1. What to Read on a System Diagram (4 Categories of Information)
| Information | What to Look For |
|---|---|
| Topology | Incoming line → main breaker → busbar → outgoing line connections |
| Parameter | Model, setting current, transformation ratio, current-carrying capacity |
| Protection | Ground fault protection parameters, SPD surge protection |
| Measurement | Current transformers, meter configuration |
2. 32 High-Frequency Symbols Quick Reference (per GB/T 6988)
| Symbol | Meaning | Symbol | Meaning |
|---|---|---|---|
| QS | Isolation | QF | Circuit breaking |
| KM | Contact | FU | Fuse |
| KA | Relay | KT | Time |
| TA | Current transformer | TV | Voltage transformer |
| PA | Ammeter | PV | Voltmeter |
| PJ | Electricity meter | SPD | Surge |
| WB | Busbar | PE | Grounding |
| N | Neutral | L1/L2/L3 | Phase sequence |
| SB | Pushbutton | SA | Selector switch |
| HL | Indicator light | HA | Audible alarm |
| FR | Thermal overload relay | XT | Terminal |
| M | Motor-operated | T | Transformer |
Section 3: Circuit Numbering Rules (How to Read L1-1-W1)
Circuit number = phase + circuit number + cable code. For example, L1-1-W1 means the first cable of circuit 1 on phase L1. On a system diagram, every outgoing feeder has a unique number that corresponds to the terminal block diagram and wiring diagram.
Section 4: 5-Step Diagram Reading Method (Hands-On)
- Locate theincoming feederand identify where the power comes from
- Locate themain breakerand check its model and settings
- Locate theBusbarand check its specifications and sections
- Count theoutgoing feedersand check the destination and protection of each circuit
- Check themetering and surge protectionconfiguration
Section 5: Common Diagram Reading Mistakes (3 Items)
① Reading only the topology and ignoring the parameters — failing to verify the setting current will cause protection failure; ② Ignoring the CT ratio — meter readings must be converted; ③ Confusing PE and N — they must be drawn separately on the system diagram.
FAQ FAQ
What is the hardest part of reading a system diagram?
Symbol. Memorize the 32 high-frequency symbols and you can read 90% of diagrams.
What is the pattern in circuit numbering?
Phase (L1/L2/L3) + circuit number (1/2/3) + cable code (W1/W2), numbered from left to right.
What if I can't draw a system diagram?
Draw it with EPLAN/CADe SIMU, or send us your requirements and Zhejiang Golden Unicorn will produce the drawing free of charge.
Does the system diagram need a stamp?
Drawings supplied with the cabinet mustbe signed by three people: designer / reviewer / approver, as required by the ISO 9001 system.
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