Busway and cable tray feeder routes

Busway vs Cable Tray: Choosing a Feeder Method in Ontario

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Busway (also called bus duct) generally suits high-ampacity feeders, tight spaces and buildings where loads will change, while cable tray suits long, irregular routes and lower to moderate currents at a lower material cost. Conduit with wire remains the practical choice for short runs, underground work and low-current circuits. The right answer depends on ampacity, route geometry, expected change and installed cost, and in Canada every option must be designed to the Canadian Electrical Code, Part I (CSA C22.1) as adopted and amended in the province of the project.

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TL;DR

  • Busway packs high current into a compact, prefabricated run and is the fastest to install, but it carries the highest material cost and is the least field-modifiable.
  • Cable in tray costs far less in material, tolerates irregular routing and allows feeders to be moved or reterminated, which suits long runs and moderate ampacity.
  • Conduit and wire has the lowest installed cost in the published comparison below and is the standard answer for short, low-current or underground runs.
  • Busway is covered by CEC Rules 12-2000 to 12-2020, cable tray by Rules 12-2200 to 12-2208, and conduit by Rules 12-1000 to 12-1014.
  • Choose by comparing total installed cost, future tap-off needs and approval requirements on the specific project, not by material price alone.

Table of Contents

What each system is

The three methods are all raceways in the sense of the Code, but they are built and used differently. The CSA C22.1 Handbook, in its discussion of Rule 12-900, describes raceways as channels that enclose and loosely contain conductors, cables or busbars, and lists conduit, wireways, cable trays and busways among the types.

Busway (bus duct). NEMA defines busway as a prefabricated distribution system of bus bars in a protective enclosure, including straight lengths, fittings, devices and accessories, connecting to switchgear, panelboards and transformers. Canadian Consulting Engineer describes it as a modular system in which copper or aluminum busbars sit inside a grounded metal housing, and notes that it performs especially well where amperage is high and loads are tapped off frequently.

Cable tray. A cable tray is an open or partially enclosed support structure that gathers large quantities of cable along main routes. Consulting-Specifying Engineer describes the three methods in these terms, with conduit as a hollow pathway with distance limits and planned pull points, busway as a housing around solid conductors, and tray as the support system for bulk cable.

Conduit, busway and cable tray compared

Conduit. Conduit is an enclosed raceway, usually circular, that gives the conductors a high degree of protection and concealment. It is the baseline against which the other two are compared.

The practical difference is where the engineering happens. With conduit and tray, the conductors are cables assembled on site. With busway, the conductor assembly is a factory-built product, which is why layout must be coordinated early.

Capacity and electrical performance

Ampacity is usually the first filter. Eaton reports that its Canadian Pow-R-Way III low-voltage busway is a 600 V design available from 225 to 5000 A with copper bars, or 225 to 4000 A with aluminum. Medium-voltage non-segregated phase bus duct is used in applications up to 38 kV and 6000 A, with indoor, outdoor and dust-tight environmental ratings available.

Busway also has an electrical advantage. Eaton states that it has a lower voltage drop than cable and conduit because the solid phase bars give lower impedance. On long feeders to remote distribution equipment this can reduce the conductor oversizing that would otherwise be needed.

For cable in tray, capacity is governed by conductor ampacity and derating. Lumera Electric notes that ladder tray with larger conductors is often treated as free air with no derating, while a solid-bottom tray derates like an enclosed raceway. Those assumptions must be confirmed against the applicable Code rules for the project.

At higher currents the tray approach becomes cumbersome. Legrand’s Power Guide states that above about 1000 A, cables can be inappropriate and not cost-effective, cable trays can become technically complicated, and prefabricated busbar systems are more appropriate, whereas trays are more suitable for long lengths of several dozen metres. A supplier source puts the crossover for total cost of ownership at roughly 800 A, or where future flexibility is needed; that is a rule of thumb to test against a real estimate, not a design criterion.

Capacity and electrical performance

Space and routing

Space is where busway earns its price on large feeders. Consulting-Specifying Engineer explains that conduit and wire need at least 60% open space inside the conduits plus spacing between conduits for fasteners. Cable in tray can reduce the overall cross-sectional area, and bus duct allows conductors to be routed close together with minimal insulation and raceway and support requirements.

The trade-off is route complexity. Canadian Consulting Engineer lists complex or irregular routing, constant vibration or movement, and readily available inventory among the reasons cabling may be preferred, while compact design, installation speed and scalability favour busway. Manufacturers have developed elbows and offsets so that busway offers extensive layout versatility, but each fitting is a catalogue item, whereas a tray run follows the structure and cable bends as the site demands.

