Sandwich Busway System


A Sandwich Busway System is a means to transfer electrical power from one equipment to another equipment in a low-voltage electrical network. The other ways to transfer electrical power in an electrical network are bare or insulated solid conductors and cables. Here our topic of discussion is Sandwich Busways, its construction, and its advantages over other means of power transfer.

Traditionally electrical industry used conventional air insulated busway systems where bare or sleeved conductors were placed inside a metallic enclosure. The medium of insulation between phases, phase to neutral and phase to earth is air and the reason for its name. Refer below picture for more clarity.

Air Insulated Busways
Air Insulated Busways

With the innovation in insulation technology, air is replaced with better insulating materials like miller, epoxy, and mica. Bare conductors wrapped in insulation layers and all the phases along with neutral put together without any air gap. Because of the better insulation properties of materials, the air gap between conductors is not needed. All the phase conductors along with neutral without an air gap look like a sandwich arrangement hence the name is Sandwich Busways. Refer to the below picture for more clarity.

Sandwich busways
Sandwich Busways

Why Sandwich Busway System?

Yes, now the question is why sandwich busway system and not cables? So here we will look for the answer. When an engineer designs a system, he always looks for an optimum solution. An optimum solution is one that technically fulfils the requirement of performance and safety at the minimum possible cost. For moderate ratings say, up to 800 A, cables are preferred, while for higher ratings of 1000A and above, the practice is to opt for solid conductors i.e., low-voltage bus systems. The reasons for the selection of bus systems are:

  • cost
  • appearance
  • safety
  • reliability
  • performance
  • ease of handling and
  • ease of maintenance

For larger ratings, more cables in parallel may become unwieldy and difficult to maintain. Locating faults is another big challenge. See the pictures of installations using cable and sandwich busways, the difference is palpable.

Next question, air-insulated or sandwich busway system?

Sandwich Busway system has lot many advantages over Air Insulated busways. With better aesthetics, much less space requirement, and better safety and reliability, Sandwich has the preference over Air Insulated Busways.

Using Sandwich busway is techno-commercially better than cables. A busway can have aluminium or copper as conductors. The use of copper will be more appropriate in corrosive areas such as humid, saline or chemically aggressive locations. In humid and corrosive conditions, aluminium erodes faster than copper.

Product Features

Sandwich busway system is much more compact compared to conventional busway systems and provides superior voltage drop characteristics, even at low power factors because of the low impedance of conductors compared to power cables. It is available up to a rating of 6300A, 100kA STC for 1 Sec and an operating voltage of up to 1000V. It is available in 3 phase 3 wire and 3 phase 5 wire bus bar configurations. The reference standard for the sandwich busways is IEC61439 Part 1 and 6.

Sandwich busways are being offered in steel and extruded aluminium enclosures by various manufacturers. A combination of steel and aluminium enclosure offers better electro-mechanical properties. In combination design Steel housing sides and aluminum tops and bottoms have been carefully designed to reduce component weight and minimize the hysteresis and eddy current losses that are common in steel housings.

Phase conductors are wrapped in Mylar insulation and placed side by side which makes sandwich busways very compact. Heat transfer by conduction makes it an efficient heat transfer system.

Advantage of Sandwich Busways System over Cable

  • Twice as quick to install
  • Integrated Electrical and Mechanical functions.
  • The jointing of two sections is quick and simple.
  • Disconnection from the source takes very little time around a quarter of an hour.
  • Approximately 40% lighter
  • More rigid
  • More compact in size requires less space.
  • Clean installation
  • Quick and easy maintenance
  • Easy to locate the faults.
  • Modular design help to quickly replace faulty section and up the system quickly.


  • Transformer/DG to switchboard connection
  • Switchboard to switchboard connection
  • Suitable for all kinds of installations like buildings, industries and offices
  • Horizontal distribution from the substation to the loads in the workshop
  • Vertical distribution from the substation to the loads of each high-rise floor in a building
  • Lighting application in supermarkets, exhibition centres, metro etc.

Sandwich Bus Trunking

Is it the same as Sandwich Busway? So the answer is yes, the only difference is the way they are getting connected. When it is connected between two equipments then it is called a Sandwich Busway but if one end is connected to a power source and the other end is open with output connections taken from plug-in points in between then it is termed Bus Trunking.

This kind of application is used in multi-story buildings where it runs vertically across the floors. Bus Trunking has a plug-in at each floor to take out power connections at each floor. Similarly in the process industry or any other industry where Bus Trunking parallelly runs horizontally along with machines and power output is taken from plug-in points to feed the machines.


From the discussion, we can conclude that the Sandwich Busway System is a better alternative compared to cable and Air Insulated systems. This is on account of safety, reliability, performance, faster installation, ease of working and maintainability.

Frequently asked questions

Q- Is Sandwich Busway available in both Aluminum and Copper?

A- Yes

Q- Is a Sandwich Busway compact compared to an Air Insulated System?

A- Yes

Q- Is Sandwich Busway also available in resin cast enclosure?

A- Yes

Q- Who are the major suppliers of Sandwich Busways in India?

A- Major suppliers of Sandwich Busway in India are:

  • Controls and Switchgear
  • Larsen and Toubro
  • Godrej
  • Schneider Electric etc.

Q- What is the available ingress protection in the sandwich busway?

A- IP54/IP55 for Indoor applications and IP66/67 for outdoor applications.

Q- What are the class of insulations are available?

A- Class B and Class F

External references

Some reference links are given below. More can be found on the internet.–fundamentals-of-low-and-medium-voltage-busway.html

6 thoughts on “Sandwich Busway System”

  1. Sir ! Very well explained the sbw and abw, respectively. And thanks for sharing the knowledgeable article. As per my experience and pint of views the IP 66 and 67 must have a canopy for outdoor applications.


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