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Busbar joint integrity is vital for safe, reliable operation of bus assemblies. Carefully follow manufacturer guidance on approved installation procedures, torque requirements, electrical testing and maintenance. Using qualified installers and conducting regular inspections also helps identify any overheating issues early. Properly executed busbar splices, terminations and alignment verifies a robust busbar system free of high resistance connections.
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Busbars are highly conductive metal bars used to distribute power in electrical switchgear and panelboards. Multiple busbar sections are interconnected to form the bus assembly. The joints between busbar sections are critical to the safety and reliable performance of the bus system.
Proper alignment, tight connections and low contact resistance at joints are essential to:
This guide covers busbar joint splicing procedures, termination best practices and troubleshooting of overheating connections. Following manufacturer instructions for acceptable hardware, torque levels and electrical testing will result in a robust busbar system.
Splicing is joining together two busbar sections in an assembly using bolted joints. Here are some best practices:
The busbars must perfectly align without any gaps. If misalignment exceeds 10% of busbar thickness, overheating can result.
Apply the recommended torque on bolts to create proper contact pressure without crushing. Insufficient torque leads to loose connections while overtorque damages bus and bolts.
The step-by-step tightening procedure ensures proper stress distribution and prevent busbar warping.
After assembly, test electrical continuity across joints. Resistance should not exceed the design maximum (eg: 100 μΩ).
Cable terminations connect external cables carrying incoming or outgoing power to the busbar.
Two-hole lugs rated for the cable size provide secure crimped connections. Lug bolt hole spacing should match busbar holes.
Apply oxidation inhibitor paste on aluminum cable and lug contact surfaces to avoid oxidization and increased resistance.
Use anti-galling agents and proper torque to prevent aluminum adhesion when tightening.
Follow cable and lug manufacturer guidance on proper torque levels to apply on termination hardware.
Wrap exposed section of cables with insulating tape or boot. Provide insulating covers on cable lugs if they contact busbar body.
Hot busbar joints indicate high resistance connections that can worsen over time.
Use micro-Ohmmeter to measure resistance across suspect joints. Compare to baseline values to identify poor connections.
Insufficient torque leads to loose joints and localized heating at contact points due to high resistance.
Corrosion of aluminum busbars forms insulating oxide layer causing heat rise. Re-torque with anti-oxidant coating.
Presence of dirt, moisture, oil etc. increases resistance across joints leading to heating. Clean thoroughly before re-torqueing.
Frequent large load cycles can loosen bolts over time. Check for loose joints and re-torque. Use Belleville washers to compensate.
Proper busbar joint construction ensures a robust, low resistance connection.
Allowance for thermal expansion prevents stressing of joints. Use expansion joints at suitable intervals.
Solid or laminated copper sleeves over bolted joints avoid contact between dissimilar metals.
Minimum two bolts recommended for each busbar joint for even contact pressure. More bolts needed for higher currents.
Use appropriate high strength bolts and washers for busbars. Belleville/cup washers compensate for bolt relaxation.
Bring sections into perfect alignment, apply oxidation inhibitor on contact surfaces, install proper bolts and washers through holes, and systematically tighten bolts to specified torque levels. Follow manufacturer’s step-by-step procedure.
After alignment, lightly hand tighten bolts, tighten to 30% torque, re-tighten to 60% torque, and finally tighten to full rated torque. Torque all bolts in cross pattern. Always follow OEM procedure.
Use compatible high current lugs crimped to cables. Align lugs to busbar bolt holes. Use anti-oxidant paste on aluminum. Tighten bolts to cable manufacturer’s specified torque levels. Insulate exposed cables.
Torque levels for busbar bolt sizes are generally: M8 – 23 Nm M10 – 45 Nm
M12 – 79 Nm Always follow OEM recommendations for proper torque.
Torque for stainless steel bolts is lower than steel bolts. Tighten only up to the hardware manufacturer’s recommended levels to avoid overtorque damage while ensuring proper contact pressure. Do not assume standard torque data.
Improper alignment, low torque, corrosion, contamination between surfaces, cyclic loading, poor bolt design can all increase resistance across the joint leading to heating at connections.
Clearly mark busbar orientation for reassembly in same position. No section rotation. Align busbar axes perfectly with no offset. Align all bolt holes accurately. Do not force or bend busbars when splicing.
Avoid bending busbars when aligning. Bending deforms the cross-section, work hardens the metal, and can fracture the copper grain structure. All of this increases resistance at the joint.
Follow manufacturer bolt torque procedure, use oxidation inhibitors, properly align busbars when splicing, select compatible bolt/lug materials, and conduct electrical testing after assembly to identify any high resistance connections.
Use OEM approved hardware like stainless steel bolts and Belleville washers. Apply recommended torque for the bolts. Do not make any new holes in busbar. Ensure supports are adequately spaced.
Misalignment, low contact pressure, surface contamination, corrosion, loose connections, material incompatibility can all increase contact resistance and cause busbar joint overheating.
Use a micro-Ohm meter with suitable low resistance range. Measure resistance across each joint and compare with acceptable baseline value provided by busbar manufacturer to identify problem joints.
Copper or tin-plated copper sleeves over bolted joints help avoid contact between dissimilar metals like copper and aluminum busbars which can accelerate galvanic corrosion.
Minimum two bolts recommended per busbar joint. More bolts needed for higher current capacity like 4-8 bolts for 2000A to 4000A busbars. Follow manufacturer guidance on bolt quantities.
Anti-oxidants help avoid insulating oxide layer formation which increases resistance and heating of aluminum busbar joints. But proper torque levels are still needed to prevent physical loosening.
Busbar systems are tested for dielectric withstand capability, temperature rise under rated current, short circuit strength, and mechanical vibrations as part of certification to standards like UL-845 and IEC 61439.
Busbar bolts should be checked and re-torqued at least annually as part of preventive maintenance. For systems prone to vibrations, more frequent 6 month inspection may be required.
Heat shrink covering provides additional electrical insulation over a bolted busbar joint. It may be required at joints with reduced clearance or for higher voltage systems above 600V.
Recommended tools are torque wrenches, micro-Ohmmeter, feeler gauges, callipers, oxidation inhibitor, marking pens, insulating tapes, and lifting equipment. Use insulated tools for live work.
For guidance on proper joint design, number of bolts, torque levels, splice sleeves, electrical testing procedures, suitability for cyclic loads, and to obtain any UL or IEC certifications for the busbar system.
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