Rigid busbar
Flat, round or tubular bars for main current distribution in switchgear, distribution boards, substations and busway. Cut, drilled, punched and bent to the panel layout.
Power distribution conductors
Electrical Busbar Solutions: Aluminium & Copper-Clad Aluminium
A busbar is a solid metal conductor, usually a flat bar, tube or laminated stack, that collects and distributes current inside switchgear, panels, transformers, substations and battery systems. The right busbar balances conductivity, temperature rise, weight, joint reliability and cost. Metline supplies rigid, laminated, flexible, insulated and earthing busbars in aluminium and copper-clad aluminium, cut, punched, bent and plated to your drawing, to customers worldwide; copper bars are covered here as the sizing reference.
- Materials
- Al 1350/6101, CCA
- Types
- Rigid · laminated · flexible · earth
- Finishes
- Tin, nickel, silver, insulation
- Standards
- ASTM B236 · B317 · EN 13601 · IEC 61439
What a busbar does and why design matters
Busbars replace bundles of cable wherever large currents have to be collected, split or carried over short distances. Being solid and rigid, they are compact, easy to tap, mechanically strong against short-circuit forces and dissipate heat well.
Three questions drive busbar design. First, how much current, and at what allowable temperature rise, which sets the cross-section and material. Second, what short-circuit current the system must withstand, which sets support spacing and bar strength against electromagnetic forces. Third, how the bars are joined: most busbar failures occur at bolted joints, where poor contact causes heating, oxidation and eventually burn-out.
Assemblies in low-voltage switchgear are verified for temperature rise and short-circuit withstand under IEC 61439, and in North America under UL 891 and UL 857 for switchboards and busways. The bar material and finish must therefore be chosen as part of the whole assembly design, not in isolation.
Types of electrical busbar
Laminated busbar
Thin conductor layers separated by insulating film and bonded into one stack. Very low inductance, compact and repeatable, used in inverters, converters and battery systems.
Flexible busbar
Stacks of thin foil or strip, welded or pressed at the ends, sometimes insulated. Absorbs vibration, thermal expansion and assembly tolerances at transformer and battery connections.
Braided connector
Woven fine-wire braid with crimped or pressed terminals for moving or vibrating connections and earthing straps.
Insulated busbar
Rigid bar with epoxy powder coating, heat-shrink sleeve or moulded insulation to reduce phase spacing and protect against contact.
Earthing and bonding bar
Drilled bars, traditionally tinned copper and increasingly tin-plated aluminium, for centralised earthing and equipotential bonding in panels, data centres and telecom rooms.
Distribution busbars are laid out in single-phase, single-phase plus neutral, three-phase and three-phase plus neutral arrangements; hole patterns and spacings follow the cabinet design or the device manufacturer's connection drawings.
Aluminium, copper or copper-clad aluminium?
| Property | Copper (Cu-ETP, C11000) | Aluminium 1350 | Aluminium 6101-T6/T61 | Copper-clad aluminium |
|---|---|---|---|---|
| Conductivity | ≥ 100 % IACS | about 61 % IACS | about 55 – 57 % IACS | Between Al and Cu, by clad ratio |
| Density | 8.89 g/cm³ | 2.70 g/cm³ | 2.70 g/cm³ | about 3.3 – 4 g/cm³ |
| Mass for equal resistance (Cu = 1) | 1.00 | about 0.50 | about 0.55 | about 0.6 – 0.7 |
| Strength | Medium (hard-drawn) | Low (H1x tempers) | Medium; can be bent and holds shape | Low to medium |
| Thermal expansion | 17 × 10⁻⁶ /°C | 23 × 10⁻⁶ /°C | 23 × 10⁻⁶ /°C | about 20 × 10⁻⁶ /°C |
| Typical use | Compact, high-current panels and equipment | Large switchgear, busway, substations | Busway, structural bus, tubular bus | Cost-reduced panels needing copper contact surfaces |
Copper gives the smallest cross-section for a given current, which matters in compact equipment. Aluminium needs about 1.6 times the cross-section for the same resistance, but the larger bar also has more surface for cooling, so in practice an aluminium bar of roughly 1.3 – 1.6 times the copper area often meets the same temperature rise, at about half the weight and typically much lower metal cost. Copper-clad aluminium places a copper skin, bonded metallurgically, around an aluminium core, giving copper contact surfaces with reduced weight.
Sizing a busbar: current, temperature and short-circuit
Final ratings must come from the assembly verification or a recognised table (such as DIN 43670 for aluminium and DIN 43671 for copper), because rating depends on enclosure, ventilation, bar arrangement, finish and ambient temperature. As a first approximation, designers often use the following current densities for bare bars in ventilated enclosures:
| Material | Typical starting current density | Example: 1,000 A |
|---|---|---|
| Copper | about 1.2 – 2.0 A/mm² | roughly 500 – 800 mm², e.g. 80 × 10 mm |
| Aluminium | about 0.8 – 1.2 A/mm² | roughly 850 – 1,250 mm², e.g. 100 × 10 mm or 2 × 60 × 10 mm |
Indicative only. Wide, thin bars mounted edgewise cool better than square sections; several parallel bars spaced apart carry more current per unit area than one thick bar; and AC skin and proximity effects reduce the useful area of thick bars at high currents.
- Set the temperature riseAgree the permitted rise above ambient (often 30 – 65 K depending on standard, joint finish and insulation class).
- Choose the sectionStart from tables or current density, then check temperature rise by calculation or test, including joints.
