What is the Resistance of a Copper Bus Bar

Copper Bus Bars are a critical component in modern electrical and power distribution systems. Understanding what is the resistance of a copper bus bar is essential for engineers, OEMs, and industrial buyers to ensure efficient power transmission, minimal energy loss, and safe operation of high-current systems. This article explains the factors affecting copper bus bar resistance, provides calculation methods, explores applications, and highlights key advantages.

1. What is the Resistance of a Copper Bus Bar?

A copper bus bar is a solid or laminated conductor used to carry high currents in power systems, including switchgear, battery modules, EVs, and UPS systems. Its resistance depends on several factors, including material, cross-sectional area, length, and temperature.

The electrical resistance $\mathrm{<span\; style="font-size:\; 16px;">R</span>}$RR of a copper bus bar can be calculated using the formula:

$$\mathrm{<span\; style="font-size:\; 16px;">R</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">\rho </span>}\frac{\mathrm{<span\; style="font-size:\; 16px;">L</span>}}{\mathrm{<span\; style="font-size:\; 16px;">A</span>}}$$R = \rho \frac{L}{A}R=ρAL

Where:

• $\mathrm{<span\; style="font-size:\; 16px;">R</span>}$RR = resistance (Ω)

• $\mathrm{<span\; style="font-size:\; 16px;">\rho </span>}$\rhoρ = resistivity of copper ($\mathrm{<span\; style="font-size:\; 16px;">1.68</span>}<span\; style="font-size:\; 16px;">\times </span>{\mathrm{<span\; style="font-size:\; 16px;">10</span>}}^{<span\; style="font-size:\; 16px;">-</span>\mathrm{<span\; style="font-size:\; 16px;">8</span>}}\mathrm{<span\; style="font-size:\; 16px;">\Omega </span>}<span\; style="font-size:\; 16px;">\cdot </span>\mathrm{<span\; style="font-size:\; 16px;">m</span>}$1.68 × 10^{-8} Ω·m1.68×10−8Ω⋅m at 20°C)

• $\mathrm{<span\; style="font-size:\; 16px;">L</span>}$LL = length of the bus bar (m)

• $\mathrm{<span\; style="font-size:\; 16px;">A</span>}$AA = cross-sectional area (m²), i.e., width × thickness

This formula allows engineers to design high current busbar systems with minimal energy loss.

2. Factors Affecting Copper Bus Bar Resistance

Material

• Pure copper has the lowest resistance and is widely used in laminated busbars and power busbar systems.

• Copper alloys or copper-plated aluminum may slightly increase resistance.

Geometry

• Wider or thicker bus bars reduce resistance.

• Longer bus bars increase resistance proportionally.

Temperature

• Copper’s resistance increases with temperature. The temperature coefficient of copper is approximately 0.00393/°C.

• High-temperature applications require adjustments in design to maintain performance.

Surface Treatment

• Plating such as tin, nickel, or silver primarily affects contact resistance in Electrical Busbar connectors, not the bulk resistance of the bus bar itself.

3. Example Calculation of Copper Bus Bar Resistance

Consider a copper bus bar with the following specifications:

• Length $\mathrm{<span\; style="font-size:\; 16px;">L</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">1</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}$L = 1 mL=1m

• Width $\mathrm{<span\; style="font-size:\; 16px;">W</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">50</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">0.05</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}$W = 50 mm = 0.05 mW=50mm=0.05m

• Thickness $\mathrm{<span\; style="font-size:\; 16px;">T</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">5</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">0.005</span>}\mathrm{<span\; style="font-size:\; 16px;">m</span>}$T = 5 mm = 0.005 mT=5mm=0.005m

The cross-sectional area:

$$\mathrm{<span\; style="font-size:\; 16px;">A</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">W</span>}<span\; style="font-size:\; 16px;">\times </span>\mathrm{<span\; style="font-size:\; 16px;">T</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">0.05</span>}<span\; style="font-size:\; 16px;">\times </span>\mathrm{<span\; style="font-size:\; 16px;">0.005</span>}<span\; style="font-size:\; 16px;">=</span>\mathrm{<span\; style="font-size:\; 16px;">0.00025</span>}{\mathrm{<span\; style="font-size:\; 16px;">m</span>}}^{\mathrm{<span\; style="font-size:\; 16px;">2</span>}}$$A = W × T = 0.05 × 0.005 = 0.00025 m²A=W×T=0.05×0.005=0.00025m2

Resistance:

$$\mathrm{<span\; style="font-size:\; 16px;">R</span>}<span\; style="font-size:\; 16px;">=</span>\frac{\mathrm{<span\; style="font-size:\; 16px;">1.68</span>}<span\; style="font-size:\; 16px;">\times </span>{\mathrm{<span\; style="font-size:\; 16px;">10</span>}}^{<span\; style="font-size:\; 16px;">-</span>\mathrm{<span\; style="font-size:\; 16px;">8</span>}}<span\; style="font-size:\; 16px;">\times </span>\mathrm{<span\; style="font-size:\; 16px;">1</span>}}{\mathrm{<span\; style="font-size:\; 16px;">0.00025</span>}}<span\; style="font-size:\; 16px;">\approx </span>\mathrm{<span\; style="font-size:\; 16px;">6.72</span>}<span\; style="font-size:\; 16px;">\times </span>{\mathrm{<span\; style="font-size:\; 16px;">10</span>}}^{<span\; style="font-size:\; 16px;">-</span>\mathrm{<span\; style="font-size:\; 16px;">5</span>}}\mathrm{<span\; style="font-size:\; 16px;">\Omega </span>}$$R = \frac{1.68 × 10^{-8} × 1}{0.00025} ≈ 6.72 × 10^{-5} ΩR=0.000251.68×10−8×1≈6.72×10−5Ω

This extremely low resistance demonstrates why copper bus bars are ideal for high current busbar applications.

4. Laminated Copper Bus Bars and Resistance Reduction

For industrial and EV applications, laminated busbars are often used to further reduce resistance and inductance:

• Multiple copper layers laminated with insulating material

• Compact design allows low-resistance, high-current capacity

• Supports electrical busbar connectors and flexible layouts for battery systems

5. Applications of Copper Bus Bars

Copper bus bars with low resistance are widely used in:

• EV battery modules – high-efficiency connections for Battery Bus Bar connectors

• Industrial power distribution – power busbar for switchgear and inverters

• UPS and data centers – safe, compact power routing

• Renewable energy systems – solar inverters, wind turbines

• Laminated Flexible Busbars – absorbing vibration and thermal expansion

Low resistance ensures high efficiency, reduced heat generation, and reliable operation.

6. Advantages of Low-Resistance Copper Bus Bars

• Minimal voltage drop across high-current systems

• High efficiency for power electronics and EV modules

• Improved thermal performance with reduced heating

• Enhanced reliability in critical applications

• Compact and customizable designs, especially with laminated busbars

7. FAQ – Copper Bus Bar Resistance

Q1: What is a typical resistance for a copper bus bar?
A: For standard industrial bus bars, resistance is very low, usually in the range of micro-ohms to milliohms, depending on length, width, and thickness.

Q2: How does temperature affect bus bar resistance?
A: Resistance increases with temperature. For copper, the temperature coefficient is ~0.00393/°C.

Q3: Can laminated busbars reduce resistance?
A: Yes, laminated busbars reduce resistance and inductance, offering more compact and efficient high current busbar solutions.

Q4: What applications require low-resistance copper bus bars?
A: EV battery systems, UPS, industrial power distribution, renewable energy inverters, and any high-current electronics.