Busbar connections in low-voltage switchgear require careful design of contact areas, tightening torque, and mechanical support to ensure safe, reliable, and thermally stable power distribution.

Overview of Busbar Function

In low-voltage switchgear, busbars act as the backbone of the electrical system, distributing power from the main incoming supply to branch circuits and outgoing feeders. They are typically made of copper or aluminum and can be rigid, flat, tubular, or laminated depending on current requirements and space constraints . Proper busbar design ensures thermal stability, mechanical strength, and electrical integrity, preventing overheating, deformation, or failure under normal and short-circuit conditions .

Connection Principles

Contact Area

• The contact area (Sc) between busbars must be sufficient to handle the rated current without excessive heating. For main busbar continuity links, the contact area should be at least five times the cross-section of the bar (Sc > 5 × Sb) .
• For branch busbars, the contact area can be smaller but must still comply with the same principle to ensure reliable current transfer.
• Connection plates should have full-surface contact to maintain low resistance and optimal heat dissipation.

Contact Pressure and Fastening

• Busbar connections are secured using screws or bolts, with the size, number, and tightening torque selected according to the current rating and bar dimensions .
• Proper torque ensures sufficient contact pressure without exceeding the bolt's elastic limit, which could cause creep or loosening over time.
• Devices such as paint marks or brittle coatings can indicate loosening and verify correct tightening.

Shaping and Alignment

• Busbars must be machined, bent, and shaped carefully to avoid introducing mechanical stresses that could weaken the bar or create hotspots .
• Rigid busbars are commonly used for main connections due to their stability, while flexible or laminated busbars may be used where vibration or movement occurs .

Standards and Verification

• Low-voltage switchgear must comply with IEC 61439, which specifies requirements for temperature rise, short-circuit withstand, dielectric properties, and protection against electric shock .
• Verification can be done through testing, calculation, or comparison with reference assemblies, ensuring that busbar connections meet safety and performance benchmarks.
• For North American applications, UL 1558 and IEEE C37.20.1 are relevant standards, while European assemblies follow IEC 61439-1 for general construction and verification .

Best Practices

• Ensure full-surface contact for main busbars and branch connections.
• Use the correct number and size of screws with proper torque to maintain contact pressure.
• Avoid sharp bends or stress points during shaping to prevent mechanical failure.
• Verify temperature rise and short-circuit withstand according to IEC 61439 or applicable regional standards.
• Consider thermal expansion, vibration, and maintenance access when designing busbar layouts. By following these principles, low-voltage switchgear busbar connections can achieve high reliability, safety, and long-term performance, while minimizing maintenance and operational risks .