A busbar may have excellent electrical conductivity on paper, but that doesn’t always mean the complete connection will perform the same way.

In many electrical and battery applications, the problem starts at the connection point. A poorly designed hole, uneven contact surface, loose joint, unsuitable plating, or incorrect dimensions can increase contact resistance. Over time, that small increase can contribute to heat generation, voltage loss and unreliable electrical performance.

This is why contact resistance deserves attention when selecting or designing a custom busbar.

For manufacturers and engineers sourcing from a copper busbar manufacturer in India, the focus shouldn’t be only on copper grade or busbar thickness. The complete connection — material, dimensions, surface condition, holes, bends and joint design — needs to work together.

What Exactly Is Busbar Contact Resistance?

Busbar contact resistance is basically the electrical resistance at the point of contact between a busbar and the machine or conductor to which it is attached.

Although there may seem to be metal surfaces making complete contact with each other, the microscopic contact area is much less than what seems to be going on. Some influencing factors are roughness of the surface, oxidation, contamination, surface finish, and contact pressure.

In a battery pack, for example, this may occur between the busbar and the battery terminal. In the case of an electrical panel, it can also take place at the connection point with any kind of conductor.

The resistance would have been very low, yet one may generate heat at high currents even at this low resistance level.

Importance of Busbar Contact Resistance

The formula relating the key elements is very simple:

Power loss = I² × R

Where:

• I = current passing through the connection

• R = resistance of the connection

As the current increases, the impact of resistance raises exponentially.

For instance, in an electrical connection that carries hundreds of amperes, the contact location must be chosen with care. Even minor resistance in an unwanted area can turn into a heat source.

In terms of battery and energy distribution, this can affect:

• Energy efficiency

• Voltage drop

• Increase in heat locally

• Reliability of the connection

• Stability of the connection in time

• Performance of the battery pack

• Need for maintenance

New researches on busbars in EV batteries show that contact resistance is one of the key parameters of the connection. The state of the surface and contact pressure are also important in mechanically fixed connections.

What Are the Reasons for High Contact Resistance in Busbars?

There generally isn’t one particular reason. In real-world production and construction, multiple factors are involved.

1. Poor Surface Contact Area

A large-looking contact area doesn’t automatically mean that there is proper electrical contact in the whole area.

Surface roughness, unevenness, burrs, or contamination means that the effective contact area is becoming lower.

For a custom busbar, it is important to consider the contact area at the stage of design, not at the stage of production.

2. Low or Uneven Contact Pressure

Bolted connections in busbars rely heavily on good mechanical contact.

If a connection is not firmly mounted, then the actual contact area will decrease. Excessive pressure can also cause different mechanical complications.

What is important is a properly working and well-designed connection rather than trying to increase the pressure.

3. Oxidization and Surface Pollution

Copper and aluminum can form surface layers that can determine electric contact.

Along with oxidation, dust, oil, and dirt, other foreign matters can interfere with the interface.

This is of great importance in the case when a busbar is used in conditions where moisture, chemical substances, and temperature fluctuations occur.

4. Wrong Design of the Hole or Joint

Busbar connection means more than just a simple metal piece with a hole.

Diameter of the hole, position of the hole, distance from the edges, size of the overlap, and arrangement of the fasteners affect the position of the busbar. Therefore, though a deviation in terms of dimensions might seem insignificant at the time of inspection, it may result in misalignment in assembly.

5. Unsatisfactory Surface Treatment

The type of surface treatment needed depends on the purpose.

In some electric applications, tin plating or nickel plating is necessary to obtain certain surface properties and withstand the environment.

The right choice of the surface depends on the purpose, material of the connecting element, and customer order but not only on the quality of the product.

6. Temperature Fluctuations and Vibration

An interface that works well at the beginning may not be the same after going through several heating and cooling cycles.

Repeated temperature fluctuations may strain the attachment points. Furthermore, vibration may also lead to movement or slow deterioration of the junction. Hence, the design of busbars for applications like EV batteries requires consideration of compatibility other than just manufacturing.

Where Is Contact Resistance Important?

Contact resistance is a factor wherever there is an electric connection formed by a busbar. Its definitions encompass:

Lithium batteries

Busbars provide connections between different battery segments. It is important that the connection remains stable in terms of both electrical and mechanical performance and that it coincides with the layout of the battery.

EV batteries

High-current electric batteries have increased the significance of resistance and heat. The design of the connection should be made with respect to electrical properties and mechanical specifications like vibration and thermal cycling.

Inverters and energy storage

Batteries and inverters are known to have their connections carry large electric currents. Poor connection can lead to unnecessary voltage drop and local heating.

Electrical panels and switchgear

Copper busbars are used widely for electric power transmission in electrical systems. The place of connection calls for proper mechanical and electrical design.

