Busbars And Cables

2024-01-25 · 14 min read
wiring

Busbars and cables are electrical conductors that move current from Point A ⟶ Point B, but you should consider which is ideal for your application.

busbar

Busbars

A busbar is an object made from a sheet of copper. It typically has through holes where terminates, at its simplest it has a hole for Point A and one for Point B. The busbar's form may become complex—with multiple turns and bends—depending on where the terminations Point A and Point B are positioned.

Cables

Cables and Wires are synonymous for this description (though cables sometimes refer to routings with multiple wires wrapped in a single jacket). For this desription; a cable is a single conductor, with an insulation jacket. In vehicle design, a cable is always stranded, since solid core cables fail over time due to fatigue from vibration. Cables are rarely soldered or welded at their terminations, Points A and B. Cables that conduct large currents are terminated with a crimp, like a Ring Terminal or Lug.

Compare

Both busbars and cables accomplish the main goal of moving an electric current from Point A to Point B. Choosing between the 2 is often an intuitive design decision, but these are the main considerations for a trade study:

Consideration Busbar Cable
1 Electrical Functionality
  • Many thicknesses and widths of copper bar.
  • Many thicknesses of copper sheet and plate.
  • mm² options.
  • AWG options (American Wire Gauge).
2 Electical Termination
  • Through holes.
  • Threaded holes.
  • Captive, pressed fasteners.
  • Captive, pressed termainals
    such as Methode Power Solution's Embedded Bud Connector.
  • Many, including Ring Terminals and Lugs.
3 Mechanical Movement
  • Not intended to move in service.
  • Can move in service, but the designer should consider the lifetime number of movements, and the cable's minimum bend radius. The cable manufacturer's datasheet should include allowable operating conditions.
4 Thermal Expansion
  • Needs to be considered during design. Bends and other features can add predictable deformation areas, rather than allowing a long busbar to buckle in service.
  • This is not usually a concern, since installed cables have bends where thermal deformation will localize.
5 Space Claim
  • Often much smaller than a cable.
  • The rectangular cross section, and 90° bend angles allow for tight packaging in an electronics enclosure.
  • Need to consider the installation process's dynamic space claim, especially when using threaded studs.
  • Cable's minimum bend radius needs to be considered in tight spaces.
  • Cable is stiffer near crimped terminals, since the wire strands cannot slip relative to each other.
  • A cable's circular cross section takes more effective area than an equivalent busbar's rectangular cross section.
6 Design Time
  • 3D modeling time.
  • Mechanical drafting time.
  • May skip Mechanical 3D modelling, depending on the project.
  • Electrical drafting and BOM, to define the cable's requirements.
7 Build Time, Component
  • Some of the processes can be automated or done in batches, like laser cutting, CNC bending, and powder coating.
  • Machines exist for cutting and stripping wire jackets to defined lengths, but they require setup.
  • Much of the crimping setup is manual, needing to be repeated for each cable built.
8 Build Time, System
  • Routings are intuitive, since the busbar has a similar form to the space that it is installed into.
  • Simplifies builder training / onboarding
  • Cables are often disregarded in 3D models, and cause build issues or inconsistencies.
  • Concerns can be reduced by implementing processes, like including cables in 3D models, build instruction with pictures and video, and builder training.
9 Quality Control, Component
  • Few conductivity concerns, since worskmanship and process changes do not greatly affect terminal resistance.
  • Busbars with tin plating have fewer installation problems, as builders do not need to polish the busbars to remove copper oxidation.
  • Crimping tooling and process changes result in quality varinces.
  • Visual quality control checks may not discover terminal resistance issues.
  • Actual terminal resistance checks are possible, but require tooling, and become another build worstation / process.
  • Terminal resistance quality control checks may not discover conductor-opens, related to vibration issues.
10 Quality Assurance, System
  • More consistent product due to component quality control, and fewer build errors.
  • More quality control issues due to incorrect routing paths and incorrect fastener torques.
  • Issues can be reduced by including dedicated cable tie locations in the design.
  • Issues can be reduced by using push-to-lock terminals, such as Anderson Power Products SB175
11 Material Cost
  • Short lengths with few bends are often less expensive than cables.
  • Often more expensive than a similar busbar.
  • Cables become the lower cost option when using long lengths.
  • Cables become the lower cost option when 3D forms are complex, since cable bends do not have a material or process cost.
12 Item Number Markings
  • Heat shrink label.
  • Laser etching the copper.
  • Stamping or engraving the copper.
  • Heat shrink label.
13 Colour Coating
  • Heat shrink tubing.
  • Powder coating.
  • Cable's insulating jacket colour.
  • Heat shrink tubing.
14 Oxidation
  • Bare copper joints need polishing before installation, to remove surface oxidation that has a high electrical resistance.
  • Busbar can be plated to reduce oxidation concerns.
    Silver, tin, nickel, and gold are plating options.
    1 metre lengths of plated busbars are available from compaines like Phoenix Contact, WAGO, and WeidmĂĽller. Refer to Phoenix Contact's 0402006 as an example of a copper busbar with tin plating.
  • Jacketed cables are available with plain copper strands, or with plated copper. Plating can reduce oxidation issues in areas exposed to air.
  • Crimped terminals will exclude air from electical joint.
  • Adhesive heat shrink tubing near the crimp can exclude air from the conductors inside the cable's jacket.
  • Solder flux should be washed off, since flux is hygroscopic, and will increase the rate of oxidation.
15 Operating Temperature
  • Busbars with a powder coating or heat shrink tube have similar limitations to cables.
  • Most cables are limited to an operating temperature of 90°C due to the insulation jacket material. Refer to the cable manufacturer's datasheet, since some cables have a higher acceptable operating temperature.