Frequently Asked Questions

Technical Overview
 

Cable Bus Fundamentals

What is cable bus?

Cable bus is a high-current power feeder system consisting of insulated power conductors installed inside a ventilated metal enclosure. The enclosure maintains conductor positioning and spacing while allowing airflow around the conductors.  

Unlike traditional busway, which carries current through rigid bus bars, cable bus carries power through insulated cables.  

Why are the conductors installed in a ventilated enclosure?

Ventilation allows air to circulate around the conductors and dissipate heat. This enables cable bus to take advantage of free-air conductor ampacity where permitted by the applicable code, conductor rating and connected equipment.  

Both Cablofil Cable Bus and Power Bus Way apply this free-air principle, using slotted enclosures to support airflow and heat dissipation. Both systems can be configured for free-air ampacity ratings or derated to meet specific project requirements. 

Does free-air ampacity apply to the entire electrical connection?

Not automatically. 

The allowable ampacity of a cable bus system can also be limited by the temperature rating and listing requirements of the equipment at each termination. For example, NEC 110.14(C) affects conductor sizing at low-voltage equipment terminations.  

Legrand recommends evaluating the entire system – from source equipment, through indoor and outdoor cable bus routing, to the load equipment –- rather than applying a free-air ampacity value to every portion of the circuit without considering termination limitations.  

Please contact us so we can discuss your project and determine the configuration of your cable bus system.

Why can cable bus use fewer conductors than some conventional feeder systems?

Cable bus can use fewer conductors than some conventional feeder systems because properly spaced conductors operating in free air can dissipate heat efficiently. A cable bus design may require fewer parallel conductors than an installation where the same conductors are grouped in conduit or another installation condition.  

The actual conductor count must be determined for the specific system based on current, voltage, conductor material and size, ambient temperature, equipment termination ratings, applicable codes and other engineering requirements.  

Electrical Ratings & Performance

What are the voltage ratings of Legrand’s cable bus systems?

Cablofil Cable Bus: Up to 600v.  

Power Bus Way Cable Bus: Up to 69kV, allowing it to address low- and medium- voltage applications as well as higher-voltage project requirements.  

What ampacities are available?

Cablofil Cable Bus: 2,000A - 6,000A. 

Power Bus Way systems can be engineered for currents up to 8,000A.  

Final system sizing depends on the complete electrical application rather than the cable bus rating alone.  

What is the short-circuit rating?

A short-circuit rating, also called a withstand rating, indicates a system’s ability to withstand the intense forces generated during an electrical fault. These forces can reach thousands of pounds. Withstanding them helps reduce the risk of injury and equipment damage and supports timely inspection and safe re-energization after the fault has been resolved. 

Cablofil Cable Bus has been short-circuit tested and UL tested to 125,000A RMS. 

Power Bus Way systems can be designed with a short-circuit rating up to 200kA, depending on the system configuration. 

Why is short-circuit performance important in cable bus?

During a fault, conductors can experience extremely high electromagnetic forces. A cable bus system must maintain conductor spacing and mechanically restrain the cables during those events.  

Both Legrand systems use engineered cable support blocks to hold conductors in position. The HDPE blocks for Cablofil Cable Bus are designed to prevent cable movement and contain conductors during a fault condition. Power Bus Way uses V0 flame-rated GPO-3 support blocks designed to support the conductors during short-circuit events.  

Can the cable bus systems use copper or aluminum conductors?

Power Bus Way and Cablofil supports both copper and aluminum conductors.  

For U.S. applications, available cable types include XHHW-2, RHH/RHW-2 and MV-105, with cable sizes available up to 1,000kcmil. 

Conductor requirements for Legrand Cable Bus should be determined as part of the project design to ensure safety and lowest installed cost.  

Can the cable bus systems support a neutral conductor?

Power Bus Way can be configured for three-phase or three-wire, four-wire AC systems, allowing the system to accommodate applications requiring a neutral. It can also accommodate two-pole or one-pole DC configurations.  

Cablofil Cable Bus  can be configured for three-phase or three-wire, four-wire AC systems, allowing the system to accommodate applications requiring a neutral. 

Construction

What is the cable bus enclosure made from?

Power Bus Way Cable Bus uses 6061-T6 aluminum side rails and stainless steel hardware. Its standard technical options include aluminum and stainless steel enclosures, with painted options also available.

Cablofil Cable Bus is constructed using 6063-T6 aluminum side rails and stainless steel hardware.

How large can a Power Bus Way enclosure be?

Power Bus Way and Cablofil creates enclosures up to 12 inches high by 36 inches wide. The required dimensions depend on conductor count, cable size, electrical characteristics and routing requirements.  

How are the conductors secured?

In Power Bus Way systems, conductors are supported by block-style cable supports positioned at a maximum spacing of 36 inches. The blocks use V0 flame-rated GPO-3 material. 

