Bus Duct vs Cable for Factory Distribution: When Each Wins

Choose per route, not per factory. Cable in tray usually wins for motor feeders, short runs and loads that will not move. Bus duct usually wins for high-current trunk routes with many tap-offs, such as the link from transformer to LT panel, a spine along the shop floor or a rising main, where space, fire load and future change count. The National Building Code leans towards bus trunking once cables start to bunch.

What are you actually comparing?

A factory has several kinds of route, and the answer changes between them. Before comparing prices, write down for each route the current it carries, its length, how many branch points it needs, how likely the machine layout is to change, the environment it passes through (dust, heat, wash-down, outdoors) and whether it crosses a fire compartment. A route that carries a few hundred amps to one motor is a different problem from a spine that feeds twenty machines. Cable sizing itself is covered in our note on voltage drop failures, and you can test a cable in the cable size calculator.

How do bus duct and cable compare?

No row decides the question alone. The cost line shows why a price comparison needs the whole installed route and not the cost of the metre: bus duct costs more as material and may save on terminations, tray, derating and labour.

What do the code and regulations say?

The National Building Code of India 2016, Part 8 Section 2, calls busbar trunking ideal for high load density and says it can run in riser shafts or horizontally in passages. It gives the grounds for choosing it: reduced fire load compared with cables, reduced maintenance over the life, longer service life and enhanced reliability because of rigid bolted joints and terminations. It also notes that even fire-resistant cable insulation loses that property when a large collection of cables is bunched, that specific limits on the number of cables and on bunching are not available, and that in such cases switching to a bus trunking system is the proper alternative.

The same clause, 5.3.8, says busbar or rising-main systems are preferred where heavy loads or multiple feeders are required. It asks for seismic supports where a straight run exceeds 24 m, for fire barriers of the same rating as the compartment where a bus duct crosses one, and for coordination of the bus duct with the connecting switchgear for protection. For cables, the code lists voltage drop (kept below 6 percent), the thermal limit with derating factors for the installation conditions, and the ability to withstand the fault current as the factors that decide size.

The CEA (Measures relating to Safety and Electric Supply) Regulations, 2023, regulation 38(3), applies to multi-storeyed buildings over fifteen metres and to other premises including industrial installations. It requires ducts for power cables to carry no other services and to have a fire barrier at each floor crossing, and says distribution of electricity to the floors shall be done using a bus bar trunking system. Read that in the light of your building: it speaks of floors, so it bites on a multi-level plant block more than on a single-storey shed. Ask the Electrical Inspectorate how your state applies it before you design a multi-level factory with cable risers.

Where does each tend to win inside a factory?

These are engineering judgements to test on your drawings, not rules.

• Transformer to main LT panel, and main panel to PCC: bus duct is common at high currents because the alternative is a large bunch of parallel cables; for short, low-current links cable is simpler.
• Shop-floor spine along machine bays: bus duct with plug-in tap-offs suits lines where machines are added or moved. Where the layout is fixed, cable in tray is cheaper to install.
• Motor feeders and final circuits: cable. Loads are individual and the run is short.
• Rising mains in multi-level plants: bus duct, supported by regulation 38 and NBC 5.3.8; confirm local interpretation.
• Dusty, wet or corrosive zones: armoured cable, unless the bus duct has a rating for the environment.
• Expansion routes: if you are likely to double capacity, ask which choice leaves headroom. Spare tap-off slots or a spare tray tier cost little at the start.

For the vertical riser case in particular see our note on busbar trunking against cable rising mains; the containment side is in raceway selection mistakes.

How do you budget the decision?

1. List the routes with current, length and branch points.
2. For each route, price both options as installed: material, supports, tray, terminations, derating margin, fire barriers, installation labour, and the shutdown needed to install or change it.
3. Ask suppliers for lead times in writing. A bus duct made to your survey takes manufacturing time that cable does not.
4. Choose the option with the lowest installed cost that meets the current, fault level, fire and environment limits and leaves headroom. Do not choose by material price alone.

This note quotes no prices. The drivers above are what a quotation should break out; a BOQ that lumps them together hides the comparison. Our cabling, cable tray and bus duct service page lists what a complete package includes.

How Secured Engineers helps

Secured Engineers designs the electrical distribution in-house, covering cable, tray and bus duct, and files the CEIG and DISCOM applications in-house. MEPF and solar can be delivered under one contract. The company works from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients.

If you already have a single-line diagram and a route list, send them for a budget review: we will mark which routes suit cable and which bus duct, and what the BOQ should break out. Use our cabling and bus duct page to see the scope, then message us on WhatsApp, call +91 70099 85817, or ask for a free proposal.