Busbar Trunking or Cable? Choosing the Right Distribution Method
For high-current distribution, the choice between busbar trunking and cable is about flexibility as much as cost.
ContentsBusbar trunking carries conductors inside a metal housing and allows power to be tapped off at chosen points along its length. On high-current main runs it is considered as an alternative to a large number of parallel cables, although it does not suit every installation.
Components of the system
A trunking run is assembled from standard parts joined together. This modularity is the source of its most distinctive advantage.
When is trunking the better choice?
Above roughly 1000 A, a cable solution requires many parallel conductors. That means wider trays, more lugs, larger terminal volumes and considerable installation labour. Trunking saves space at this point and shortens installation time. Its second major advantage is flexibility: when a production line changes, a tap-off box can be relocated to supply the new machine, with no new cable pull required.
A side-by-side comparison
The decision should rest on the lifetime scenario of the facility rather than on a single criterion.
| Criterion | Busbar trunking | Cable |
|---|---|---|
| Space at high current | Less | Grows with parallel runs |
| Later modification | Easy via tap-off box | Requires a new run |
| Initial investment | Usually higher | Usually lower |
| Installation time | Short, modular | Long, labour intensive |
| Short-circuit withstand | High, defined Icw | Depends on cable and installation |
| Fire load | Low | Depends on insulation material |
| Fault location | Fast, section by section | Time consuming along the run |
Points to watch in design
Choosing trunking raises decisions that sit outside the panel yet connect directly to it:
- The adapter at the panel outlet must match the assembly’s short-circuit rating
- Heating differs on horizontal and vertical runs, so derating factors are assessed separately
- Expansion units must be planned for building movement
- Suitable barriers are used where the run crosses fire compartments
- Tap-off boxes should sit at a height that allows maintenance
The same heating logic applies to busbars inside the panel; see busbar ampacity and derating. For the conductor material decision, the copper versus aluminium comparison is a useful guide.
Key takeaways: busbar trunking
- Components of the system — A trunking run is assembled from standard parts joined together.
- When is trunking the better choice — Above roughly 1000 A, a cable solution requires many parallel conductors.
- A side-by-side comparison — The decision should rest on the lifetime scenario of the facility rather than on a single criterion.
- Points to watch in design — Choosing trunking raises decisions that sit outside the panel yet connect directly to it:
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
Is trunking always more expensive?
On initial investment usually yes, but total cost can differ. Once many parallel cables, trays, lugs and installation labour are added, the gap narrows, and once later modifications are considered trunking can come out ahead.
Can a tap-off box be fitted to a live run?
Some systems support this, but it depends on the manufacturer’s procedure and on authorised personnel. Leaving room for de-energised installation is the safer design approach.
Where does cable make more sense?
Where currents are modest, the route is complex and full of changes in direction, or the layout will stay unchanged for many years, cable is both more adaptable and more economical.
Related articles
- Busbar Current Carrying Capacity and Derating Calculation
- Cable Sizing and Voltage Drop Calculation
- Busbar Systems: Copper or Aluminium? Selection Criteria
- All technical articles
Devpan designs main distribution assemblies with different outgoing arrangements for trunking and for cable connection. Share your site layout and we will assess both options with you.
