Construction Specification For Electrical Busbar Trunking (Bus Duct) System

Busbar Trunking System (BBT) in electrical construction, uses to transporting electrical power to a shorter distance but many utilization point, say, within the building or a compound of facilities. Though cables can also be used in these areas, their economic impact would be high if compared to the effective Busbar Trunking System. It will help us to tap power directly from where we want it to be and make utilize to the service point.

Busbar Trunking System

Busbar Trunking System, a prefabricated trunk consisting of Copper / Aluminium busbars and suitable insulating medium. The size of the trunking system will be bigger for air insulated system compared to Sandwich type insulated Trunking system. A sample MEP specification of Busbar Trunking System is given here for the reference.

Electrical Busbar Trunking System

Construction and installation of Busbar Trunking (BBT) system included:

  1. Comply with the General Conditions, Supplementary Conditions and the requirements of concerned divisions / sections of the Electrical Specification. In addition read and conform to all Electrical Sections of these specifications. 
  2. Provide all labour, materials, products, equipment and services to supply and install the bus duct (busbar trunking) as indicated on the drawings and specified in these specifications.

Reference Standards for Electrical Busbar Trunking System

  1. All electrical installations shall be carried out in accordance with the best International Standards and Codes of Practice specifically with the current issue of the IEE Regulations (BS 7671) and the requirements of the supply authority.
  2. The entire installation shall be carried out and tested in accordance with the relevant National and International Standards and requirements of local authority.
  3. The design, manufacture, testing and performance of the busbar trunking system shall be in accordance with the latest edition of BSEN60439 – 1 & 2 (IEC 439 – 1 & 2) standard, BS5486-2 and AS 3439.2.
  4. Types and size of Busbar Trunking required for this project shall be in satisfactory service under similar conditions for not less than 5 years.
  5. Provide verification certificates prior to manufacturer for MEP Consultants review.
  6. The Busbar Trunking manufacturer shall be certified to the highest Quality Management System Standard, namely ISO 9001 and ISO 14001 for Environmental Management Systems.
  7. All busbar trunking shall include a CE MARK on its labels in accordance with the low voltage directive number 73/23/EEC

Approvals for Electrical Busbar Trunking System

  1. Do not commence final fabrication or erection of equipment until receipt of: Reviewed or reviewed as noted shop drawings from MEP Consultant.
  2. The following tests shall be carried out by the manufacturer on each piece of busbar trunking before it leaves the factory: 3.5kV Dielectric Test for 4 seconds; 1000V Megger Test
  3. A Factory Certificate of Testing and Inspection shall be submitted to the Engineer for review.
  4. Before installation each piece of busbar trunking shall be Megger tested at 1000V.
  5. On completion of the installation each busbar run shall be Megger tested at 1000V
  6. A temperature heat rise test in accordance with the manufacturer's recommendation/ procedure shall be carried out on site.
  7. All test results shall be recorded and submitted to the Engineer for review.
  8. The contractor shall carry out infra-red / thermal graphic scanning of the busbar systems and all test results shall be recorded and submitted to the engineer for review.
  9. The scanning shall be carried out under load conditions prior to handover.
  10. In addition the contractor shall allow for the scans to be repeated at the 'end of defects liability period' and a conditional report issued to the engineer for review.  Scanning shall be carried out at switchpanel terminations, changes of direction and on 10% of trunking joints.

Coordination for Electrical Busbar Trunking System

  1. The contractor shall ensure detailed co-ordination of installation and compatibility of busbar trunking, transformers and switchgear as appropriate.
  2. Connections to switchgear shall be with flanged end units and connections to transformers shall be with flanged end units, transformer box and flexibles, shall be of specific design and manufactured by the busbar trunking manufacturer.
  3. The contractor shall check and confirm structural penetrations through slabs and walls with the structural engineer prior to concrete pours or wall construction.
  4. In conjunction with the main contractor the MEP contractor shall co-ordinate the provision of 100mm high concrete curb at each opening where busbars rise through floor slabs.
  5. The contractor shall ensure the rising busbars, cable tray, distribution boards, tap-off arrangement and other services are co-ordinated in the riser space prior to installation.
  6. Busbar layouts indicated in the drawings are based on dimensions of a generic nature.  The contractor shall include for ensuring the selected busbar system can be installed in all locations without increase to room size or encroachment to other areas.
  7. The contractor shall carry out all necessary site measurements to ensure the busbar system is compatible with site dimensions and conditions.
  8. Confirm installed weight of busbar trunking with structural engineer.

