In short
- Cable wins at low currents and short runs and where the route must adapt on site.
- Busbar wins above about 800 A, on long runs and where loads will be added or moved.
- A 2,000 A feeder in cable typically needs several parallel conductors per phase; busbar does it in one housing.
- Busbar is a type-tested assembly (IEC 61439-6); a cable route is verified by calculation and workmanship.
- Decide early: busbar routes and fittings are fixed in design, not on site.
Where the crossover sits
The cost of cable rises almost linearly with current: double the current, double the copper and the number of pulls and terminations. Busbar has a higher entry price per metre but scales better, because one housing carries the whole current. The two usually meet somewhere around 800 A; above that, and especially over long distances, busbar tends to be cheaper installed.
Side by side
| Criterion | Busbar trunking | Parallel cables |
|---|---|---|
| Installation | Prefabricated lengths bolted together; few site terminations | Many pulls and terminations; time grows with cable count |
| Space | One compact housing | Wide trays or ladders; bending radius governs |
| Changes | Plug-in tap-offs along the run | New circuit back to the board |
| Verification | Type-tested assembly (IEC 61439-6 / UL 857) | Design calculation and installation practice |
| Route | Fixed fittings; plan early | Easy to adapt on site |
| Upfront cost | Higher at low currents; competitive at high currents and long runs | Lower at low currents and short runs |
Space and installation time
A 2,000 A feeder in single-core cable typically needs five or more parallel conductors per phase once grouping derating is applied, plus neutral and earth: dozens of cables on wide ladders, each pulled, cut, glanded and terminated. The same feeder in busbar is one housing a few hundred millimetres wide, bolted length by length.
On a data center programme, fewer terminations mean fewer hours on the critical path, fewer torque checks and fewer points for a hot joint.
Change and growth
This is where busbar earns its place in white space. Track busway above the racks lets you plug a tap-off in wherever a rack lands, change its rating when the rack changes, and avoid running a new cable from the PDU for every move. With AI racks changing every hardware generation, that flexibility is worth more than the metal.
Size a whole row of tap-offs in the run builder.
Fire load and magnetic fields
- Fire load: busbar uses far less combustible insulation than the equivalent bank of cables, which lowers fire load and smoke in the route. Fire barriers keep wall and floor ratings where the run passes through.
- Magnetic fields: in sandwich designs the phases sit close together, so their fields largely cancel. Large cable bundles laid loosely produce stronger stray fields.
Comparing cost properly
Compare installed cost, not material price: include trays and supports, labour for pulls and terminations, testing, the space the route takes, and the losses over the life of the run. With copper at record prices, the conductor metal itself is now a large line; an aluminium busbar can change the comparison. Price both metals in the copper desk.
A checklist for your project
- Is the design current above about 800 A, or the run longer than a few tens of metres?
- Will loads be added, moved or re-rated during the life of the building?
- Is the route fixed early enough to order fittings?
- Is there space for wide cable ladders, or is the ceiling crowded?
- Does the programme reward fewer site terminations?
Three or more "yes" answers usually point to busbar.
Questions about busbar vs cable
Is busbar always more expensive than cable?
Per metre at low currents, yes. At high currents and on long runs, the installed cost is often lower because one housing replaces many cables, pulls and terminations.
Can busbar follow a complex route?
Yes, with elbows, tees and offsets, but each fitting is made to measure. The route must be fixed in design; late changes cost time.
Which is better for AI racks?
Overhead track busway, because tap-offs can be added or re-rated as racks change, without new cables back to the PDU.
Sources
- IEC 61439-6 (busbar trunking systems); IEC 60364-5-52 (cable selection and grouping).
- UL 857, Busways; NEC Article 368.
- Comparison reflects common industry practice; costs vary by market and project.