In practice:

  • Straight vertical risers and electrical rooms to mechanical floors: busway is compact and fast to place.
  • Long horizontal runs across a parking structure or industrial bay: tray is straightforward to hang and extend.
  • Congested ceiling spaces with many crossings: a coordinated model is essential for either, and a prefabricated busway needs it in more detail before it is ordered.

Flexibility and future change

Flexibility is often the deciding factor in multi-tenant and mixed-use buildings. Consulting-Specifying Engineer reports that cable in tray offers some flexibility because feeders can be moved and reterminated, while bus duct offers the most flexibility for future changes, since taps can be added and removed relatively easily.

Eaton’s Busway 101 document adds that new bus plugs can be added, or existing ones swapped for higher-ampacity devices, which is a cost-effective way to adapt. Legrand’s guide notes that prefabricated systems allow connections and disconnections with the power on, which supports continuity of service, and that trunking or tray can be less costly where no modification or maintenance is expected.

The corollary is that busway components are less able to be field modified. The same Consulting-Specifying Engineer comparison observes that designs must be coordinated in relatively high detail, so dimensions, tap-off locations and fittings need to be settled before fabrication. Where future load locations are genuinely unknown, that early coordination is a reasonable price for later flexibility. Where the layout is fixed, it is an unnecessary cost.

Installed cost and lifecycle

Published cost comparisons make the material-versus-labour trade-off concrete. A Consulting-Specifying Engineer case study priced a hypothetical 100-foot, 800 A, 480-volt, three-phase, four-wire feeder in three ways. The figures are in US dollars, reflect the 2022 publication and a US market, and should be treated as a pattern rather than a Canadian quotation.

Method Material Labour Total
Wire in 2.5-inch rigid galvanized conduit $10,800 $11,300 approx. $22,100
Cable in tray $18,100 $4,900 approx. $23,000
Bus duct $62,000 $7,500 approx. $69,500

Source: Consulting-Specifying Engineer cost comparison.

The same publication’s companion article states that bus duct is generally the fastest of the three methods to install, followed by cable in tray and then wire in conduit, that material cost is lowest for wire and conduit and highest for bus duct, and that labour runs the opposite way. Eaton likewise states that installation of cable and conduit is typically more labour-intensive than busway, with the gap widening as the ampere rating rises.

Several points follow for an owner or contractor:

  1. A single 100-foot feeder at 800 A does not favour busway on first cost. The picture changes when the system has many tap-offs, repeated risers or a compressed construction schedule where labour hours and site time carry weight.
  2. Labour rates in Ontario differ from the case study. A local construction cost estimate is the only reliable way to compare the options for a specific building.
  3. Service life is roughly equal. Most designers consider it so, because other system components tend to fail first. Conduit and wire are commodity items that are easy to replace, while bus duct has specific parts that may not be available and may be expensive. Specifying a manufacturer with established Canadian support addresses this.

A detailed electrical construction cost estimation prepared at the design stage allows these options to be priced against the actual layout rather than a generic example.

Where conduit fits

Searches for bus duct versus conduit usually come from the same decision: a feeder that could be run in pipe and wire or as a prefabricated system. Conduit with conductors is better suited where the situation involves low current to a specific source, and conduit is best for underground applications. Conduit also offers the greatest mechanical protection and concealment, and its components are widely stocked.

Busway’s advantage over conduit grows with ampacity. Large feeders in conduit require multiple parallel runs, each with its own conductors, pull boxes and terminations, which is where the labour in the table above accumulates. A busway replaces those parallel runs with one enclosure. For smaller branch wiring, the wiring method decision is different and is discussed in our comparison of MC cable and EMT in Canada.

Conductor material is a related decision that changes the numbers for tray and conduit. Our guide to aluminum versus copper feeders covers code, sizing and cost considerations in Canada.

Canadian Electrical Code requirements

The owner’s brief for any Canadian project is the Canadian Electrical Code, Part I (CSA C22.1), adopted by each province with its own amendments. In Ontario, the Electrical Safety Authority administers the Ontario Electrical Safety Code, and a recent summary lists the 2024 Ontario Electrical Safety Code as the 29th edition, based on the 26th edition of the CEC. The edition and amendments in force on the date of permit application govern the work, so confirm them with the Electrical Safety Authority.

Within Section 12 of the 26th edition, the relevant rules are:

  • Busways and splitters: Rules 12-2000 to 12-2020, covering use, extensions, supports, method of installation, plug-in devices, taps and circuit restrictions.
  • Cable trays: Rules 12-2200 to 12-2208, covering method of installation, insulated conductors and cables, joints and splices, connection to other wiring methods and bonding.
  • Rigid and flexible metal conduit: Rules 12-1000 to 12-1014.

Product standards matter as well. CSA C22.2 No. 201 covers metal-enclosed bus duct rated 751 V to 46 kV, including design, testing and ratings. Equipment installed in Canada should carry the certification required by the authority having jurisdiction.

