Busbar or Cable? Choosing the Right Factory Power Distribution System and Installing Busbar Trunking

A busbar trunking system (also called a busway) is a prefabricated low-voltage distribution system in which copper or aluminum conductors are enclosed in a metal housing and supplied as factory-built modules that carry power and distribute it along the run. With cable distribution, a separate cable is pulled from the panel to every load; with busbar trunking, power is taken from a single backbone by plugging a tap-off box into the run wherever it is needed. The core product standard for these systems is IEC 61439-6, applied together with IEC 61439-1.

In practice there are two main applications: feeder busbars that carry high current between the transformer and the main LV switchboard, and distribution busbars that deliver power to machines along the production floor. Low-current lighting busbars are a separate product family. With a cable-and-tray system, the route, tray run, joints and terminations are all built on site, so design flexibility is high but the level of prefabrication is low.

Busbar trunking stands out against cable for three reasons: it carries high current in a compact cross-section, its factory-tested modules shorten installation time on site, and it removes the need to pull a dedicated cable back to the panel for every new load. The trade-off is that modules are made to measure, so the route must be finalized before manufacturing, and last-minute site changes are harder to absorb than with cable.

Busbar trunking usually makes more sense where currents are high, many loads are lined up along a run and the machine layout changes often; cable and tray is usually the better fit for a few scattered loads, low-to-medium currents and complex routes. The decision rarely rests on a single criterion. It comes from weighing several together, and below are the criteria we look at most often as a contractor.

Load density: when many consumers sit on the same run, busbar trunking cuts the number of cables dramatically. Frequency of layout changes: if the production layout changes often, relocating a tap-off box is far faster than pulling a new cable from the panel. Ceiling height and supporting structure: busbar is a heavy system, so hanger points, roof and steel structure capacity, and obstacles such as overhead crane runways must be checked in advance.

Fire and environment: busbar trunking can present a lower fire load than many parallel cables, but fire barriers at wall and floor penetrations still need to be planned separately. In humid, chemically aggressive or outdoor environments, suitably sheathed cable is often more practical, and underground and yard routes are cable territory anyway. For a run that feeds only a few machines and will not change, a busbar investment is usually unnecessary.

The main cost drivers of busbar trunking are rated current, conductor material (copper or aluminum), IP rating, run length, special components such as elbows and expansion units, and the number of tap-off boxes and the protective devices inside them. On the cable-and-tray side, cost is driven by conductor size and the number of parallel runs, tray type, pulling and termination labor, and the derating applied to current-carrying capacity because of cable grouping.

As a general rule, cable is the more economical initial investment at low and medium currents on simple routes. As current rises and more loads hang off the run, the number of parallel cables, tray width and labor grow quickly; at that point the total installed cost of busbar trunking can approach or even fall below that of cable. The comparison should never rest on material prices alone. It must also account for installation time, voltage drop, future layout changes and maintenance costs.

Because unit prices move quickly with metal prices and exchange rates, quoting a fixed figure would be misleading. A sound comparison comes from pricing both alternatives on a quantity takeoff built from a site survey and the load list.

The three most critical points in busbar installation are torquing module joints to the manufacturer's values, accommodating thermal expansion with expansion units and the correct hanger arrangement, and maintaining the IP rating with flange and cover kits that suit the mounting orientation. Installation should begin with a route drawing based on as-built site measurements, and modules should be stored in a covered, dry area once they arrive on site.

At each joint, contact surfaces must be clean, phase sequence and module orientation must be verified against the markings, and bolts must be tightened with a calibrated torque wrench. Many systems use shear-head bolts that snap off once the specified torque is reached; even then, every joint should be marked and recorded. A loose joint is the most common cause of overheating, and eventually failure, on a busbar run.

If expansion units are left out on long straight runs and at building expansion joints, thermal elongation of the conductors strains the joints and hangers, which is why spring hangers are used between floors on vertical risers. On many products the IP rating depends on mounting orientation (edgewise, flat or vertical) and on fitting the joint flange and cover kits in full, so the catalog value should always be checked against the actual mounting position. Unused tap-off openings must be closed, joint covers fully fitted and fire barriers installed at wall penetrations. The run should not be energized until insulation resistance, phase sequence and protective conductor continuity have been verified.

A busbar run connects to the transformer and the LV switchboard through flanged end units made to the equipment's connection dimensions, combined with flexible connectors. Flexible copper connections on the transformer side keep the transformer's vibration and thermal movement from being transmitted into the run, which is why rigid direct connections are avoided.

For a sound connection, transformer bushing spacing, connection height, phase sequence and neutral position must be coordinated between the busbar manufacturer and the transformer and switchboard manufacturers before production. For example, a 1,600 kVA transformer has a rated current of roughly 2,300 A on its 400 V side. Carrying that current by cable takes many parallel cables per phase, whereas a single feeder busbar offers a much tidier solution.

The busbar's rated current and short-circuit withstand rating must be matched to the transformer's rated current and the prospective short-circuit current, and the main circuit breaker's protection settings must be coordinated accordingly. In facilities with heavy harmonic loads, the neutral conductor size should be assessed separately; some products offer an oversized neutral option.

In most cases, yes: the changeover is done by installing the new busbar run in parallel while the existing cables stay in service, then transferring loads in groups during short, planned outages. Truly zero downtime is rarely possible, so the goal is to align outages with shift changes, weekends or scheduled maintenance shutdowns.

The typical sequence is: carry out a site survey and compile the load list, select a route that minimizes impact on production, install the supports and the run while de-energized, feed and test the run from a spare or new outgoing feeder, and then move machines one by one to the new tap-off boxes. A lockout/tagout (LOTO) procedure must be applied at every transfer step, and old cables should only be removed once all loads have been transferred.

Because the work involves working at height above production areas, the health and safety plan should be prepared jointly with machine operators and the maintenance team. Changeovers like this run more predictably under a turnkey model in which design, manufacturing and site execution sit with the same team; we cover that model in detail in our article "The Single Technical Point of Contact Model in Turnkey Electrical Contracting."

Busbar joints and tap-off boxes need periodic inspection and on-load thermal imaging because load cycles, temperature cycles and vibration can loosen them over time. A loosened joint heats up as contact resistance rises; if it goes unnoticed, it ages the insulation and can escalate into an arc fault.

Thermal imaging surveys should be carried out while the run is under a significant, representative load, comparing temperature differences between phases and between similar joints. During planned shutdowns, torque checks per the manufacturer's instructions, insulation resistance measurement, dust cleaning and inspection of the protective devices in the tap-off boxes are carried out. Recording results at the same points every year reveals degradation trends that a single measurement cannot show.

On factory electrical projects across Türkiye, Miratek Elektrik evaluates busbar and cable alternatives against each project's load profile and layout, and delivers LV panel manufacturing, busbar installation, testing and commissioning in a single workflow. Our work at Pekintaş's factory in Düzce, where we designed the busbar power distribution system, installed the busbar runs and tap-off modules, and then tested and commissioned the system, is one field example of this approach. If you are planning a new production line or a capacity expansion, the right method can be defined together through a site survey and your load list.