DUBAI WORLD CENTRAL INTERNATIONAL AIRPORT
PHASE I – Design of Buildings
Contract No. JXB1/BLD/431- PASSENGER TERMINAL BUILDING
GROUNDING AND BONDING
PART 1 - GENERAL
1.5DEFINITIONS OF TERMS
PART 2 - PRODUCTS AND SYSTEMS
2.1STANDARD COMMERCIAL PRODUCTS
2.2SOIL SURVEY AND CALCULATIONS
2.3FAULT CURRENT AND DURATION
2.4EARTH ELECTRODE SYSTEM DESIGN
2.7CONNECTOR PRODUCTS AND EARTHING ACCESSORIES
PART 3 - EXECUTION
3.1TRANSFORMER SUBSTATION EARTHING
3.2EARTHING OF MAIN DISTRIBUTION BOARDS, PANELBOARDS, LIGHTING INSTALLATIONS AND WIRING ACCESSORIES
3.3ELECTRICAL / MECHANICAL PLANT ROOMS AND FIXED MACHINERY
3.5SIGNAL AND COMMUNICATION SYSTEMS
3.6CLEAN EARTH GROUNDING
3.7EARTHING AND BONDING MULTICORE CABLES
3.8EARTHING OF FENCES
3.11FIELD QUALITY CONTROL
3.12GRADING AND PLANTING
PART 1 - GENERAL
1.1 RELATED DOCUMENTS
- Drawings and general provisions of the Contract, including Conditions of Contract and Division 1 Specification Sections, apply to this Section.
- The following Sections contain special requirements that relate to this Section:
- Division 2 Section "Underground Ducts and Utility Structures" for ground earth pits.
- Division 13 Section "Lightning Protection" for additional grounding and bonding materials.
- Division 16 Section "Basic Electrical Materials and Methods".
- Division 16 Section "LV Conductors and Cables".
- This Section includes complete installations to earth every source of energy and to provide protective earthing and equipotential bonding, based on the TN-S system arrangement, including:
- 11kV Switchgear and Ring Main Unit (RMU).
- Transformer neutral earthing.
- Generator sets neutral point
- LV Switchgears.
- Main earthing terminals or bars in electrical and mechanical rooms.
- Exposed conductive parts of electrical equipment (light fittings, switches and socket outlets, etc.).
- Extraneous conductive parts.
- Fences & gate earthing.
- Separate clean earth for the ELV systems for each ELV and control room (less than 1 ohm)
Earthing requirements specified in this Section may be supplemented by special requirements of systems described in other Sections.
- Product Data: Prior to ordering materials, submit data for approval including, but not limited to, manufacturer’s catalogs for each type of product indicated including the following:
- Ground rods.
- Connecting clamps.
- Earthing conductors, protective conductors, and bonding conductors.
- Connectors and other accessories.
- Exothermic welding kits and tools.
- Qualification Data: For firms and persons specified in "Quality Assurance" Article.
- Field Test Reports: Submit certified, numbered, written test reports to include the following:
- Test procedures used and test conditions.
- Test results that comply with requirements.
- Results of failed tests and corrective action taken to achieve test results that comply with requirements.
- Shop and Construction Drawings: Submit Drawings for approval including, but not limited to, the following:
- Overall earthing schematic indicating cross sectional area of all earthing, protective and bonding conductors.
- Overall earthing layout indicating earthing provisions at substations, generator rooms, switchgear, distribution panel boards etc., identifying fittings used, insulation, plates and marking, passage and routing of earthing conductors, conduit, sleeves, grooves, niches etc., giving sizes and dimensions of component parts, and exact location of earth pits, rods and details of installation and connections, and exact routing of buried earthing conductors with indication of cross-section, depth of laying and covering.
- Records: Submit the following:
- Scaled Drawings, As-built, showing actual layout and specification of all components of earthing system, in accordance with requirements of the Specification, Division 1.
- Nature of soil and any special earth arrangements etc.
- Date and particulars of soil conditioning method and agents if used.
- Samples: Submit samples of conductors, as requested.
- Final earthing design calculations for approval, clearly indicating expected maximum earth fault levels and suitable conductor sizes, before implementation.
1.4 QUALITY ASSURANCE
- Installer Qualifications: Engage an experienced installer. Submit qualifications for approval.
- Standards: Carry out work in accordance with the following:
- IEC 60364-1 and 60364-4-41: Electrical Installations in Buildings.
- BS 7671 Requirements for Electrical Installations (IEE Wiring Regulations 16th Edition).
- Comply with BS 6651 (Protection of Structures against Lightning) when interconnecting with lightning protection system.
- ANSI/IEEE/std 80: IEEE Guide for Safety in AC Substation Grounding.
- ANSI/IEEE/Std 81: IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potential of a Grounding System.
