Copper Busbars in Switchgear: What Engineers Need to Consider

A copper busbar rarely operates by itself.

Inside a switchgear or switchboard assembly, it becomes part of a much larger electrical and mechanical system.

It connects incoming power to distribution circuits. It passes through supports and connection points. It sits near insulation systems, terminals, circuit breakers and other conductive parts. It generates heat while carrying current and may be exposed to substantial electromagnetic forces during a short circuit.

The busbar therefore has to do more than carry current.

It has to fit, connect, insulate, withstand, and operate reliably inside the complete assembly.

This is where busbar engineering becomes assembly engineering.

For low-voltage power switchgear and controlgear assemblies, IEC 61439 provides the principal framework. IEC 61439-2:2020 covers power switchgear and controlgear assemblies with rated voltages up to 1,000 V AC or 1,500 V DC.

The important lesson is simple:

A busbar cannot be engineered correctly without understanding the system in which it will operate.

The Busbar Is Part of the Assembly

A busbar drawing can look like an independent mechanical component.

In reality, its final performance depends on its surroundings.

Consider a typical switchgear assembly.

The busbar may interact with:

• incoming terminals;

• circuit breakers;

• disconnectors;

• supports;

• insulating barriers;

• enclosure walls;

• outgoing connections;

• other busbars;

• protective devices;

• cables;

• grounding systems.

Every interface introduces another engineering consideration.

This means a busbar should not be designed only from its own dimensions.

The surrounding assembly has to be considered as well.

The Five Questions Behind a Good Busbar Design

When integrating a busbar into switchgear, five fundamental questions appear again and again.

1. Can it carry the required current?

This is the electrical and thermal question.

2. Can it maintain the required insulation distances?

This is the insulation-coordination question.

3. Can it withstand the mechanical forces?

This becomes particularly important during short-circuit conditions.

4. Can it connect reliably to the surrounding equipment?

Connection geometry and contact quality matter.

5. Can the complete assembly satisfy its applicable requirements?

The busbar is only one part of the final assembly.

These questions are connected.

Changing one can affect another.

1. Current-Carrying Capacity

The first requirement is usually obvious:

The busbar must carry the required current without exceeding the permitted thermal conditions.

As discussed in the previous article, current creates resistive losses:

P=I2RP = I^2R

The resulting heat must be dissipated through the surrounding system.

That means current-carrying capability depends on more than copper cross-sectional area.

It can depend on:

• conductor dimensions;

• material resistivity;

• ambient temperature;

• conductor arrangement;

• surface condition;

• enclosure;

• airflow;

• nearby conductors;

• number of loaded circuits.

IEC 61439 treats temperature rise at the assembly level rather than treating every conductor as an isolated component. IEC 61439-1:2020 introduced the concept of group rated current for circuits within a loaded assembly, which reflects the fact that several circuits may contribute to the same thermal environment.

This is an important distinction:

The busbar’s thermal performance is influenced by the assembly around it.

2. Temperature Rise Inside the Assembly

A busbar carrying current becomes hotter than its surroundings.

But the surrounding air also becomes hotter.

Inside an enclosure, this can create a thermal chain:

Busbar losses

↓

Busbar temperature

↓

Internal air temperature

↓

Enclosure heat transfer

↓

External environment

The enclosure therefore becomes part of the thermal system.

IEC TR 60890:2022 provides a calculation method for temperature rise within certain low-voltage assemblies, taking into account factors such as power losses, enclosure characteristics and cooling conditions.

This is why a busbar that performs acceptably in open air cannot automatically be assumed to behave identically inside a compact enclosure.

More Copper Does Not Automatically Solve Everything

A common engineering reaction to thermal problems is:

“Make the busbar bigger.”

Increasing cross-sectional area can reduce resistance.

But it can also change:

• physical dimensions;

• surface area;

• spacing;

• airflow;

• enclosure volume;

• mechanical loads;

• connection geometry.

A thicker busbar may have lower resistance while creating different thermal or mechanical conditions.

The correct design therefore considers the whole geometry, not simply the amount of copper.

3. Clearance and Creepage

Current capacity is only one side of the problem.

A busbar also exists at a particular electrical potential relative to other conductive parts.

That creates insulation requirements.

