explains their specific roles, differences, and how each contributes to effective communication, safe implementation, and project success.
Why Drawings Matter in Engineering Projects
Drawings are the universal language of engineering. They translate design intent into actionable field work and provide clarity for cross-discipline collaboration. During BED, DED, and commissioning phases, choosing the right type of drawing ensures that:
- Engineers can communicate specifications clearly
- Technicians can implement designs correctly
- Inspectors and auditors can verify compliance
- Operations teams can safely maintain systems
Lifecycle of Engineering Drawings
| Phase | Purpose |
|---|---|
| BED (Basic Engineering Design) | Conceptual layout, block diagrams, design basis development |
| DED (Detailed Engineering Design) | Final schematics, wiring diagrams, loop diagrams, GA drawings |
| Procurement & Construction | Cable routing, termination diagrams, installation drawings |
| Commissioning & Start-Up | Test plans, redlines, as-built documentation |
Main Types of Electrical, Instrumentation, and Control Drawings
1. Single Line Diagrams (SLDs)
- Purpose: High-level overview of the electrical power distribution system
- Contents: Transformers, circuit breakers, protection devices, voltage levels
- Used In: BED and DED stages for power architecture planning
2. Wiring Diagrams
- Purpose: Detailed connections between components
- Contents: Terminal blocks, wire numbers, cable tags, interconnections
- Used In: DED, construction, and commissioning for field wiring and verification
3. Schematic or Elementary Diagrams
- Purpose: Logical function representation
- Contents: Control logic, relay contacts, PLC IOs, circuit behavior
- Used In: DED and troubleshooting during commissioning
4. Loop Diagrams
- Purpose: Complete signal path from field device to control system
- Contents: Transmitter, junction box, marshalling cabinet, DCS or PLC IO
- Used In: DED, construction, loop testing, commissioning
5. Block Diagrams
- Purpose: Simplified representation of control and communication structure
- Contents: PLCs, HMIs, SCADA, signal flow between major components
- Used In: BED, training materials, system overviews
6. Layout Drawings (GA – General Arrangement)
- Purpose: Physical placement and installation references
- Contents: Cable trays, control panels, field instruments, junction boxes
- Used In: DED, construction planning, as-built documentation
7. Cable Schedule and Termination Drawings
- Purpose: Identify cable types, routes, and termination points
- Contents: Cable tag, from-to information, termination side details
- Used In: DED, construction, QA/QC during pre-commissioning
Drawings in the Project Lifecycle: When and Why They’re Used
BED Phase:
Focus is on defining system architecture, functional overview, and design basis. Drawings include:
- Block diagrams
- Preliminary SLDs
- Conceptual layout drawings
DED Phase:
The most detailed design stage. Drawings here are critical for procurement and construction.
- Final SLDs
- Loop diagrams
- PLC IO lists
- Panel wiring schematics
- Termination details
- Hook-up drawings for instruments
Construction and Installation:
During site execution, accurate drawings ensure proper installation.
- GA layouts
- Conduit and tray layouts
- Installation and routing drawings
Commissioning Phase:
Field testing, loop checks, and start-up rely heavily on clear drawings.
- Updated loop diagrams
- Redlined wiring diagrams
- Instrument index and calibration sheets
- As-built drawings finalized post-verification
Practical Example: Commissioning of an MCC Panel
Drawings used during commissioning:
- SLD for understanding power hierarchy
- Wiring diagram for control circuit tracing
- Schematic diagram for interlock logic
- Termination drawing for verifying cable ends
Troubleshooting a control failure:
- Use loop diagram to check signal from pushbutton to PLC
- Verify IO mapping and actual field signal using wiring diagram
Common Errors and How to Avoid Them
| Error | Prevention Tip |
| Using outdated revision drawings | Implement strict document control processes |
| Incomplete loop or termination diagrams | Validate with a full IO-checklist before issuing drawings |
| Ambiguous symbols or labeling | Follow IEC/ISA standards and legends consistently |
| Drawing mismatch across disciplines | Perform drawing reviews with cross-functional teams |
Tips for Creating and Managing High-Quality Drawings
- Use standard templates and drawing numbering conventions
- Include revision history and approval workflow
- Apply recognized standards like IEC 61082, ANSI Y14, ISA-5.1
- Use CAD software such as AutoCAD Electrical, EPLAN, or SmartPlant
- Archive all drawings in centralized document control systems (e.g., EDMS)
Digital Trends: Intelligent Drawing Systems
- Smart Loop Diagrams: Integrated with asset databases and automatically updated
- BIM and 3D Modeling: Used for complex cable routing and spatial planning
- Augmented Reality: Emerging tool for overlaying digital drawings onto field equipment during commissioning
Conclusion: Drawings as the Foundation of Project Execution
From conceptualization to commissioning, the success of electrical, instrumentation, and control systems hinges on the quality and clarity of drawings. Choosing the right type—whether schematic, loop, wiring, or layout—ensures precise execution, minimizes delays, and enhances safety.
Effective drawing management and standardization across all project phases not only supports accurate implementation but also serves as a vital record for operation, maintenance, and future expansions.