Hello everyone, I am Lao Liu, and I have been in the electrical automation industry for over 20 years. Today, I want to talk to you about PLC electrical CAD drawing.
I remember when I first started, an experienced engineer told me: “Xiao Liu, as an engineer, your drawings are your face!” This is absolutely true. I have seen too many times when a technician hands over a messy drawing, and the client’s face immediately drops.
Below, I will share the top ten standards for electrical CAD drawing that I have developed over the years. Follow these guidelines, and your drawings will definitely look “professional!”
1. Frame Setup: Establish Rules First
The frame is the “face” of the entire set of drawings and must be standardized.
Practical Tips:
- Use a unified A3 frame (420×297mm) for easy printing and binding.
- The frame should include project name, design date, version number, designer/reviewer information, etc.
- Each drawing must have a unique number, e.g., E-PLC-001 (Electrical-PLC Control-Page Number).
Last month, I visited a client and saw that their drawings didn’t even have a frame, just a bunch of lines. After searching for a long time, I couldn’t tell who drew it or when it was drawn. In such cases, who is responsible if something goes wrong?
2. Layer Management: Internal Hierarchy
Many beginners throw all content onto one layer, which is a big taboo!
Standard Practice:
- Power Line Layer: POWER
- Control Line Layer: CONTROL
- PLC I/O Wiring Layer: PLC
- Text Annotation Layer: TEXT
- Frame Layer: BORDER
// Layer Naming Example
POWER - Color Red - Line Width 0.5mm
CONTROL - Color Blue - Line Width 0.35mm
PLC - Color Green - Line Width 0.35mm
TEXT - Color Black - Line Width 0.18mm
BORDER - Color Black - Line Width 0.7mm
Last year, I helped a factory modify their drawings, and all content was on one layer. I couldn’t even modify the control circuit separately. In the end, the entire drawing had to be redrawn, wasting more than half a day.
3. Line Type Standards: Thickness Matters
The line types in electrical drawings must follow these rules:
- Main Circuit: Thick Solid Line (0.5mm)
- Control Circuit: Medium Solid Line (0.35mm)
- Virtual Connection: Dashed Line (0.25mm)
- Ground Wire: Special Ground Symbol Line (0.5mm)
I have seen many novice engineers use the same thickness for all lines, making it difficult to distinguish between the main circuit and control circuit. Remember: Line type standards are not for aesthetics; they are to help people quickly identify circuit functions!
4. Component Symbols: National Standards First
Component symbols must comply with the national standard GB/T 4728 series.
Common Mistakes:
- Using a rectangular box to replace relay contacts.
- Drawing contactor coils as resistor symbols.
- Randomly drawing PLC input/output points.
// Correct Component Symbol Examples
Relay Normally Open Contact: -| |-
Relay Normally Closed Contact: -|/|-
PLC Input Point: ----[ ]----
PLC Output Point: -----( )-----
Once, I visited a company and saw that their three-phase motor symbol was drawn as three circles. I was stunned. If this were handed to a foreign client, they would definitely think you are unprofessional.
5. Numbering System: Traceable
Every component on the drawing must have a unique number for easy lookup and maintenance.
Standard Numbering Method:
- Breaker: QF1, QF2…
- Contactor: KM1, KM2…
- Relay: KA1, KA2…
- Button Switch: SB1, SB2…
- PLC Input Point: X0.0, X0.1…
- PLC Output Point: Y0.0, Y0.1…
Last year, on a project for a water plant, the client reported that a solenoid valve was not functioning. Thanks to the standardized numbering on the drawings, I quickly located the corresponding solenoid valve and wiring position through the number Y2.3, and resolved it in 10 minutes! If the numbering were chaotic, it could take several hours to troubleshoot.
6. Terminal Blocks: Clear Portals
Terminal blocks are the “portals” of the electrical cabinet and must be drawn clearly.
Standard Points:
- Terminal blocks must have clear numbering: X1, X2…
- Each terminal must indicate the wiring sequence: 1, 2, 3…
- External devices must be labeled with name and model.
Terminal block diagrams are best placed on a separate page at the front of the drawings for easy installation and inspection.
A new engineer once drew the terminal blocks with just a few lines, and when the electricians went to install, they complained to me: “How do we read this drawing?”
7. Cross-Referencing: Connecting the Dots
In large control system drawings, there are often cross-page connections that must be properly cross-referenced.
Standard Practice:
When a circuit continues from one page to another:
On the first page, indicate the source: →E-PLC-003/5 (indicating it leads to line 5 on page 3)
On the third page, indicate the reference: ←E-PLC-001/12 (indicating it comes from line 12 on page 1)
Last month, on a chemical plant project with over 700 I/O points and more than 50 pages of drawings, we were able to quickly locate each signal circuit thanks to standardized cross-referencing.
8. Modification Records: Leave a Trace
Modifications to drawings must be recorded. A professional practice is to set up a modification record table within the frame:
| Version | Date | Modification Content | Modifier |
|-----|-----------|----------------|-------|
| A | 2023/01/15| First Release | Lao Liu |
| B | 2023/03/02| Added Safety Circuit | Lao Liu |
A former client I worked with always kept records of modifications. After five years, just by looking at the modification records, I could understand the entire system’s evolution history, making maintenance much easier.
9. PLC I/O Table: Clear at a Glance
PLC drawings must include a complete I/O table, containing:
Essential Content:
- I/O Address
- Signal Type (DI/DO/AI/AO)
- Device Name
- Terminal Number
- Function Description
| Address | Type | Device Name | Terminal Number | Function Description |
|------|-----|--------------|-------|---------------|
| X0.0 | DI | Start Button | X1:5 | System Start |
| X0.1 | DI | Emergency Stop Button | X1:6 | Emergency Stop |
| Y0.0 | DO | Main Pump Motor | Y1:1 | Main Pump Start Control |
This table may seem simple, but it is the “bible” for on-site debugging and maintenance. Every time I bring a newcomer, I have them start by learning from the I/O table.
10. File Naming: Establish Rules
Finally, one often overlooked point is that CAD file naming must also be standardized!
Standard Naming Format:
Project_Name_Drawing_Type_Version.dwg
For example:
Paper_Machine_PLC_Control_V2.1.dwg
Don’t underestimate this point. I once took over a project where the previous engineer named all the CAD files “1.dwg”, “2.dwg”, “New.dwg”; finding materials was a nightmare!
Conclusion
These ten standards may seem simple, but if implemented properly, they will definitely give your drawings a “professional look.” Remember this phrase: Standards are not constraints; they are guarantees of efficiency..
In our department, new engineers must first pass the “drawing test,” and the standard is these ten points. A set of standardized drawings not only reflects technical strength but also serves as your professional quality card!
If you have any questions, feel free to leave a comment for discussion!