Cablofil Cable Bus uses high-strength V0 HDPE cable spacing blocks with a patented hold-down bar. The blocks maintain required air spacing and restrain cable movement without requiring through- or cross-bolts. 

Does the enclosure carry the electrical load?

No. The insulated conductors carry the electrical current. The cable bus enclosure provides the mechanical pathway, protection, ventilation, cable spacing and structural support required for the system.  

How is the enclosure bonded?

Power Bus Way provides bond cables with its cable bus systems to establish a continuous grounding path and minimize potential voltage differences between enclosure components.  

Bonding and grounding for any cable bus installation must follow the engineered system requirements and applicable electrical codes.  

Routing & Fittings

Can Legrand’s cable bus systems accommodate change in direction?

Yes. Both systems are designed to accommodate project routing.  

Cablofil Cable Bus offers 12-inch and 24-inch fitting radi, including configurations in standard horizontal and vertical changes of 30, 45, 60 and 90 degrees. Cablofil Cable Bus also offers adjustable splices that allow for directional changes other than the standard changes. 

Power Bus Way can provide straight sections as well as project-specific fittings such as horizontal and vertical routing components, orientation-change fittings, transition fittings, reducers and T-fittings.  

What is an orientation-change fitting?

Power Bus Way’s Orientation Change Fitting (OCF) allows the cable bus system to rotate from one axis to another without requiring a combination of conventional horizontal and vertical 90-degree fittings.  

This can reduce the number of components required and help accommodate equipment interfaces or space-constrained routing.  

Can multiple cable bus circuits share an enclosure?

Power Bus Way can incorporate a T-Fitting that allows more than one cable bus system to share an enclosure for part of a route before terminating at different locations.  

Can the enclosure size change along the route?

Power Bus Way offers expansion/reducer fittings that transition between different enclosure dimensions when additional or reduced cable space is needed.  

What happens if field dimensions change after Cablofil Cable Bus is ordered? 

Field adjustability is one of the primary design advantages of Cablofil Cable Bus.  

The modular system allows contractors to make certain pathway modifications and fabricate sections in the field instead of requiring every section to arrive as a fixed, project-specific assembly. An extra-long adjustable gap-filler splice is also available to accommodate dimensional adjustments without additional tray cutting.  

Equipment Connections & Terminations

How does cable bus connect to transformers, switchgear or other electrical equipment?

The conductors ultimately terminate at the connected equipment using the appropriate electrical termination method, while the cable bus enclosure interfaces with the equipment through engineered entrance or termination components.  

Power Bus Way can provide equipment flanges, termination flanges, transition flanges, compression lugs, termination kits and other accessories as part of the engineered system.  

Cablofil Cable Bus has equipment entrance solutions designed to transition the pathway into the connected equipment.  

How does Power Bus Way accommodate equipment with unusual termination geometry?

Because Power Bus Way is engineered for the specific product, its enclosure, fittings and equipment interfaces can be designed around actual equipment locations and termination requirements.  

Transition flanges, orientation-change fittings and reducer fittings can be used where equipment geometry requires a different enclosure size, cable arrangement or entry orientation.  

Do cable bus conductors require splices along the run?

A key advantage of a cable bus system is the ability to use continuous insulated conductors from termination to termination, reducing intermediate electrical connections.  

Power Bus Way specifically designs its systems around continuous end-to-end cable, and Cablofil Cable Bus also uses insulated conductors with fewer terminations.  

Applications

Can Legrand cable bus systems be installed outdoors?

Yes. Both Legrand cable bus solutions can support outdoor installations. Cablofil offers weatherproof equipment entrances and an IP67-rated wall plate designed to protect wall penetrations against dust and water.  

Power Bus Way offers IP66 connectors at equipment interfaces and uses materials and hardware designed for indoor and outdoor environments.  

What ambient temperature can Power Bus Way accommodate?

Power Bus Way lists an operating ambient range of -40°C to 60°C (-40°F to 140°F).  

Actual conductor ampacity must still account for the ambient conditions along the cable bus route.  

Does cable bus require heaters or blowers for cooling?

Power Bus Way does not require heaters or blowers to maintain operating temperature. Its ventilated enclosure supports passive airflow around the conductors.  

Can the cable bus systems be installed underground?

Power Bus Way offers underground cable bus configurations using precast or cast-in-place systems, with pedestrian- or heavy-traffic-grade options and ventilated or non-ventilated configurations depending on project requirements. 

Wall & Floor Penetrations

How do the Legrand cable bus systems pass through an exterior wall?

Cablofil offers a watertight IP67 facility entrance wall plate for building penetrations as well as a weatherproof equipment entrance.  

Power Bus Way offers wall penetration flanges that allow the cable bus enclosure to terminate directly against brick, panel or corrugated wall construction. 

Can Legrand cable bus systems penetrate a fire-rated wall or floor?

