Data centre
Busbar trunking and busway
Busbar trunking, called busway in the US, runs over rack rows with plug in tap off units and in risers and transformer links, specified by current, conductor and route.
- Rated current
- A, per run
- Conductor
- copper or aluminium
- Use
- rack rows, riser, transformer link
- Tap offs
- number and ratingfor rack rows
- Standard
- IEC 61439-6busbar trunking systems
Over a rack row, busway replaces a run of cables with one track and plug in tap off units, so a rack can be powered or moved without a shutdown. In a riser or between a transformer and its main switchboard, busbar trunking carries currents that would take many parallel cables.
The route is the specification: straight lengths, elbows, the feed unit and every tap off with its rating and protection.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Rated current | 160 A to 6300 A | The load per run |
| Conductor | Copper or aluminium | Weight, size and cost |
| Voltage and system | 400 V, 3 phase with neutral and earth | The board it is fed from |
| Degree of protection | IP54 or IP55 for risers; lower for overhead runs | The space it runs through |
| Tap off units | Number, rating, protection, metering | The racks or loads served |
| Short circuit rating | kA for a stated duration | The fault level |
A busway run
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 61439-6 | Low voltage switchgear and controlgear assemblies, busbar trunking systems |
| BS EN 61439-6:2012 | The current GB edition, Busbar trunking systems (busways), designated by BSI; a revised edition exists only in draft |
| BS 8519:2020 | Fire resistant power and control cable systems for life safety and fire fighting, code of practice |
Fire rules in a UK building
Since the 18th edition, regulation 521.10.202 of BS 7671 requires wiring systems throughout an installation to be supported so they will not collapse early in a fire; the IET gives the purpose as keeping hanging wiring from hindering evacuation and firefighters. BEAMA's guide reads the BS 7671 definition of a wiring system as including busbars, so a busway's hangers are part of that question.
Where a run feeds life safety or fire fighting equipment, BS 8519:2020 is the code of practice for fire resistant power and control cable systems. BSI's description does not say whether it covers busbar systems, so ask the maker for evidence of fire integrity for the system offered. Where the run passes through a fire separating wall or floor, Approved Document B asks for the opening to be fire stopped.
What we need to quote
- Use: rack rows, riser or transformer link
- Rated current and voltage
- Route with lengths, elbows and the feed point
- Number and rating of tap off units, and their protection
- Fault level and degree of protection
- Destination and the date required on site
Building or expanding a facility?
Send the whole equipment schedule as one project, each item with its own requirements.