Environment also constrains choices. The US National Electrical Code, which Canadian practice does not adopt, restricts busway where it is exposed to severe physical damage or corrosive vapours, as reported in an EC&M article. Treat that as an indicator of the questions to ask, and confirm the Canadian rule and the product’s listing and enclosure rating for the actual location, whether indoor, outdoor, sprinkler-proof or dust-tight.

How to choose: a practical sequence

A design engineer typically works through the decision in this order.

  1. Establish the load and the short-circuit duty. Feeder ampacity, voltage drop limits and available fault current set the shortlist. Our power system studies service provides the short-circuit and coordination data these choices depend on.
  2. Map the route. Count the bends, crossings and vertical transitions, and note vibration, moisture and mechanical-damage exposure.
  3. Define the change horizon. Identify tenant fit-outs, EV charging additions, equipment growth or data-hall expansion expected over the building’s life.
  4. Compare installed cost, not material cost. Include labour, schedule, lead time for prefabricated components and spare-part availability.
  5. Verify the Code path. Confirm the applicable rules, product certification and the approval expectations of the local authority having jurisdiction.
  6. Coordinate early. If busway is selected, lock down layout before ordering, since fabricated lengths are less forgiving of field changes.

These rules of thumb summarize the common outcomes:

Project condition Typically favoured
Feeder above roughly 800 to 1000 A, compact shaft or riser Busway
Many future tap-offs, tenant changes, data-centre style expansion Busway
Long, irregular horizontal runs at moderate ampacity Cable tray
Short run, low current, underground or exposed to damage Conduit and wire
Fixed layout with no expected modification Tray or conduit, on cost

Buildings with dense, growing loads, such as a server room or a multi-unit residential tower, usually push toward busway on risers and tray or conduit on laterals. Our guide to electrical safety requirements for multi-unit buildings covers the related life safety expectations.

Our perspective

In our work on Ontario residential and commercial buildings, the feeder method is rarely a question of which product is best in general. It is a question of which one fits the load profile, the architecture and the schedule of one building.

We design power distribution from the service entrance to the panelboards, and we prepare the stamped drawings and the electrical construction cost estimate together, so that busway, tray and conduit can be priced against the same layout before the decision is fixed. That sequence prevents an expensive prefabricated system from being specified where tray would serve, and it prevents a tray run being chosen where a riser busway would save shaft space and site labour.

Our approach is to bring field experience from both new builds and renovations into the design, to coordinate the electrical route with mechanical and structural trades early, and to document the Code basis on the drawings so that permit review proceeds without avoidable questions. For clients with a compressed schedule, we treat the lead time of prefabricated components as a design input rather than a surprise.

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FutureGen Consulting Inc. provides mechanical and electrical engineering design for residential and commercial projects in Ontario, including power distribution, power system studies, emergency power, EV charger infrastructure and electrical construction cost estimation, with permit-ready, engineer-stamped drawings and Code compliance.

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If you are comparing busway, cable tray and conduit for a building, our power distribution design team can size the feeders, coordinate the routes and price the alternatives. You can also see our full list of engineering services or contact us through the FutureGen Consulting website.

FAQ

Is busway the same as bus duct?

In common usage the two terms describe the same thing: a prefabricated enclosure of copper or aluminum busbars with fittings and tap-off devices. Busway is the term more often used for low-voltage plug-in and feeder systems, and bus duct is also used for larger or medium-voltage assemblies. Product standards and ratings differ by voltage class, so confirm the applicable standard for the project.

Is busway cheaper than cable tray?

Not on material. In the published 100-foot, 800 A comparison, bus duct totalled about $69,500 against about $23,000 for cable in tray, with labour reversing the ranking. Busway tends to become competitive at higher currents, with many tap-offs or on tight schedules, so a project-specific estimate is the reliable test.

Which Canadian Electrical Code rules apply?

In the 26th edition of Part I, busways and splitters fall under Rules 12-2000 to 12-2020, cable trays under Rules 12-2200 to 12-2208, and rigid and flexible metal conduit under Rules 12-1000 to 12-1014. Ontario adopts the code with amendments, so the Ontario Electrical Safety Code and the Electrical Safety Authority’s requirements govern the permit.

Can busway be modified after installation?

Tap-offs can be added or swapped with relative ease, which is the main reason it suits changing loads. The sections themselves are less able to be field modified than cable and tray, so lengths, fittings and tap locations should be coordinated before fabrication.

When is conduit better than either?

Conduit and wire is better suited to low-current runs to a specific load and to underground applications, and its parts are widely available for later replacement. It becomes labour-intensive as ampacity rises, because large feeders need multiple parallel runs.

Sources