- BS 7430: Code of Practice for Earthing.
- DIN VDE 0141: Earthing Systems for Power Installations with Rated Voltages above 1 kV.
- BS EN 13601 Copper and copper alloys. Copper rod, bar and wire for general electrical purposes.
- BS 1433: Specification for copper for electrical purposes. Rod and bars.
- BS EN 1057: Copper and copper alloys. Seamless round tubes for water and gas in sanitary and heating applications.
- BS EN 12449: Copper and copper alloys. Seamless round tubes for general purposes.
- BS EN 12451: Copper and copper alloys. Seamless, round tubes for heat exchangers.
- BS 7668: Specification for weldable structural steels. Hot finished structural hollow sections in weather resistant steels.
- BS 6360: Specification for conductors in insulated cables and cords.
- BS EN 10029: Specification for tolerances on dimensions, shape and mass for hot rolled steel plates 3 mm thick or above.
- BS EN 10113-1: Hot-rolled products in weldable fine grain structural steels. Delivery conditions for thermomechanical rolled steels.
- BS EN 10113-2:1: Hot-rolled products in weldable fine grain structural steels. Delivery conditions for normalized/normalized rolled steels.
- BS EN 10113-3: Hot-rolled products in weldable fine grain structural steels. Delivery conditions for thermomechanical rolled sheets.
- BS EN 10155: structural steels with improved atmospheric corrosion resistance. Technical delivery conditions.
- BS EN 10210-1: Hot finished structural hollow sections of non-alloy and fine grain structural steels. Technical delivery requirements.
- BS EN 10137-1: Plates and wide flats made of high yield strength structural steels in the quenched and tempered or precipitation hardened conditions. General delivery conditions.
- BS EN 10137-2: Plates and wide flats made of high yield strength structural steels in the quenched and tempered or precipitation hardened conditions. Delivery conditions for quenched and tempered steels.
- BS EN 10137-3: Plates and wide flats made of high yield strength structural steels in the quenched and tempered or precipitation hardened condition. Delivery conditions for precipitation hardened steels.
- BS EN 10025: Hot rolled products of non-alloy structural steels. Technical delivery conditions.
- BS 7655-1-5: Specification for insulating and sheathing materials for cables. Elastomeric insulating compounds. Flame retardant composites.
- BS 7655-0: Specification for insulating and sheathing materials for cables. General introduction.
- BS 6004: Electric cables. PVC insulated, non-armoured cables for voltages up to and including 450/750 V, for electric power, lighting and internal wiring.
- ISO 630: Structural steels.
- IEC 60502-1: Extruded solid dielectric insulated power cables for rated voltages from 1 kV to 30 kV.
- ITU: Directives concerning the protection of telecommunications lines against harmful effects from electricity lines.
- Comply with BS 6651 when interconnecting with lightning protection system.
- DEWA regulations
- Products shall be sourced either directly from manufacturer or from the manufacturer’s authorized dealer/agent.
1.5 DEFINITIONS OF TERMS
- The following terms used on the Drawings and in the Specifications are equivalent and may be used interchangeably: "earth" and "ground"; "earthing" and "grounding".
- Earth: Conductive mass of the Earth whose electric potential at any point is conventionally taken as zero.
- Earth Electrode: Conductor or group of conductors in initial contact with, and providing electrical connection to, Earth.
- Exposed Conductive Part: Any part which can be readily touched and which is not a live part, but which may become live under fault conditions.
- Extraneous Conductive Part: Any conductive part not forming part of the electrical installation such as structural metalwork of a building, metallic gas pipes, AC ducts, water pipes, heating tubes etc. and non-electrical apparatus electrically connected to them i.e. radiators, cooking ranges, metal sinks etc. and non-insulating floors and walls.
- Protective Conductor: Conductor used for some measure of protection against electric shock and intended for connecting together any of the following parts:
- Exposed conductive parts.
- Extraneous conductive parts.
- Earth electrode(s).
- Main earthing terminal or bar(s).
- Earthed point of the source(s).
- Electrically Independent Earth Electrodes: Earth electrodes located at such distance from one another that maximum current likely to flow through one of them does not significantly affect the potential of the other(s).
- Main Earthing Terminal or Bar: The terminal or bar provided for the connection of protective conductors, including equipotential bonding and functional earthing conductors, if any, to the means of earthing.
- Equipotential Bonding: Electrical connection to put exposed and extraneous conductive parts at a substantially equal potential.
- Earthing Conductor: Protective conductor connecting main earthing terminal or bar of an installation to earth electrode or to other means of earthing.
