How to choose busbar trunking: a buyer's guide for consultants and contractors
Selecting busbar trunking for a project means weighing current rating, voltage drop, ambient, IP rating and standards. Here's a practical 8-step checklist used on real GCC and MENA projects.
Al Sanaya Engineering
·9 min read
If you're specifying busbar trunking for a high-rise tower, an industrial plant, a hospital or a data centre in the GCC, the technical decisions you make in the first design week will shape installation, lead-time and total cost for the rest of the project. Below is the 8-step framework we walk through with consultants and contractors before issuing a quote.
1. Establish the load profile
Start with the total connected load, the diversity factor, and the projected growth over the building's first 5 years. A residential tower's load profile is fundamentally different from a hospital or a data centre, and the right busduct rating follows from that profile — not from a generic per-floor estimate.
2. Calculate continuous current with derating
Catalogue current ratings assume a 35°C ambient. In the GCC, plant rooms can run at 45–50°C in summer. Apply the manufacturer's ambient correction table (typically 5–8% derating for every 5°C above the reference) before sizing the rating.
3. Verify short-circuit withstand
The busduct's peak (Ipk) and 1-second (Icw) withstand ratings must match or exceed the upstream switchgear's prospective short-circuit current. This is a non-negotiable safety requirement and the first item an authority having jurisdiction will check.
4. Run the voltage-drop calculation
Voltage drop frequently dictates the conductor size on long feeders, particularly rising mains above 30 m. Sandwich-type busduct typically delivers 30–50% lower per-metre drop than equivalent cable — but the calculation should be project-specific, not a rule of thumb.
5. Confirm fire and IP requirements
Decide IP40 vs IP54 vs IP66 by the actual installation environment, not by default. Higher IP slows convective cooling, which compounds the ambient derating. For floor penetrations, fire-retardant ratings to IEC 60331 are the regional standard.
6. Plan the route and tap-offs
Walk the shaft drawing with the busduct cross-section overlaid. Tap-off boxes should be placed where electrical schematics call for them — not where the contractor finds it convenient on site.
7. Specify standards and test reports
- IEC 61439-1 and IEC 61439-6 (busbar trunking)
- KEMA, ASTA or UL design verification report
- IEC 60331 fire integrity (where applicable)
- Manufacturer-issued type test report — not just a self-declaration
8. Commercial evaluation
When all four major manufacturers technically comply, the deciding factors come down to lead time, regional inventory, after-sales support and the supplier's track record on similar GCC projects. We supply both Linkk and Megaduct from regional inventory, and we'll let the engineering team make the call on which fits best for the brief.
Frequently asked questions
What is busbar trunking used for?
Busbar trunking — also called busduct or busway — is used to distribute electrical power from a substation or main switchgear to multiple loads along a defined route. It is most common on rising mains in tall buildings, horizontal feeders in industrial plants, and distribution within data centres.
What current ratings are available?
Sandwich-type busbar trunking is typically available from around 250 A up to 6300 A in standard catalogue ratings. Beyond that, custom configurations are possible. For GCC ambient conditions, ratings should be derated using the manufacturer's correction tables.
Is copper or aluminium better for busduct?
Copper offers lower resistivity and a smaller cross-section for the same current — ideal for tight shafts. Aluminium is lighter and lower-cost for equivalent current rating. The choice depends on shaft space, total cost of ownership, and fault-current requirements.
Which standards should busbar trunking comply with?
IEC 61439-1 (general rules) and IEC 61439-6 (busbar trunking systems) are the primary standards. Independent KEMA, ASTA or UL test reports demonstrate compliance with design verification requirements.
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