Two terms are particularly important:

Clearance

The shortest distance through air between conductive parts.

Creepage distance

The shortest distance along the surface of an insulating material between conductive parts.

They are related, but they are not the same thing.

For low-voltage equipment, IEC 60664-1 provides the fundamental insulation-coordination framework and includes requirements for determining clearances, creepage distances and solid insulation. The current consolidated IEC 60664-1:2020+AMD1:2025 version applies to equipment up to 1,000 V AC or 1,500 V DC and addresses factors including pollution conditions and altitude.

This means a busbar’s physical geometry cannot be considered independently from its insulation environment.

Voltage Changes the Design

A busbar carrying 1,000 A is not completely described by saying:

1,000 A busbar

The operating voltage also matters.

A high-current low-voltage system and a high-current system at a substantially different voltage can require different insulation arrangements.

The engineer therefore has to consider at least:

• working voltage;

• rated insulation voltage;

• overvoltage category where applicable;

• pollution degree;

• material characteristics;

• altitude;

• surrounding insulation;

• required clearances and creepage distances.

The copper cross-section solves only part of the problem.

Pollution and the Real Environment

Insulation does not exist in a laboratory.

Real assemblies may encounter:

• dust;

• moisture;

• condensation;

• industrial contamination;

• conductive deposits.

These conditions can influence the required creepage distance and insulation-coordination strategy.

This is why clearance and creepage cannot be selected from a generic “voltage table” without understanding the applicable conditions.

IEC 60664-1 specifically incorporates environmental factors into insulation coordination.

For the busbar manufacturer, this has a practical implication:

The required geometry may depend on the environment in which the finished component will be installed.

4. Busbar Spacing

Spacing between busbars is not simply empty space.

It can influence:

• electrical insulation;

• magnetic fields;

• thermal behavior;

• mechanical support;

• assembly accessibility.

For example, two adjacent phase conductors carry currents that generate electromagnetic fields.

Their arrangement therefore matters during fault conditions and can also matter for AC losses.

Spacing is consequently both an electrical and mechanical design parameter.

Three-Dimensional Geometry Matters

A busbar can be electrically correct in a 2D drawing but impossible to install in the real assembly.

Consider a formed busbar that must pass:

• around a breaker;

• through a support;

• between insulation barriers;

• toward a terminal;

• around another conductor.

The actual three-dimensional geometry determines whether the component fits.

This is why formed busbars should be treated as precision 3D components rather than simply bent strips of copper.

5. Connection Points

A busbar may carry thousands of amperes.

But the electrical path still has to pass through physical connections.

Common interfaces include:

• bolted joints;

• breaker terminals;

• cable lugs;

• flexible connectors;

• other busbars;

• terminal blocks.

Every interface adds another potential source of resistance.

The basic relationship remains:

P=I2RP = I^2R

If a connection has unnecessarily high contact resistance, it can generate localized heating.

At high current, even a small resistance can matter.

Contact Surfaces Matter

A good electrical connection depends on more than simply tightening a bolt.

The connection can be affected by:

• contact area;

• surface condition;

• plating;

• contact pressure;

• fastener arrangement;

• joint design;

• contamination;

• oxidation;

• mechanical stability.

This is why busbar connection surfaces are often treated differently from other surfaces.

A manufacturer may need to provide:

• bare copper;

• tin-plated copper;

• silver-plated surfaces;

• other specified finishes.

The correct surface treatment depends on the intended connection system and environment.

Why Plating Can Be Useful

Copper already has excellent electrical conductivity.

So why plate it?

Because the contact interface has requirements beyond bulk conductivity.

A suitable surface treatment can improve:

• corrosion resistance;

• contact stability;

• environmental durability;

• compatibility with mating surfaces.

But plating should not be viewed as a universal improvement.

The appropriate treatment depends on the connection system and application.

The engineering question is:

What does the interface require?

Not:

Which plating is the most expensive?

6. Mechanical Support

A busbar is also a mechanical structure.

It has weight.

It experiences vibration.

It may be subjected to assembly forces.

And during a short circuit, electromagnetic forces can become very significant.

This means the busbar must be properly supported.