Electrical Busbar Trunking System Installation

Products - Electrical Busbar Trunking System

The contractor shall supply, install, test and commission the busbar trunking system including flanges, elbows, tap-off boxes, supports etc., of the type and size as indicated in the drawings and locations designated on the drawings.  All busbar and associated installation shall be in accordance with the following requirements. The busbar shall carry its rated current without exceeding the temperature rise of 55ºC over an ambient of 50ºC at 90% relative humidity in any plane without de-rating and without effecting the local power supply requirements.

Storage of Electrical Busbar Trunking System

Store bus duct at site continuously in warm dry locations.  Bus bars or bus duct will be rejected if they have been roughly handled, or marked at joints or connection points, or plating is damaged in any way.  Do not install bus duct until that portion of the building is enclosed and dry.

Construction of Busbar Trunking

  1. The busbars shall be totally enclosed in a non-ventilated, low impedance sandwich design. The busbar trunking shall be sandwiched throughout it’s entire length, busbar trunking flared at tap-points are not acceptable.
  2. The enclosure shall comprise a non-magnetic aluminium housing with minimum metal thickness of 5mm top and bottom and 3mm sides.  The aluminium housing shall be unpainted natural finish and fully fault rated and provide additional protection by ASTA certified integral earthing (PE protective conductor).
  3. Each piece of busbar trunking shall be labelled E, L1, L2, L3, N at both ends to identify conductor phasing.
  4. Minimum enclosure protection shall be IP54 as defined in BSEN 60529 and must be ASTA certified in both horizontal and vertical positions.
  5. Copies of ASTA certificates for enclosure PE short-circuit and IP ratings shall be submitted to the Engineer for approval.
  6. All horizontal runs of the busbar trunking shall be designed for IP65 operation and IP54 for the vertical runs within risers.
  7. Ratings of Electrical Busbar Trunking System - 800A

    1. The busbar trunking shall be designed and constructed for use on a 400/415V, three phase, four wire, 50Hz system.  The minimum rated insulation voltage shall be 1000V. Each rating of busbar trunking shall be ASTA type tested and certified for short circuit ratings for one second covering phase, neutral, earth conductor and the housing as an additional protective conductor.
    2. Copies of ASTA test certificates shall be provided to the engineer for each rating for review.
    3. The minimum certified short circuit ratings of the busbar trunking shall be: 800A Rating, 35kA/1Sec, 74kA Peak 21kA N&PE

Busbar Conductors

  1. The phase and neutral busbar conductors shall be of rectangular section made of hard drawn high conductivity copper of 99.9% purity to BSEN13601: 2002, Cu-ETP, CW004A. A Declaration of Conformity from the copper supplier must be submitted to the Engineer.
  2. The neutral conductor shall be full rated, internal earth conductor shall be half rated and be of the same material as the phase busbars.
  3. The entire conductors and joint lengths shall be tinned. All busbar conductors shall be totally enclosed in Class B130ºC insulating polyester film material.
  4. An option for rating the bus bar neutral conductor at 200% rating shall be available and the contractor shall submit an optional cost with his tender offer.

Busbar Trunking Support

  1. The busbar trunking shall be properly aligned, and securely fixed, not exceeding 1.5m (or as recommended by the manufacturer) centres with support adequate to take the weight of the busbar by means of galvanized fixing brackets; comprising hanger clamp, fixing channel and damping screw, supplied by the busbar trunking manufacturer. Additional supports shall be supplied where required and where recommended by the trunking manufacturer.
  2. In vertical runs, busbars shall be designed to allow each section of trunking to be removed on one floor only without the need to dismantle the trunking on other floors.

Busbar Conductor Joints

  1. Joining of the busbar lengths shall be by means of a quick make non-reversible joint pack comprising a double headed, torque indicating single joint bolt, including a high visibility disc for visual indication of unmade joints. For ease of jointing and to minimize installation time, joints shall have a single torque bolt only.;
  2. The Joints shall be of a safe asymmetrical design to ensure correct phasing when jointing two lengths.
  3. It shall be possible to torque the joint using a standard long handle wrench with a 19mm socket.
  4. The joints shall accommodate 15mm of thermal expansion of conductors and housing without requiring additional expansion joints, except at building expansions.

