Busbar Systems: Copper or Aluminium? Selection Criteria
Busbar systems: A practical comparison of copper and aluminium busbars in terms of conductivity, cross-section, weight, cost and joint reliability.
ContentsBusbar systems are the backbone of a low voltage switchboard: they carry energy from the incoming device to every outgoing way. Flat conductor profiles are used instead of cables for a simple reason. They move high current in a smaller volume, with lower losses, and they can be tapped anywhere along their length. The material of that backbone directly drives project cost, weight, enclosure size and long term failure risk. And the discussion always starts at the same point: copper or aluminium?
What does a busbar actually do inside the board?
A busbar performs three jobs at once. First, it carries current: whatever the rated current of the incoming device is, the main busbar must carry it continuously without exceeding temperature limits. Second, it provides mechanical strength: during a short circuit the electrodynamic forces between adjacent bars can reach the order of tonnes, and the bar and insulator arrangement must resist them without permanent deformation. Third, it organises distribution, letting dozens of outgoing devices connect to the same potential in a repeatable, inspectable way.
None of these jobs is independent of the material. Conductivity sets the current capacity, density sets the weight and the supporting structure, mechanical properties set the short circuit withstand, and surface behaviour sets the service life of every joint.
Where copper wins
Copper is the reference material of electrical distribution. With a conductivity of roughly 58 MS/m it carries the same current in a noticeably smaller cross-section than aluminium. That translates directly into a more compact board, which becomes decisive when the busbar chamber is narrow, the cubicle depth is limited, or many parallel bars are required.
- Smaller cross-section for the same current, therefore a smaller busbar chamber and a more compact enclosure
- The copper oxide layer that forms on the surface is conductive, so joint resistance is less likely to drift upwards over time
- Higher mechanical strength and modulus, allowing longer spans between insulators under short circuit forces
- Very low creep, so bolted joints lose preload much more slowly
- With tin, nickel or silver plating, extremely low contact resistance at high current transitions
Where aluminium makes sense
Aluminium offers about 61-62 per cent of the conductivity of copper, but only one third of the density. Even when the cross-section has to grow by a factor of roughly 1.6 for the same current, the resulting bar is still lighter than copper. On long main busbar runs and in cost sensitive projects that advantage becomes very visible.
- Weight for the same current is typically less than half that of copper, reducing transport, handling and structural load
- Material cost per unit is far lower and less exposed to price volatility
- Lower total cost of ownership on long main busbar runs and busbar trunking systems
- A larger surface area helps dissipate heat, so temperature rise stays manageable when the section is correct
- Lower site risk related to theft and scrap value
Copper versus aluminium busbar comparison
| Criterion | Copper (Cu) | Aluminium (Al) |
|---|---|---|
| Electrical conductivity | ~58 MS/m (100% IACS reference) | ~37 MS/m (about 61-62% IACS) |
| Cross-section for the same current | Reference | Roughly 1.55-1.65 times larger |
| Weight for the same current | Reference | Around 45-55% lighter |
| Density | 8.9 g/cm³ | 2.7 g/cm³ |
| Material cost | High | Significantly lower |
| Surface oxide | Conductive, joint friendly | Insulating Al₂O₃; surface preparation mandatory |
| Bolted joint behaviour | Stable, slow preload loss | Prone to creep; spring washers and torque control essential |
| Thermal expansion | ~17 µm/m·K | ~23 µm/m·K |
| Typical use | Compact boards, high current density, MV cubicle connections | Long main busbar runs, trunking, cost driven projects |
Six critical points when sizing a busbar
Picking a cross-section straight from a catalogue current rating is the most common mistake. Catalogue values are valid under a defined reference condition, and a real switchboard is never exactly that condition.
- Rated current and diversity: the real load profile may differ from the rating of the incoming device
- Ambient and internal temperature rise: a selection made for 35 °C is invalid in a 50 °C room
- Bar arrangement and proximity effect: bars stacked side by side block each other cooling
- Mounting orientation: a bar mounted on edge cools better than a flat mounted one
- Short circuit withstand: the Icw value drives both the section and the insulator spacing
- IP rating and ventilation: a sealed IP54 enclosure heats up far faster than an IP31 one
All of these parameters must be assessed together with the temperature rise verification required by IEC 61439-1. For the wider context of main busbar selection, see our article on main distribution board selection criteria.
Joints: where failures really begin
Most busbar failures do not start in the bar itself, they start at the joints. Contact resistance rises, the spot heats up, oxidation accelerates, resistance rises further, and the process turns into thermal runaway. With aluminium the risk is higher for two reasons: the insulating oxide layer that forms almost instantly on a fresh surface, and the tendency of the metal to creep, which lets bolt preload decay over time.
The countermeasures are well established. Aluminium surfaces are brushed immediately before assembly and protected with a suitable contact compound. Bolted joints are tightened to the manufacturer specified torque and re-checked after a defined period of service. Spring or conical washers compensate for preload loss. Wherever copper meets aluminium directly, a bimetallic connector or tin plating prevents galvanic corrosion. Recording joint temperatures with a thermal camera after commissioning creates a baseline for every later inspection.
Plating: bare, tin, nickel or silver
- Bare copper: an economical choice indoors, in low humidity, on accessible joints
- Tin plating: the most common option, it delays oxidation and makes copper to aluminium joints safe
- Nickel plating: durable at high temperature and in aggressive atmospheres, with slightly higher contact resistance than tin
- Silver plating: the lowest contact resistance, preferred for isolating contacts in withdrawable systems and high current transitions
Key takeaways: busbar systems
- What does a busbar actually do inside the board — A busbar performs three jobs at once.
- Where copper wins — Copper is the reference material of electrical distribution.
- Where aluminium makes sense — Aluminium offers about 61-62 per cent of the conductivity of copper, but only one third of the density.
- Six critical points when sizing a busbar — Picking a cross-section straight from a catalogue current rating is the most common mistake.
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
Does using aluminium make the switchboard bigger?
Yes. For the same current the cross-section grows by roughly 1.6 times, which usually shows up as a taller busbar chamber or a deeper enclosure. In exchange the weight drops and the supporting structure gets lighter, so unless floor space is critical the increase is acceptable in most projects.
Can copper and aluminium busbars be used in the same board?
They can, but the point where the two metals meet is exposed to galvanic corrosion. That interface needs a bimetallic plate, a tin plated surface or a proper transition connector, and it must be included in the torque and thermal inspection plan.
How is a busbar cross-section verified?
Design calculation is only the starting point. Real verification comes from the temperature rise and short circuit withstand verification defined in IEC 61439. Following the rules of a design that has already passed type testing is faster and more reliable than testing every single board.
Related articles
- Busbar Trunking or Cable? Choosing the Right Distribution Method
- Busbar Current Carrying Capacity and Derating Calculation
- Choosing the Incoming Device: MCCB or ACB?
- All technical articles
At Devpan we size the busbar system together with the current profile, short circuit withstand, ambient temperature and site conditions of the project, and we work with type test verified design rules for both copper and aluminium solutions. Share your single line diagram and we can produce a cross-section, weight and cost comparison of both alternatives.
