Cable and Busway Selection Guide for Power Distribution
A practical guide for selecting cables and busways in power distribution systems. Covers ampacity calculation, voltage drop, installation methods, and cost comparison.
本文为中文技术阅读版本，工程参数、标准和项目边界仍应以正式图纸、技术协议和书面报价为准。
Cable vs Busway: When to Use Which
Cables: Flexible, cheaper for small currents (<400A), easier to route around obstacles.
Busways: Compact, higher current capacity (up to 6300A), easier installation for long runs, better for future expansion.
Rule of thumb: Use busway for main distribution (>800A), cables for branch circuits (<400A).
Cable Selection Criteria
1. Current carrying capacity (ampacity): Based on conductor size, insulation type, installation method, ambient temperature.
2. Voltage drop: Should be <3% for feeders, <5% total (NFPA 70, IEC 60364).
3. Short-circuit withstand: Cable must withstand fault current until protection operates.
4. Insulation type: PVC (cheaper), XLPE (higher temperature), LSZH (low smoke zero halogen for public buildings).
Busway Selection Criteria
Current rating: Standard ratings 250A, 400A, 630A, 800A, 1000A, 1250A, 1600A, 2000A, 2500A, 3200A, 4000A, 5000A, 6300A.
Type: Air-insulated (AIS) or sandwich type (compact).
IP rating: IP54 for indoor, IP65 for outdoor or humid areas.
Tap-off points: Every 1-3 meters for plug-in busway.
Installation Best Practices
Cables: Use cable trays, not conduit (easier maintenance). Support every 1-1.5m.
Busways: Support every 2-3m. Allow for thermal expansion (expansion joints every 30-40m).
Both: Keep separate from hot pipes, avoid sharp bends, label clearly.
Cost Comparison
For short runs (<50m): Cables usually cheaper.
For long runs (>50m) with high current: Busway often cheaper (less installation labor).
For future expansion: Busway cheaper (easy to add tap-off units).
Example: 1000A feeder, 100m length. Cable cost: $30k, Busway cost: $35k. But busway installation labor 50% less.
Common Selection Mistakes
1. Undersizing (voltage drop too high)
2. Wrong insulation (cable melts in high temperature)
3. Poor installation (cable damaged during pulling)
4. No spare capacity (can't add future loads)
5. Ignoring harmonic distortion (cables overheat with non-linear loads)