Fire Protection for Busbar Trunking

  1. A declaration of fire resistance for 240 minutes minimum to ISO 834, BS 476, DIN 4102 Part 2 shall be provided by the busbar trunking manufacturers.
  2. Fire rated materials shall be fitted by the contractor to fill openings where busbar trunking passes through floors or walls with floor/wall flanges supplied by the busbar trunking manufacturer.

Tap-Off Positions and Tap-Off Units of Busbar Trunking System

  1. Busbar trunking shall have tap-off positions where shown on the drawings.  
  2. Each tap off position shall be provided with automatic safety shutters to shield the live busbars where the position is not occupied with a tap off unit. 
  3. Tap-off positions shall be non-flared and suitable for tap-off units to be plugged on to the busbars. 
  4. Shutters shall be activated by the insertion of the tap-off units and will only operate if the boxes are the correct way round.  
  5. The plug in contact shall self align with the busbars and plug-in openings shall provide personal protection and safety of IP 2X when in the open position and IP54 in the closed position in accordance with BS EN 60529.
  6. Within risers, plug-in tap-off positions shall be provided with a maximum distance of one plug-in opening for each 1000mm.
  7. Tap-off boxes shall be constructed of zinc plated sheet steel and shall be complete with hinged lids with an ASTA certified protective standard of IP54.
  8. The tap-off boxes shall have circuit protective devices as applicable and shown on the drawings with mechanical interlocks to prevent tap box removal unless the mechanism is in the off position.
  9. Where tap-off boxes are inserted into live busbar trunking, they shall be designed and constructed so that the current carrying metal parts are not exposed during the insertion and removal of the boxes.
  10. The tap-off box shall remain earthed during removal, until all live connections are disabled. The tap-off box shall ensure that the box can only be inserted to give correct polarity.
  11. All operational handles shall be pad lockable.
  12. Tap-off boxes up to 630A shall be of the plug-on type for ease of installation and removal.
  13. The tap-off units shall be MCCB current limiting type. The MCCBs shall compliment those used elsewhere (for the distribution panels) in order to allow co-ordination and future addition of shunt trip/motor operation devices.

Cast Resin Busbar

  1. Cast resin bus bar shall be utilised to achieve the fire rating requirement where noted on the drawings and called for in the specification (see concerned section).
  2. Generally the cast resin bus bars shall be as outlined above.
  3. Manufacturer: Recommended in the list of Manufacturer or equal and approved.

Execution of Electrical Busbar Trunking System Installation

  1. Installation manuals detailing handling, storage, installation, energisation, maintenance and joint assembly must be provided by the manufacturer. The contractor shall ensure that the busbar trunking is stored on site in accordance with the manufacturer’s installation manual, in a clean and dry environment.
  2. Provide low reactance bus duct system as specified and shown.
  3. Install system as specified and shown and as recommended by Bus Duct Manufacturer.
  4. Use a torque wrench to ensure uniform tension on bus duct joints.  After completion of installation, and before system is turned over to Owners, re-check each bolted joint with a torque wrench in an approved manner. Torque adjustment shall be as recommended by Bus Duct Manufacturer.
  5. Cover ventilated bus with a weatherproof heavy duty plastic envelope as soon as it has been installed.  Do not remove this cover until the building is clean and dry and bus ready to megger and energise.
  6. Megger each bus duct in an approved manner before it is energised.
  7. Bus duct layout throughout has been based on dimensions of a generic bus duct. The Contractor shall include for ensuring that the bus duct selected can be installed in locations indicated without any increase in contract price and without any increase to room size or encroachment of other areas.
  8. Ensure that adequate spacial provision and/or allowance is made for pouring resin compound when making joints on cast resin busbar.
  9. Ensure the rising busbars, cable tray, distribution board, tap off arrangement and other services are coordinated in the riser spaces prior to installation.
  10. Provide protective sleeves around bus ducts as they pass through walls and floors prior to making good.

Last Modified: 24-Jan-2019