GRL Copper Busbar: How to Specify Busbars for Motor Control Centers (MCCs)

Motor control centers (MCCs) distribute electrical power to motor starters, drives, feeders, and other equipment within an industrial installation. Inside an MCC, copper busbars provide the main conductive paths that supply power to individual units and distribution circuits.

Selecting copper busbars for an MCC requires more than choosing a cross-sectional area based on current. The design must also account for temperature rise, short-circuit forces, busbar supports, connection geometry, enclosure conditions, and the requirements of the complete electrical assembly.

For OEMs and MCC manufacturers, defining these requirements before ordering custom copper busbars helps ensure that the finished components fit the assembly and meet the intended electrical and mechanical specifications.

How Are Copper Busbars Used in a Motor Control Center?

An MCC typically contains a main power distribution path and connections to individual motor control units or outgoing feeders. Depending on the design, its copper busbar arrangement may include horizontal main busbars, vertical distribution busbars, branch connections, and a separate protective earth or neutral arrangement where required.

The main busbar distributes incoming power along the assembly. Vertical busbars or other distribution conductors supply individual functional units, while designed connection points provide interfaces for breakers, contactors, motor starters, and feeder circuits.

A simplified arrangement is:

Incoming Supply → Main Busbar → Distribution Busbar → Protected Feeder → Motor or Electrical Load

The actual layout depends on the MCC design, rated current, unit configuration, protection arrangement, and installation requirements.

For a copper busbar manufacturer, understanding where the component sits in this arrangement is important. A main busbar, a vertical distribution bar, and a short branch connection may have different dimensions, support conditions, and electrical duties even when they are made from the same copper material.

Which Electrical Ratings Should Be Defined First?

Before selecting the copper busbar dimensions, establish the electrical requirements of the MCC. The busbar needs to match the intended load and the verified ratings of the complete assembly.

The specification should identify the following information where applicable:

The incoming current rating should not be selected by simply adding every motor’s nameplate current without considering the system design. The expected loading, simultaneous operation, specified demand assumptions, and equipment requirements must be coordinated by the responsible electrical designer.

Likewise, a copper busbar’s cross-sectional area alone does not establish the current rating of a complete MCC. The conductor dimensions must be evaluated together with temperature-rise performance, connections, supports, enclosure conditions, and the applicable assembly requirements.

How Does Thermal Performance Affect MCC Busbar Selection?

Temperature rise is one of the main considerations in MCC busbar design. When current flows through a copper conductor, electrical resistance produces heat. If the heat generated exceeds what the assembly can dissipate under its operating conditions, the conductor and surrounding components can become hotter than permitted.

The thermal behavior depends on several interacting factors:

• Conductor dimensions: Width and thickness affect resistance, conductive cross-section, and exposed surface area.
• Current loading: Higher current generally increases resistive heat generation.
• Enclosure design: Cabinet dimensions, internal barriers, and ventilation influence heat dissipation.
• Busbar arrangement: Conductor spacing, orientation, and proximity to other heat sources affect thermal conditions.
• Connection quality: Joint resistance can create local hot spots even when the straight conductor is appropriately sized.
• Температура окружающей среды: Higher ambient temperature reduces the temperature margin available for heat dissipation.

For MCC projects, busbar selection should therefore consider the installed configuration rather than relying solely on a current-density rule or a generic copper cross-section table.

The applicable assembly standard and verification method determine how the required temperature-rise performance is demonstrated. The responsible assembly manufacturer must verify the finished design under the relevant requirements rather than assuming that a busbar component rating alone proves compliance.

What Short-Circuit Requirements Must an MCC Busbar Meet?

An MCC busbar must also withstand the mechanical and thermal effects associated with the specified short-circuit conditions.

During a fault, high current can generate substantial electromagnetic forces between conductors. These forces act on the busbars, joints, and supports. A design that carries the normal operating current successfully may still be unsuitable if its support arrangement cannot withstand the expected fault forces.

The design review should consider:

• Available short-circuit current at the assembly
• Required short-time withstand current and duration, where specified
• Peak withstand current or other applicable peak fault requirements
• Busbar support spacing and support strength
• Conductor arrangement and distance between phases
• Bolted joints, connection plates, and other interfaces
• The protection system and its specified fault-clearing behavior

A larger copper cross-section does not automatically guarantee an adequate short-circuit rating. The busbar geometry, support system, connections, and complete assembly arrangement must be compatible with the required fault performance.

For this reason, custom busbar dimensions should be reviewed alongside the MCC manufacturer’s approved design and verification requirements.

How Should Horizontal and Vertical MCC Busbars Be Specified?

Horizontal main busbars and vertical distribution busbars often have different physical arrangements and electrical duties. Their specifications should reflect these differences rather than applying the same dimensions to every section of the assembly.

