Calculate current capacity, voltage drop, and temperature rise for electrical bus bars. This calculator helps electrical engineers, panel builders, and power system designers to properly size and evaluate bus bars.
A bus bar is a metallic strip or bar used in electrical distribution systems to conduct and distribute electrical power. Bus bars are typically made of copper, aluminum, or brass, and are used in power distribution panels, switchgear, and other electrical equipment.
The current capacity or ampacity of a bus bar is the maximum current it can carry continuously without exceeding its temperature rating. The ampacity depends on several factors:
Current Capacity Formula:
I = J × A
Where:
Voltage drop is the reduction in voltage along a bus bar due to its resistance. Excessive voltage drop can cause equipment to malfunction or operate inefficiently.
Voltage Drop Formula:
Vdrop = I × R
Where:
Temperature rise is the increase in temperature of a bus bar above the ambient temperature when current flows through it. Excessive temperature rise can damage insulation, cause connections to loosen, and reduce the lifespan of the bus bar.
Temperature Rise Formula:
ΔT = (I² × R) / (h × S)
Where:
The resistance of a bus bar depends on its material, length, and cross-sectional area.
Resistance Formula:
R = ρ × L / A
Where:
| Material | Resistivity (Ω·m at 20°C) | Temperature Coefficient (/°C) | Typical Current Density (A/mm²) |
|---|---|---|---|
| Copper | 1.68 × 10-8 | 0.00393 | 2-4 |
| Aluminum | 2.82 × 10-8 | 0.00403 | 1.2-2 |
| Brass | 6.39 × 10-8 | 0.0020 | 1-1.5 |
| Silver | 1.59 × 10-8 | 0.0038 | 4-6 |
Multiple bus bars can be connected in parallel to increase current capacity. However, the effective capacity is not simply the sum of individual capacities due to mutual heating and proximity effects. The spacing between bars affects current distribution and cooling.