BusBar Amps Calculator
Determine the current capacity of busbars
BusBar Amps Calculator
Compliant with IEC 61439 & NEC Article 368 Principles
Results:
Total Area (A_total): 0.00 mm²
Current Density (J): 0.00 A/mm²
Base Current (I_base): 0.00 A
Proximity Factor (Kp): 0.00
Env. Factor (Kenv): 0.00
Rated Current (I_rated): 0.00 A
Short-Circuit (I_th): 0.00 kA
Resistance (R): 0.00 mΩ
Total Power Loss (P_total): 0.00 W
Est. Load Power (P): 0.00 kW
How to Use the Calculator
1. Enter Busbar Specs
- Enter the Width (mm) and Thickness (mm) of a single busbar.
- Input the Number of Bars used in parallel for each phase.
- Select the busbar Material (Copper or Aluminum).
2. Define Conditions
- Choose the Enclosure Type to determine the base current density (J).
- Select the Bar Spacing to set the proximity effect factor (Kp).
- Enter the Ambient Temperature and Altitude to find the environmental correction factor (Kenv).
3. Set System Parameters
- Enter the Busbar Length (m) to calculate resistance and power loss.
- Input System Voltage and Power Factor to estimate the total load power (kW).
- Set the Fault Duration (s) (typically 1s) to find the short-circuit withstand capacity.
How to Calculate Busbar Amps from Size (as per IEC & NEC)
Step 1 – Define Inputs
Start by gathering these values:
- Busbar width (W) in mm
- Busbar thickness (T) in mm
- Number of bars (Nbars)
- Material (Cu or Al)
- Ambient temperature (Ta)
- Spacing (S) & Enclosure
- System voltage (V)
Step 2 – Calculate Area
The area of one bar is:
A = W × T
For multiple bars per phase:
A_total = A × Nbars
Example (80x10mm):
A = 80 × 10 = 800 mm²
Step 3 – Get Base Current
Base current depends on current density (J):
- Cu (enclosed): ~1.3 A/mm²
- Cu (ventilated): ~2.0 A/mm²
- Al (enclosed): ~1.0 A/mm²
I_base = A_total × J
Example (Cu, enclosed):
I_base = 800 × 1.3 = 1040 A
Step 4 – Apply Corrections
(a) Proximity (Kp):
- Spacing ≈ T: Kp = 0.90
- Spacing ≥ T: Kp = 0.95
- Stacked: Kp = 0.85
(b) Environment (Kenv):
Derate for Ta > 40°C or Altitude > 1000m.
I_rated = I_base × Kp × Kenv
Example:
I_rated = 1040 × 0.90 × 1.0 = 936 A
Step 5 – Check Short-Circuit
The thermal withstand (1s) is:
I_th(1s) = k × A_total
- k = 80 (Copper)
- k = 55 (Aluminum)
For 't' seconds:
I_th(t) = I_th(1s) ÷ √t
Example (Cu, 1s):
I_th(1s) = 80 × 800 = 64,000 A (64 kA)
Step 6 – Find Resistance
Use resistivity (ρ) at 90°C:
- Cu: ρ = 0.021 Ω·mm²/m
- Al: ρ = 0.034 Ω·mm²/m
R = (ρ × L) ÷ A_total
Example (1m Cu):
R = (0.021 × 1) ÷ 800
R = 0.00002625 Ω
Step 7 – Find Power Loss
Power loss per phase (using I_rated):
P_loss = I_rated² × R
Total 3-phase loss:
P_total = 3 × P_loss
Example (Cu):
P_loss = 936² × 0.00002625 = 22.9 W
P_total = 3 × 22.9 = 68.7 W
Step 8 – Estimate Load Power
The 3-phase load (kW) is:
P(kW) = √3 × V × I_rated × PF ÷ 1000
Example (400V, 0.9 PF):
P = 1.732 × 400 × 936 × 0.9 ÷ 1000
P = 584 kW
Step 9 – Final 80x10mm Rating
A single 80x10mm Copper bar (enclosed, 40°C) is rated for:
- Area: 800 mm²
- Rated Amps: 936 A
- Short-Circuit: 64 kA (1s)
- Load @ 400V: ~584 kW
Note: Always verify with manufacturer data. These are estimates based on IEC/NEC principles.
Busbar Amp Chart (Typical Ratings)
This table shows approximate ampacities for common busbar sizes based on the formulas above (enclosed, 40°C, Kp=0.9).
| Busbar Size (W x T) (mm) | Busbar Area (mm²) | Estimated Busbar Amps (A) | Material |
|---|---|---|---|
| 40 x 10 mm | 400 mm² | ~468 A | Copper |
| 60 x 10 mm | 600 mm² | ~702 A | Copper |
| 80 x 10 mm | 800 mm² | ~720 A | Aluminum |
| 80 x 10 mm | 800 mm² | ~936 A | Copper |
| 100 x 10 mm | 1000 mm² | ~1170 A | Copper |
FAQs
1. How to calculate busbar amps?
To calculate busbar amps, first find the busbar’s cross-sectional area using the formula A = Width × Thickness. Then multiply by the current density, which depends on the material and environment. For example, use I = A × J, where J is about 1.3 A/mm² for copper in an enclosed setup. Apply correction factors for proximity and temperature, using I_rated = A × J × Kp × Kenv. Example: an 80×10 mm copper bar gives I = 80 × 10 × 1.3 × 0.9 = 936 A.
2. What size is a 400 amp busbar?
To size a busbar for 400 A, reverse the formula: A_required = I ÷ (J × Kp × Kenv). For copper at 1.3 A/mm², Kp = 0.9, Kenv = 1.0, you get A_required = 400 ÷ (1.3 × 0.9) = 342 mm². A practical size is 40×10 mm (400 mm²), which easily carries 400 A.
3. What size is a 600 amp busbar?
Using the same method, A_required = 600 ÷ (1.3 × 0.9) = 513 mm². A 60×10 mm copper bar (600 mm²) fits this rating. The expected current capacity is I = 600 × 1.3 × 0.9 = 702 A, giving safe headroom above 600 A.
4. What size is a 800 amp busbar?
Calculate required area as A_required = 800 ÷ (1.3 × 0.9) = 684 mm². The nearest standard bar is 80×10 mm (800 mm²). The estimated capacity is I = 800 × 1.3 × 0.9 = 936 A, which comfortably handles 800 A continuous.
5. What size busbar is needed for 1000 amps?
For a 1000 A copper busbar, A_required = 1000 ÷ (1.3 × 0.9) = 854 mm². You can use a single 100×10 mm bar (1000 mm²) or two 50×10 mm bars in parallel per phase. The calculated ampacity is I = 1000 × 1.3 × 0.9 = 1170 A, ensuring reliable performance and compliance with IEC 61439 and NEC 368 guidelines.