Important factors can include:

• support material;

• support spacing;

• conductor geometry;

• fastening method;

• bend configuration;

• connection constraints.

A long unsupported busbar and a closely supported busbar do not behave mechanically in the same way.

Short-Circuit Forces

This is one of the most important differences between normal operation and fault conditions.

During a short circuit, current can become much higher than the normal operating current.

The electromagnetic force between conductors increases strongly with current.

In simplified terms, magnetic force is related to the interaction between current and magnetic field.

The exact force depends on:

• current magnitude;

• conductor geometry;

• conductor spacing;

• current direction;

• support arrangement;

• fault duration.

The resulting forces can act on:

• busbars;

• supports;

• insulators;

• connections;

• mounting structures.

Therefore:

A busbar that is mechanically adequate during normal operation may still require separate short-circuit consideration.

Why Support Spacing Matters

Imagine two otherwise identical busbars.

One is supported frequently.

The other has long unsupported spans.

The second will generally experience larger mechanical deflection and higher mechanical demands for a given loading condition.

During a short circuit, the difference becomes even more important because electromagnetic forces can be substantial.

This is why support layout is part of busbar engineering.

The busbar and its supports should be treated as one mechanical system.

7. Insulators and Supports

Busbar supports perform several functions simultaneously.

They may provide:

• electrical insulation;

• mechanical support;

• positioning;

• separation;

• short-circuit force resistance.

The support therefore has to be selected according to the complete application.

Questions can include:

• What voltage is present?

• What mechanical forces are expected?

• What temperature will the support experience?

• What environment is it exposed to?

• What material properties are required?

• How is the support attached?

The busbar cannot be separated completely from the component holding it.

8. Enclosure Effects

The enclosure changes the environment around the busbar.

It can influence:

• heat dissipation;

• airflow;

• condensation;

• accessibility;

• insulation distances;

• mechanical protection.

IEC 62208:2023 covers empty enclosures intended for use as part of low-voltage switchgear and controlgear assemblies, including enclosures for indoor and outdoor applications up to 1,000 V AC or 1,500 V DC.

But an important distinction remains:

The enclosure is not the complete assembly.

The final assembly manufacturer remains responsible for the complete assembled system and the applicable product requirements.

This is another reason a busbar supplier needs to understand the customer’s installation environment.

9. Busbar Insulation

Not every busbar needs to be insulated.

But where insulation is required, the insulation system becomes part of the design.

Possible solutions include:

• sleeves;

• heat-shrink insulation;

• molded insulation;

• epoxy systems;

• powder coatings;

• barriers;

• phase separators.

The choice depends on the application.

Insulation can provide:

• electrical separation;

• protection against accidental contact;

• environmental protection;

• controlled creepage paths.

But insulation can also change the thermal behavior of the busbar.

A coated conductor may dissipate heat differently from an exposed conductor.

Therefore:

Electrical insulation and thermal design must be considered together.

10. Bends and Electrical Clearances

A bend can create a new spatial relationship between conductors.

A flat bar may have sufficient clearance in one orientation.

After bending, another section may approach:

• another phase;

• an enclosure wall;

• a grounded component;

• an insulating barrier.

This is why clearance checks need to be performed on the finished three-dimensional geometry, not just on the flat blank.

The manufacturing process can therefore directly affect electrical safety.

11. Tolerances Can Affect Assembly

Suppose a busbar drawing specifies:

• hole position;

• bend angle;

• bend location;

• overall length.

Each dimension has a tolerance.

The finished component therefore exists within a range of possible geometries.

If several tolerances accumulate toward the same connection interface, the final position can shift.

That can affect:

• breaker alignment;

• terminal alignment;

• bolt installation;

• clearance;

• insulation spacing.

This is why critical interface dimensions deserve particular attention during manufacturing.

The Busbar and the Mating Component Must Agree

A busbar is only half of a connection.

The other half may be:

• a breaker;

• terminal;

• connector;

• cable lug;

• another busbar.

The interfaces must be compatible.

That can involve:

• hole pattern;

• bolt size;

• contact surface;

• plating;

• orientation;

• available space;

• tightening requirements.

A perfectly manufactured busbar can still fail to integrate if the interface definition is incomplete.

12. Short-Circuit Conditions Need a Different Mindset

Normal current is only one operating condition.