Power distribution systems

Busbars used in electric systems require durable and stable joints during their whole operation life.

How Is Busbar Contact Resistance Tested?

The specific test method employed depends on the application, product specifications, and related standards.

The method of testing low resistance requires the appropriate conditions since even very low values of resistance can also be affected by the leads of the measuring device, points of contact, and other sources of errors.

According to IEC 62812:2019, there are different methods for measuring low resistance and necessary recommendations regarding the test conditions, which should reduce the influence of the factors negatively affecting the accuracy of the measuring process.

In terms of measuring contact resistance, there are methods discussed in IEC 60512-2-1 that involve the use of millivolt value and also methods of specified test current available in IEC 60512-2-2.

In reality, the electrical equipment manufacturers also check the following physical properties, which can have an effect on the performance of the product:

• Dimensions of the equipment

• Hole sizes and positions

• Flatness

• Burrs

• Surface condition

• Plating or surface finish

• Dimensions of bends

• Corresponding perfectly with the specifications provided by the customer.

Thus, the measures against resistance can give valuable information; however, they should not substitute dimensional and visual inspection.

Adinath Enterprises’s Procedures for Making Quality Busbar Connections

At Adinath Enterprises, the busbars are built upon the drawings and instructions given by the clients.

The aim is not to merely manufacture a piece of copper or aluminum strip out of any material but to produce a busbar that meets the particular purpose and assembly specifications.

The manufacturing process may include, depending on requirements, the following operations:

• Analysis of the requirements

• Engineering review and design assistance

• Material selection

• Cutting

• Punching

• Bending

• Drilling

• Tapping

• Chamfering

• Deburring

• Surface treatment

• Dimensional inspection

• Quality inspection

• Packing

When manufacturing custom copper and aluminum busbars, all component features are considered, such as positions of the holes, number of bends, tolerances, thickness, and surface finish, depending on the client’s instructions and technical specification.

This is important for cases when the busbar is to be installed in a limited-size battery assembly, inverter, control panel, or power distribution unit.

Adinath Enterprises specializes in manufacturing customized busbars used in lithium battery packs, electric vehicle batteries, energy storage systems, home inverter batteries, switchgears, control panels, and other electrical systems.

Copper vs. Aluminum: Does Material Matter?

Yes, but this is not the only factor to consider.

Copper has high electrical conductivity and is ideal in applications that require compact, high-current connections.

Aluminum, on the other hand, is lighter but requires more careful engineering in terms of design and weight-saving considerations.

But regardless of the material used in the busbar, it must still be constructed properly.

Two bus bars made of different materials can behave quite differently in terms of surface, heat characteristics, and joining requirements—and this is especially relevant for connections with terminals or with another conductor made of a different material.

Frequent Errors Raising Contact Resistance

There are a few mistakes that keep reappearing in customized busbar projects.

Utilizing a standard busbar without consulting the engineering drawing

Although the busbar can carry the required current, it won’t be installed accurately.

Disregarding the contact zone

Sometimes, engineers concentrate on conductor cross-section dimensions but not enough on the joint.

Making holes of the wrong size

Incorrectly placed or sized holes can cause issues with alignment and contact.

Not eliminating burrs resulting from punching/drilling

The presence of burrs can prevent achieving proper contact and assembly.

Preparing the surface finish regardless of application

Surface finishing should be selected considering the actual electrical, environmental, and mating requirements.

Considering the contact resistance as an issue of testing only

The resistance issue might arise during testing however, this does not mean that it is only a testing problem.

Helpful Tips for Improving Busbar Connections

Make sure to comply with the following:

• Specify the materials and grades used.

• Describe the minimum thickness and the dimensions of the final shape.

• Provide information about hole size and their locations.

• Define the tolerances required for production.

• Provide the necessary information about bends and the forming process needed.

• Indicate the surface quality requirements.

• Provide information about the element that the bus is going to be connected to.

• Check that the contact areas are free of burrs and damage.

• Take into account the current and wattage of the busbar.

• Discuss the design with the manufacturer before the production process starts.

So, following these simple tips will allow you to avoid changes in the project later.

Get the Right Busbar, Starting From the Joint

Busbar performance is not only one of conductivity.

The elements such as material, geometric dimensions, working surface, connection design, tolerances, and manufacturing quality determine how well the manufactured component works.

The companies looking for custom copper or aluminum busbars can avoid numerous connection problems before production thanks to clear illustrations and discussions about the purpose with the manufacturer.

Adinath Enterprises deals with manufacturing custom copper and aluminum busbars according to specification, which can be used in many applications, such as lithium battery packs, electric vehicle systems, inverters, switchboards, and power distribution.

If you have already developed the drawing and have requirements regarding your joint, the earlier you share the particulars with the manufacturer, the smoother the design and manufacturing process will go.