Busway (Busduct)

Busway (also called busduct) is a prefabricated, modular power-distribution system in which solid copper or aluminum conductors — busbars — run inside a grounded metal housing. Instead of pulling individual cables in conduit from a panelboard to every rack, a facility runs busway overhead and taps power off it wherever needed. In North America it is governed by UL 857, and it has become the default distribution approach for high-density mining halls and data centers, where the ability to add and move circuits quickly is worth real money.

Plug-in and tap-off architecture

The defining feature is drawing power anywhere along the run. Plug-in busway provides tap-off windows at fixed intervals; a plug-in unit containing breakers or fuses clips onto the window and feeds a power whip down to a rack PDU. Open-channel or "track" busway goes further, offering a continuous slot so tap-off units can be added or repositioned at any point along the length — in many designs without de-energizing the run, so a new rack row comes online while its neighbors keep hashing. Feed types round out the system: end-feeds and center-feeds bring power onto the bus from switchgear, and elbows, tees, and expansion joints route it through real buildings.

Why mining halls prefer it

Compared with conduit-and-cable, busway is faster to install, more compact, and dramatically more adaptable: adding a circuit means clipping on a tap unit rather than pulling new wire all the way back to a panel. In a mining facility where machine generations turn over every couple of years — and where each generation changes the per-rack power density — that repositionability cuts both electrician cost and downtime. The enclosed busbars also carry very high currents in a small cross-section with excellent heat dissipation, which suits the dense, continuous, three-phase loads of an ASIC hall better than bundles of large-gauge cable in crowded tray. Monitoring integrates cleanly too: modern tap-off units often carry metering per drop, giving the operator circuit-level visibility across the floor.

Trade-offs and planning

Busway carries a higher up-front material cost than cable, and it rewards planning: the run's route, ampacity, and tap spacing are chosen once and constrain everything after. Ratings must anticipate the densest hardware you might deploy, not just today's, since replacing an undersized bus is far more disruptive than upsizing a cable would have been. Joints and tap connections are the maintenance points — they should be torque-checked and thermally scanned on schedule, because a degraded high-current joint fails hot. For long, fixed, low-change installations, conventional cabling can still win on cost; busway earns its premium where change is the norm.

Position in the distribution chain

Ratings span a wide range — feeder and plug-in busway is commonly built from a few hundred amps to several thousand — and the conductor choice inside is its own trade: copper carries more current in a smaller section, while aluminum saves weight and cost for the same ampacity at a larger size. Voltage ratings comfortably cover the 208–600 V classes a mining facility uses. The discipline that matters at design time is headroom: a bus sized to today's fleet at 80% becomes tomorrow's bottleneck after one efficiency generation, so experienced builders size the spine for the building's electrical service, not for the current machines.

Busway occupies the middle of the facility's power path: switchgear and transformers feed the bus, the bus feeds tap-offs, tap-offs feed whips and rack PDUs, and the PDUs feed individual machines through couplers like the IEC 60320 C19 / C20. Upstream is built to change rarely; downstream churns with every hardware refresh. Busway is what lets the two coexist.