A switchgear assembly also has to consider fault conditions defined by the applicable product and system requirements.

During a fault:

Current rises dramatically

↓

Electromagnetic forces rise

↓

Mechanical loading increases

↓

Connections and supports are stressed

↓

Thermal and mechanical consequences must be considered

This is why busbar design cannot be based only on rated current.

The component has to be compatible with the assembly’s fault-duty requirements.

The Busbar Is Part of a Current Path

A useful way to think about a switchgear busbar is not as an isolated conductor but as part of a complete current path:

Source

↓

Incoming connection

↓

Busbar

↓

Switching/protection device

↓

Outgoing conductor

↓

Load

Every interface contributes something.

A weak connection can compromise an otherwise excellent busbar.

A poorly supported section can compromise an otherwise excellent electrical design.

A poorly controlled clearance can compromise an otherwise excellent current path.

The system has to work as a whole.

13. What the OEM Needs to Define

For a busbar manufacturer, a useful customer specification should ideally contain enough information to understand the intended application.

Depending on the project, that can include:

Electrical

• rated current;

• voltage;

• AC/DC;

• frequency;

• duty;

• short-circuit requirements.

Geometry

• 3D geometry;

• dimensions;

• bend positions;

• holes;

• slots;

• connection features;

• tolerances.

Material

• copper grade;

• temper;

• applicable material standard.

Surface

• bare copper;

• tin;

• nickel;

• silver;

• other treatment.

Insulation

• required or not;

• insulation system;

• required coverage;

• relevant electrical requirements.

Assembly

• mating components;

• support positions;

• installation orientation;

• available clearances;

• enclosure conditions.

Quality

• inspection requirements;

• documentation;

• traceability;

• acceptance criteria.

The more complex the component, the more important this information becomes.

A Good Busbar Drawing Is More Than a Shape

For simple parts, a drawing can communicate most of the required information.

For complex busbars, the technical definition may need to cover:

• material;

• geometry;

• tolerances;

• surface;

• insulation;

• interfaces;

• inspection.

The drawing should therefore answer:

What exactly is the finished component?

Not merely:

What does it look like?

This distinction is particularly important when the component will be produced repeatedly.

From Customer Drawing to Manufacturing

Once the specification is complete, the busbar manufacturer translates it into a manufacturing process.

That process may involve:

Engineering review

↓

Material selection

↓

Blank development

↓

Machining strategy

↓

Bending strategy

↓

Surface treatment

↓

Inspection plan

↓

Production

The manufacturer may identify issues before production begins.

For example:

• impossible bend sequence;

• insufficient bend radius;

• inaccessible machining feature;

• unrealistic tolerance;

• problematic plating area;

• insufficient clearance;

• ambiguous reference dimensions.

This engineering feedback is valuable.

It can prevent a manufacturing problem from becoming a production problem.

Design for Assembly

A good busbar should not only be manufacturable.

It should also be easy to integrate into the customer’s assembly.

That can mean:

• clear connection orientation;

• sensible bolt access;

• predictable bend geometry;

• controlled insulation;

• correct marking;

• appropriate packaging;

• consistent dimensions.

A busbar that is difficult to install can increase assembly time and create opportunities for errors.

The best component is therefore one that works well before, during, and after installation.

The Manufacturer Is Part of the Engineering Chain

This is particularly relevant for OEMs.

A busbar supplier is not simply a company that cuts copper according to a drawing.

For complex components, the supplier can contribute knowledge about:

• material;

• forming;

• machining;

• tolerances;

• plating;

• insulation;

• manufacturability.

That engineering feedback can improve the final component.

The relationship becomes:

OEM design

↔

Busbar manufacturing engineering

rather than:

OEM drawing

↓

anonymous fabrication

A Practical Integration Checklist

Before releasing a complex copper busbar into production, it is useful to ask:

Electrical

• Is the rated current defined?

• Is the voltage defined?

• Is AC/DC operation defined?

• Are frequency and duty relevant?

• Are short-circuit requirements known?

Thermal

• Is the allowable temperature rise understood?

• Is the installation enclosed?

• Are neighboring heat sources known?

• Is the surface condition defined?

Mechanical

• Are support locations defined?