- Check short-circuit withstandCalculate peak electromagnetic force and thermal energy (I²t) for the fault level and duration, and set support spacing and bar thickness to suit.
- Allow for expansionLong aluminium runs need expansion joints or flexible links; aluminium grows about 2.3 mm per metre per 100 K.
Bolted joints, plating and aluminium-to-copper connections
- Prepare the surface: remove aluminium's oxide film by wire-brushing or abrading immediately before assembly and apply an oxide-inhibiting joint compound.
- Maintain contact pressure: use high-tensile bolts with Belleville (conical spring) washers and large flat washers, tightened to the specified torque. Aluminium creeps under pressure; spring washers maintain clamping force through thermal cycles.
- Plate where appropriate: tin plating gives stable contact resistance on aluminium and copper; silver plating is used for high-temperature or high-current contacts; nickel plating gives a hard, corrosion-resistant surface.
- Avoid direct Al–Cu contact in damp conditions: use tinned surfaces, bimetallic (Al-Cu) transition plates or copper-clad aluminium so that galvanic corrosion cannot develop at the joint.
- Inspect with thermography: infrared surveys under load reveal joints with rising resistance before they fail.
Fabrication and finishing options
| Process | What it covers | Notes |
|---|---|---|
| Cutting | Saw or shear cutting to length, deburred | Length tolerances to drawing |
| Punching and drilling | Round holes, slots and hole patterns for terminals | CNC punching for repeatable patterns |
| Bending | Flat (easy-way) and edgewise (hard-way) bends, offsets and twists | Bend radius depends on alloy, temper and thickness; 6101-T61/T63 bends more easily than T6 |
| Machining | Counterbores, contact faces, complex connectors | For connection blocks and special parts |
| Plating | Tin, nickel, silver; full or selective at contact areas | Plating thickness to specification |
| Insulation | Epoxy powder coating, heat-shrink sleeve, PVC dip, laminated films | Dielectric rating to the system voltage |
For fabrication in-house, Metline also supplies busbar stock: rolled and extruded aluminium flat bar in 1350, 1060, 6101 and 6063, copper-clad aluminium bar, and coiled aluminium busbar strip for automatic production lines.
Where electrical busbars are used
Switchgear and panels
Main and distribution bars, droppers and neutral and earth bars in LV and MV switchboards and motor control centres.
Substations
Rigid tubular bus and flat-bar connections between transformers, breakers and disconnectors.
Busway (bus duct)
Enclosed aluminium or copper bars that replace heavy cable runs in factories, data centres and high-rise buildings.
Transformers and rectifiers
Low-voltage terminations, flexible links and high-current DC bus in electrolysis and smelting plants.
Battery and energy storage
Module and rack interconnects, laminated DC bus and flexible links that absorb cell swelling and vibration.
Earthing systems
Main earthing terminals and equipotential bonding bars in industrial, telecom and data-centre facilities.
How to order busbars from Metline
- Send the drawingMaterial and temper, section, length, hole and slot pattern, bends, finish and insulation, or the electrical requirement if you need help selecting.
- ReviewWe confirm manufacturability, tolerances, plating and test documents, and quote delivery terms (EXW, FOB, CIF or DAP).
- Approve samplesFirst-article samples or dimensional reports can be supplied before batch production.
- ShipParts are packed to protect plated contact faces, with an EN 10204 3.1 material certificate and inspection report.
References and standards
- ASTM B236 – Aluminum Bars for Electrical Purposes (Bus Bars)
- ASTM B317/B317M – Aluminum-Alloy Extruded Bar, Rod, Tube, Pipe, Structural Profiles, and Profiles for Electrical Purposes (Bus Conductor)
- EN 13601 – Copper and copper alloys: copper rod, bar and wire for general electrical purposes
- IEC 61439-1 – Low-voltage switchgear and controlgear assemblies: general rules
- DIN 43670 – Aluminium busbars: dimensioning for continuous current
Electrical busbars: frequently asked questions
Is an aluminium busbar as good as copper?
Electrically it can do the same job if it is sized correctly: roughly 1.3 – 1.6 times the copper cross-section, depending on cooling. It weighs about half as much and usually costs less. Copper is preferred where space is tight or joints cannot be maintained properly.
Which aluminium alloy is best for busbar?
1350 (or 1060/1070) gives the highest conductivity for rolled or extruded bus bar. 6101 in T6, T61, T63 or T64 temper is used when the bar must also carry mechanical load or hold bends; each temper trades strength for conductivity.
Why are busbars tin plated?
Tin keeps contact resistance low and stable by preventing oxide build-up, and it protects aluminium-to-copper joints from galvanic corrosion. It is the standard finish for aluminium bus contact faces.
What current can a 100 × 10 mm aluminium busbar carry?
As a rough guide, about 1,000 – 1,200 A for a single bare bar in a ventilated enclosure at moderate temperature rise. The true rating depends on enclosure, arrangement, AC or DC, finish and ambient temperature, so confirm with DIN 43670-type tables or assembly testing.
What is a laminated busbar used for?
Laminated busbars stack thin conductors and insulation films to achieve very low inductance and compact, repeatable connections, mainly in inverters, converters, motor drives and battery systems.
Can you make busbars from my drawing?
Yes. Send a drawing with the aluminium or CCA material, section, hole pattern, bends and finish. We can supply finished busbars or aluminium bar stock and coil for your own fabrication, shipped worldwide.
Need aluminium busbars or busbar stock?
Send your drawing or current requirement. Our team will reply with material options, documentation and a delivered quote.
