Busway vs Cable for Data Center Power Distribution

Architecture

Busway is a prefabricated, enclosed conductor system installed overhead in the data center. Power is distributed along the busway run, and tap-off units connect to the busway at any position along its length to provide a PDU feed at each rack location. The busway run connects to the main distribution board or switchgear at one or both ends.

Cable assemblies route individual power cables from the distribution board or branch circuit panel to each rack PDU. Each cable assembly is a dedicated circuit from the panel to the rack, typically routed through cable trays, conduit, or raised floor.

Installation

Busway installation involves mounting the busway overhead, connecting busway sections, and installing tap-off units at each rack position. The initial installation is more complex than cable, but subsequent rack connections are simple — a tap-off unit is plugged in at the required position without any electrical work.

Cable assembly installation involves routing individual cables from the panel to each rack. For a large data center with many racks, this involves a large number of cables, significant cable management infrastructure, and substantial installation labour. Each new rack requires a new cable run from the panel.

Scalability and Rack Changes

Busway provides high scalability for rack additions and moves. Adding a rack requires only a new tap-off unit at the appropriate busway position — no new cable run from the panel. Moving a rack requires moving the tap-off unit. This makes busway well suited to data centers where rack layout changes frequently.

Cable assemblies require a new cable run for each new rack. Moving a rack may require re-routing the cable or installing a new cable run. In large data centers with frequent rack changes, the labour cost of cable management can be significant.

Power Distribution Flexibility

Busway tap-off units can be positioned at any point along the busway run, providing flexibility in rack placement. The busway current rating determines the total load that can be connected along the run. Individual tap-off units are rated for the PDU feed current.

Cable assemblies provide a dedicated circuit from the panel to each rack, with the circuit rating determined by the cable conductor size and the upstream circuit breaker. Each circuit is independent, which can simplify fault isolation.

Space Considerations

Overhead busway occupies overhead space but frees up floor space and raised floor space that would otherwise be used for cable trays and conduit. In high-density AI data centers where the floor space under and around racks is used for liquid cooling infrastructure (CDU placement, manifold routing), freeing up floor space with overhead busway can be a significant advantage.

Cable assemblies require cable tray or conduit infrastructure for routing, which occupies overhead or under-floor space. In dense deployments, cable management can become complex and restrict airflow.

Maintenance

Busway tap-off units can be replaced or repositioned without de-energising the busway run (depending on the busway design and local electrical regulations). Busway systems require periodic inspection of tap-off unit connections and busway joints.

Cable assemblies require inspection of connectors and cable condition. Replacing a failed cable assembly requires routing a new cable from the panel to the rack.

Monitoring

Both busway and cable distribution systems can be monitored with power metering hardware. Intelligent busway tap-off units with integrated metering provide per-tap power visibility. Separate power meters can be installed at the PDU input for cable-fed racks. The monitoring architecture should be defined as part of the power distribution design.

High-Density AI Rack Considerations

For high-density AI rack deployments, both busway and cable approaches are used. The choice depends on the specific deployment scenario:

• Busway may be preferred where rack layout changes are anticipated, where floor space is constrained by liquid cooling infrastructure, or where the data center will be expanded in phases.
• Cable assemblies may be preferred where the rack layout is fixed, where the distribution board is close to the racks, or where the project budget favours lower initial infrastructure cost.
• Both approaches require high-current rated components for AI rack power levels — confirm busway current rating and tap-off unit rating, or cable conductor size, for the required rack power.
• A+B redundancy can be implemented with either approach — two busway runs or two cable feeds per rack.