Main Horizontal Busbars

The main horizontal busbar generally distributes power along the MCC lineup. Its specification should identify the required current rating, conductor arrangement, support points, connection locations, and provisions for adjoining sections or future extensions where applicable.

The finished dimensions must also fit the enclosure and maintain the clearances and mechanical support defined by the assembly design.

Vertical Distribution Busbars

Vertical busbars supply individual units or groups of outgoing circuits. Their geometry depends on the arrangement of the functional units, connection points, barriers, and mounting hardware.

Important details include the location of branch connection points, terminal interfaces, mounting holes, support positions, and the required alignment with the equipment.

Branch Connections and Joint Plates

Branch conductors and joint plates connect sections of the distribution system. Their dimensions and contact areas should match the mating components, fasteners, and specified connection method.

Hole position, overlap length, surface finish, and tightening requirements may be particularly important because a connection defect can create localized heating or mechanical stress.

Which Copper Material and Surface Finish Should Be Specified?

Copper busbars for MCCs are commonly selected for their electrical conductivity and suitability for fabrication. However, the material specification should be defined according to the engineering design rather than assuming that every copper grade or material condition is interchangeable.

When preparing a custom busbar specification, consider:

• Copper grade: Identify the required grade or applicable material standard.
• Material condition: Specify the required temper or mechanical condition when relevant to forming and mechanical performance.
• Обработка поверхности: State whether bare copper, tin plating, silver plating, or another specified finish is required.
• Contact interfaces: Identify surfaces that must meet specific connection or plating requirements.
• Traceability: Define any material documentation or batch identification required by the project.

Surface treatment should be selected according to the contact design, operating environment, and project requirements. No single plating option is automatically best for every MCC connection.

The sequence of cutting, punching, bending, joining, and surface treatment can also affect the finished component. This should be considered when the drawing includes close tolerances, complex geometry, or specific requirements for the contact areas.

What Should an MCC Manufacturer Provide to a Copper Busbar Supplier?

A clear technical package helps the busbar supplier understand the required geometry and manufacturing scope. It also reduces the risk of producing components that meet individual dimensions but do not fit the intended assembly.

For a custom MCC busbar order, provide the following information where applicable:

A dimensioned 2D drawing should define critical dimensions and interfaces. For complex busbar arrangements, a 3D model can help communicate bend direction, mounting position, clearance, and the spatial relationship between adjacent conductors.

The busbar supplier and assembly manufacturer should also clarify which party is responsible for assembly-level electrical verification. Manufacturing a copper component to the approved drawing does not by itself establish the rated current or short-circuit performance of the complete MCC.

Which Standards Apply to MCC Busbar Design?

The applicable standard depends on the market, equipment type, and project requirements.

For IEC-based low-voltage power switchgear and controlgear assemblies, IEC 61439-2:2020 defines specific requirements for power switchgear and controlgear assemblies, while IEC 61439-1:2020 provides the general rules for the series, including technical characteristics and verification requirements.

For North American motor control centers, UL 845 is the relevant standard for motor control centers. The standard’s official listing records a revision dated February 28, 2025.

The correct standard and edition should be confirmed for each project. Meeting a component drawing or a general busbar calculation does not automatically demonstrate compliance of the assembled equipment. Temperature rise, short-circuit performance, insulation, and other applicable requirements must be addressed through the assembly’s required design verification.

Common MCC Busbar Specification Mistakes to Avoid

• Selecting dimensions from current alone: The complete design must also account for temperature rise, supports, connection geometry, and required short-circuit performance.
• Ignoring enclosure conditions: Internal layout, ventilation, and surrounding heat sources influence the thermal performance of the installed busbar.
• Leaving hole positions unclear: An incorrect hole pattern can make installation difficult or place mechanical stress on connection points.
• Using the same specification for every busbar section: Main, vertical, branch, neutral, and grounding conductors may have different functions and requirements.
• Leaving the surface finish undefined: The required copper finish and functional contact surfaces should be stated on the drawing.
• Confusing component supply with assembly verification: The completed MCC must meet its own applicable ratings and verification requirements.

Specifying copper busbars for motor control centers requires coordinated electrical, thermal, mechanical, and manufacturing information. Rated current, temperature-rise requirements, short-circuit performance, conductor geometry, supports, material, surface finish, and connection details all influence the finished design.

The most effective approach is to define the MCC’s electrical requirements first, establish the required busbar arrangement, and then specify the dimensions and manufacturing details for each component. Critical interfaces should be reviewed before production so that the copper busbars fit the intended assembly and remain consistent with the approved design.

GRL Copper provides customized copper busbar fabrication according to customer drawings and application requirements. For MCC projects, supplying clear material specifications, dimensions, connection details, tolerances, surface treatment, and relevant technical requirements helps establish the manufacturing scope before production begins.