• Are fault forces considered?

• Are connection forces understood?

Insulation

• Are clearance requirements known?

• Are creepage requirements known?

• Is the pollution environment defined?

• Is altitude relevant?

• Is insulation or plating required?

Manufacturing

• Is the copper grade defined?

• Is the temper defined?

• Are tolerances realistic?

• Is the bend sequence manufacturable?

• Can the finished component be inspected?

Interface

• Are mating components defined?

• Are connection holes and surfaces controlled?

• Are installation clearances verified?

This checklist is not a substitute for the applicable standards.

It is simply a way to make sure the engineering conversation is complete.

The Most Important Principle

The most important lesson from all of this is:

A busbar is not finished when it carries the required current.

It is finished when it performs its required function inside the intended assembly.

That means:

• carrying current;

• remaining within thermal limits;

• maintaining required insulation;

• surviving mechanical conditions;

• connecting reliably;

• fitting correctly;

• remaining manufacturable and repeatable.

That is the real engineering definition of a successful busbar.

The COUPLAGE Perspective

This is where copper busbar manufacturing becomes more than metal fabrication.

The physical component sits at the intersection of several engineering disciplines:

Electrical

Current, resistance, voltage and losses.

Thermal

Temperature rise and heat dissipation.

Mechanical

Geometry, supports and fault forces.

Insulation

Clearance, creepage and insulation systems.

Manufacturing

Cutting, machining, forming, plating and inspection.

A good busbar has to satisfy all of them simultaneously.

For an OEM, this means the best busbar supplier is not simply the one that can produce copper shapes.

It is the supplier that understands the engineering requirements behind the shape.

Final Thoughts

A copper busbar may be physically simple, but its role inside switchgear is not.

Once installed in a real assembly, the busbar becomes part of a system involving current, heat, insulation, mechanical forces, connections, supports and enclosure conditions.

IEC 61439-2:2020 establishes specific requirements for power switchgear and controlgear assemblies, while IEC 60664-1 provides the broader insulation-coordination framework for low-voltage equipment.

The important lesson is not that every busbar must be designed by applying every standard directly.

The lesson is that the applicable requirements belong to the complete application, and the busbar has to be engineered so that it can function correctly within that application.

A good busbar therefore begins with copper.

But it ends with integration.

The best busbar is not simply the one that carries the current. It is the one that fits the electrical, thermal, mechanical and insulation requirements of the system around it.

That is what turns a copper component into an engineered component.

What to Explore Next

The busbar is now designed, manufactured and integrated into the assembly.

But there is one final question:

How do we know the finished busbar actually meets the requirements we specified?

Material certificates, dimensional inspection, electrical checks, surface inspection, traceability, testing and documentation all become part of the answer.

The next article will look at the other side of precision manufacturing:

How to Specify and Inspect Copper Busbars: Tolerances, Quality and Documentation

References

1. IEC 61439-1:2020, Low-voltage switchgear and controlgear assemblies — Part 1: General rules, International Electrotechnical Commission.
   Provides the general rules and verification framework for low-voltage assemblies.

2. IEC 61439-2:2020, Low-voltage switchgear and controlgear assemblies — Part 2: Power switchgear and controlgear assemblies.
   Defines specific requirements for power switchgear and controlgear assemblies, including assemblies up to 1,000 V AC or 1,500 V DC.

3. IEC 60664-1:2020+AMD1:2025, Insulation coordination for equipment within low-voltage supply systems — Part 1: Principles, requirements and tests.
   Provides the insulation-coordination framework covering clearances, creepage distances and solid insulation for applicable low-voltage equipment.

4. IEC TR 60890:2022, A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation.
   Provides a calculation method for temperature rise within applicable low-voltage assemblies.

5. IEC 62208:2023, Empty enclosures for low-voltage switchgear and controlgear assemblies — General requirements.
   Covers empty enclosures intended to form part of low-voltage switchgear and controlgear assemblies.

6. ASTM B187/B187M-26, Standard Specification for Copper, Bus Bar, Rod, and Shapes and General Purpose Rod, Bar, and Shapes.
   Provides requirements relevant to copper conductor bar, rod and shapes, including material, dimensional, mechanical and electrical characteristics.