Understanding Electrical Distribution Boards And Numbering
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Distribution Box Numbering Table
Distribution boxes and electrical panels are numbered using a structured system that includes equipment type, voltage, serial number, and circuit references to ensure clarity, safety, and compliance.
Key Numbering Components
- Equipment Category Code – Two-letter code identifying the type of equipment:
- TB – Terminal/Junction Box
- SL – Streetlight
- FL – Floodlight
- LA – General lighting
- LE – Emergency light
- LS – Light switch
- Unit Number – Two-digit number (00–99) assigned to each unit within a plant or building .
- Voltage Number – Two-digit code representing voltage level:
- 01 – 115 kV and above
- 10 – 34.5 kV
- 20 – 13.8 kV secondary voltage
- Serial Number – Two-digit number starting at 01 for each piece of equipment in a category .
- Single Letter Identifier – Used when multiple identical pieces of equipment share a serial number (e.g., transformers or battery chargers) .
- Additional Sequence Identifier – Optional letters or numbers for multiple MCCs or panels connected to the same bus .
- Circuit Reference (PC Reference) – Each circuit fed from or incoming to a switchboard or MCC is given a reference number prefixed by the equipment's Electrical Identification Number. Numbering generally starts at the incomers and ascends sequentially by electrical importance .
Example Numbering Table
| Component | Example | Description |
|---|---|---|
| Equipment Category | TB | Terminal Box |
| Unit Number | 05 | Fifth unit in the plant |
| Voltage Number | 20 | 13.8 kV secondary voltage |
| Serial Number | 03 | Third piece of this equipment type |
| Single Letter | A | First of multiple identical units |
| Circuit Reference | P410-01 | First circuit from switchboard P410 |
Labeling Guidelines
- Labels should be permanent, legible, and placed on the front of the equipment.
- Include voltage, current rating, and last update date for safety .
- Modular boxes should allow easy upgrades and clear identification of each circuit.
- Follow local electrical codes and standards such as AS/NZS 3000, AS/NZS 61439, or equivalent .
Summary
A well-structured numbering system ensures safe operation, easy maintenance, and clear documentation. Each distribution box or panel should have a unique identifier combining equipment type, voltage, serial number, and circuit reference, with optional letters for multiple identical units. Proper labeling improves safety, troubleshooting, and compliance in both residential and industrial installations.
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