| Case | Phase | kW | V | PF | Material | Length (m) | Req. Current (A) | Selected (A) | V-drop (%) | SC Check |
|---|---|---|---|---|---|---|---|---|---|---|
| Example 1 | 3 | 120 | 400 | 0.92 | Copper | 30 | 272.5 | 300 | 1.69 | PASS |
| Example 2 | 3 | 480 | 480 | 0.88 | Aluminum | 80 | 850.0 | 1000 | 7.49 | FAIL |
| Example 3 | 1 | 35 | 230 | 0.95 | Copper | 25 | 268.7 | 300 | 2.73 | PASS |
- Effective load (kW): kW × Demand ÷ Diversity × (1 + Growth%)
- Base current (A):
3-phase: I = (kW × 1000) / (√3 × V × PF × η)1-phase: I = (kW × 1000) / (V × PF × η)
- Required current (A):
Ireq = I × Continuous × Harmonic × Material ÷ (Ambient × Installation)
- Voltage drop:
3-phase: ΔV = √3 × Ireq × (R·cosφ + X·sinφ) × L1-phase: ΔV = 2 × Ireq × (R·cosφ + X·sinφ) × LΔV% = (ΔV / V) × 100
Ambient, installation, impedance, and short-circuit withstand values are simplified defaults for quick planning. For final procurement, replace these with your chosen manufacturer catalog data.
- Enter system phase, voltage, and total connected load in kW.
- Set power factor and efficiency based on equipment or estimates.
- Apply demand, diversity, and future expansion to reflect reality.
- Choose installation and ambient temperature for derating effects.
- Add harmonic multiplier for non-linear loads, if applicable.
- Enter the busway run length and the allowable voltage drop limit.
- Set required short-circuit level from fault studies or standards.
- Click Calculate to view the selected rating and checks.
- Use CSV/PDF exports to attach results to design notes.
Load characterization for busway planning
Start with connected kW, then apply demand and diversity to reflect realistic peak conditions. For example, 480 kW at demand 0.90 and diversity 1.10 becomes 480×0.90÷1.10=392.7 kW before growth. Adding 20% expansion raises it to 471.3 kW, improving long-term flexibility.
Current calculation aligned with site parameters
The calculator converts effective kW to current using voltage, power factor, and efficiency. On a 480 V three‑phase system with PF 0.88 and η 0.96, the base current is computed using I=(kW×1000)/(√3×V×PF×η). This approach ensures sizing follows the electrical loading, not just nameplate kW.
Thermal derating and operating margin
Busway capacity depends on heat dissipation. Ambient temperature and installation conditions apply derating factors. Continuous loads are treated conservatively using a 1.25 multiplier. At 45 °C with outdoor shaded routing, the combined derating reduces allowable current, which can shift selection to the next standard rating.
Voltage drop and loss checks for long runs
Voltage drop is calculated from per‑meter resistance and reactance using the run length and the required current. Keeping drop within 2–5% supports equipment performance and reduces nuisance trips. The loss estimate (I²R) helps compare alternatives such as shorter routes, higher ratings, or improved power factor.
Short-circuit withstand and coordination
A selected busway must withstand available fault current until protective devices clear. This tool compares a simplified withstand rating against your entered short‑circuit requirement. If the check fails, review higher withstand options, shorter feeder impedance, or protection settings to maintain coordination and safety.
- 3φ, 400 V, 120 kW, PF 0.92, η 0.95, L=30 m → typical selection around 250–300 A depending on factors.
- 3φ, 480 V, 480 kW, PF 0.88, η 0.96, L=80 m → larger rating may be driven by derating and voltage drop.
- 1φ, 230 V, 35 kW, PF 0.95, η 0.93, L=25 m → selection commonly lands in 200–300 A range.
1) What does “required current” represent?
It is the base load current adjusted for continuous operation, harmonics, material allowance, and derating from ambient temperature and installation conditions.
2) Why does continuous load apply a 125% factor?
Continuous loading can heat conductors over long periods. Applying a conservative margin helps maintain temperature limits and improves reliability under sustained demand.
3) How should I choose demand and diversity factors?
Use project load studies, equipment schedules, and historical utilization. Demand reflects expected peak use, while diversity accounts for loads that seldom peak at the same time.
4) What harmonic multiplier should I use?
For offices or mostly linear loads, use 1.00. For VFDs, UPS, or dense electronics, consider 1.10–1.30 based on measured THD and manufacturer guidance.
5) Why can voltage drop drive a larger busway rating?
Long runs increase impedance effects. A higher rating generally lowers resistance, reducing voltage drop and losses, which can be necessary to meet performance limits.
6) Is the short-circuit check a replacement for fault studies?
No. It is a screening check. Final selection should use verified available fault current, protective device clearing times, and manufacturer withstand and bracing ratings.
7) How do I use the CSV and PDF downloads?
Run a calculation first, then download. The exports capture key inputs, results, and checks for design reviews, client submittals, and internal documentation.