Yes, when the appropriate engineered firestop assembly is used.  

Power Bus Way offers integrated firestop solutions for cable bus penetrations, including systems using fire-rated bricks and sealants that meet standards including UL 1479, CAN/ULC-S115 and ASTM E814, with configurations available for fire ratings up to four hours.  

The firestop assembly must be selected and installed for the specific rated construction and project requirements.   

Codes, Standards & Certifications

What codes and standards apply to Cablofil Cable Bus?

Cablofil Cable Bus is:

• Certified to NEMA Standard 15000 for cable bus systems. 
• Short-circuit tested and UL tested to 125,000A RMS. 
• Designed to meet NEC requirements for free-air conductor ratings.  

What codes and certifications apply to Power Bus Way?

For U.S. applications, Power Bus Way is compliant with NFPA 70/NEC Article 370 and NEMA VE-1 requirements.  

In Canada, Power Bus Way identifies certifications including CSA C22.2 No. 273:19 for cable bus, along with Canadian Electrical Code compliance.  

Installation & Supports

How are the Legrand cable bus systems supported?

A cable bus system must be supported along the engineered route.  

Power Bus Way can provide project-specific support structures including wall supports, T-supports, H-supports, cantilever supports, trapeze systems and ground-mounted support configurations. Supports can be manufactured from aluminum or structural steel.  

Cablofil Cable Bus uses a more modular installation approach built around its ladder tray platform and associated support system.  

Does Power Bus Way use external supports?

Yes. External supports can be designed and manufactured as part of the complete cable bus package. 

Is field cutting required?

Depends on the system. 

Cablofil Cable Bus is intentionally designed to allow contractors to make field modifications and fabricate portions of the pathway onsite.  

Power Bus Way Cable Bus follows a custom-engineered approach in which individual system components are designed around the project dimensions before installation. Straight sections and fittings can be uniquely identified to correspond with installation drawings and simplify field assembly.  

Engineering & Project Design

What information is required to design a cable bus system?

Typical project information can include: 

• System voltage 
• Required ampacity 
• AC or DC system 
• Number of phases and wires 
• Neutral requirements 
• Available short-circuit current 
• Conductor material 
• Source equipment 
• Load equipment 
• Equipment termination temperature ratings 
• Equipment locations and connection points 
• Indoor and outdoor ambient temperatures 
• Cable bus routing 
• Building penetrations 
• Environmental conditions 
• Support requirements 
• Applicable electrical codes 
• Project schedule 

Additional information may be required depending on the selected cable bus solution and project complexity.  

Why do equipment termination temperatures matter?

The cable insulation may be capable of operating at a higher temperature than the termination point on the connected equipment.  

For low-voltage U.S. applications, NEC 110.14(C) can therefore affect the allowable conductor ampacity at equipment terminations. A cable bus system must be designed around the complete electrical path, not simply the maximum free-air ampacity of the conductor itself.  

Does ambient temperature affect cable bus sizing?

Yes. The temperature surrounding the conductors can affect allowable ampacity.  

A system routed outdoors through a high-temperature environment may require different ampacity correction considerations than the portion of the same feeder routed through a conditioned electrical room. Those conditions should be evaluated during system engineering.  

Does Power Bus Way provide field measurements?

Yes. Power Bus Way offers field measurement and project services to help confirm dimensions and identify routing or equipment interface issues before manufacturing. For complex projects, 3D field scanning may also be used to improve dimensional accuracy.  

Selecting Cablofil or Power Bus Way

When is Cablofil Cable Bus the best fit?

Cablofil Cable Bus is well-suited for low-voltage AC applications up to 600V where project speed, modularity and contractor control are priorities.  

Its field-adjustable construction can be especially valuable when final dimensions may change during construction or when a project cannot accommodate the engineering and manufacturing timeline of a fully customized system.  

When is Power Bus Way the better fit?

• Currents up to 8,000A 
• Voltages up to 69kV 
• Medium-voltage applications 
• DC configurations 
• Highly customized routing 
• Complex equipment interfaces 
• Underground routing 
• Custom fittings or supports 
• Extensive engineering and field-measurement support 

Is Power Bus Way simply a higher-capacity version of Cablofil Cable Bus?

No.  

The primary difference is not simply ampacity. The two solutions use different project-delivery models. 

Cablofil Cable Bus uses a standardized, modular platform designed to give contractors more hands-on control and field flexibility, along with support for shorter project timelines.  

Power Bus Way is a custom-engineered system in which the route, fittings, supports, equipment interfaces, cables and terminations can be designed as an integrated package for the individual project.  

Can Legrand help determine which cable bus solution is appropriate?

Yes. Because both solutions are part of the Legrand portfolio, the project can be evaluated based on its actual electrical requirements, physical layout, schedule and desired installation approach rather than forcing the application into a single cable bus platform.