PART 2 - PRODUCTS AND SYSTEMS
2.1 STANDARD COMMERCIAL PRODUCTS
- Refer to Division 1 Section 01600, paragraph 2.1
2.2 SOIL SURVEY AND CALCULATIONS
- The Contractor shall carry out an earth resistivity survey on each site and report in writing to the Engineer in accordance with the approved program. The report shall detail the methods and instruments used and the results of the surveys. Based on the results the Contractor shall include in the report his proposals for the resistivities to be used in the design of the earthing system.
- The value of resistivities to be used in the design of the earthing system shall be subject to the Engineer’s approval.
- The surveys shall show the variation of resistivity across the site and with the depth below the site. The Contractor shall consider if there is a need to model the resistivity in two layers and if there is any advantage in the use of long rods. The surveys shall also determine the depth and nature of any underlying rock, which may limit the depth for driving earth rods or if boring will be necessary for installing earth rods.
- The weather conditions prior to and at the time of the surveys shall be recorded in the report and an assessment made of the seasonal variations in resistivity based on meteorological data for the area. The program for the project should, as far as possible, time the resistivity surveys to take place during a dry season.
- The report should also state if there are any indications that the ground is corrosive to copper or if there is any risk of galvanic corrosion on other metal structures in the neighborhood.
- The report shall be approved by the Engineer before proceeding with the design of the earthing system.
- The calculations shall be submitted for approval prior to commencing the design of the earthing systems.
2.3 FAULT CURRENT AND DURATION
- The earthing system design calculation by the Contractor shall be based on earth fault withstand current shown in DEWA General Design Criteria Standard 18.104.22.168.0.01.
- The estimated maximum duration of the fault current shall not be less than 5.0 seconds for the 11kV system.
2.4 EARTH ELECTRODE SYSTEM DESIGN
Delete or retain the following paragraph, if not required for the project.
- Design Calculations:
- The design of the earth electrode systems shall be based on the approved earth resistivity data and the system’s fault currents and their duration.
- The design calculations shall be to the approval of the Engineer and shall be based on the methods given in the standards listed. The calculations shall include the following parameters:-
- Earth resistance of the whole system of its components.
- Earth potential rise.
- Step, touch and mesh potentials inside and outside the perimeter fence.
- Requirements for a high resistance surface layer.
- Conductor ratings.
- The earth potential rises shall not exceed the ITU limits appropriate to the classification of the system unless special precautions are taken to cater for transferred potentials.
- Step, touch and mesh potentials shall be within the limits calculated in accordance with the standards given in IEEE 80 and BS 7430 for the proposed surface layer. The formula for allowable body current shall be used for 50 Kg body weight.
- Earth Electrode:
- The earth electrodes shall comprise a system of bare conductors forming a mesh buried near the surface of the ground supplemented, as necessary, by one or more of the following electrodes:
- A system of interconnected steel rods driven into the ground.
- Structural steel metalwork in direct contact with the ground.
- Reinforcing steel in buried concrete.
- Mesh System:
- The mesh system shall be designed in accordance with paragraph A "Design calculations" above to limit touch, step and mesh potentials taking into account the combined length of the mesh conductors, other buried conductors and rods but excluding any buried conductors outside the perimeter fence. Due regard shall be given to non-linear distribution of the fault current giving rise to the highest potentials at mesh corners.
- The rating of the mesh conductors shall be compatible with the fault currents after allowing for parallel paths with a minimum conductor size of 300 mm2 copper.
- The current division factors = 0.8 of given fault current shall be taken for design calculations of ground mesh.
- If the placement of earthing mesh is designed for outside of the building, the depth of mesh shall be 2 m below the ground level or this shall be at least 1 m below the power cables of standard depth.
- Interconnected Rods:
- If the design calculations show that a mesh alone is unable to limit the potentials to the required values, then the mesh shall be supplemented by the use of interconnected earthing rods driven into the ground or installed in bored holes.
- Rods shall be installed inside the perimeter fence to enclose the maximum possible area compatible with the earthing of any metallic fence. (The spacing between rods shall not be less than their length, unless rating considerations determine otherwise). The rods shall be interconnected in groups of 4 to 10 rods by yellow-green colored PVC insulated stranded copper conductors to form a ring. Each group shall be connected to the mesh by duplicate insulated copper conductor via disconnecting test links.
- Individual rods may be connected directly to the mesh provided the conductor to the rod can be disconnected for testing the rod.
- Rods installed in bored holes may be used to reach lower resistivity ground strata at depths beyond the reach of driven rods or where rock is encountered and it is not possible to drive rods. After installing the rod the bored hole shall be back-filled with a low resistivity liquid mixture that shall not shrink after pouring to ensure good contact between the rod and the ground for the life of the installation.
- The resistance and rating of individual rods and the combined resistance of the groups of rods in the proposed design shall be calculated and the rating of the interconnecting conductors shall not be less than that of the main grid conductor.
- The calculation of potentials in the design of the complete installation shall be made without the group of rods with the lowest estimated resistance to simulate the condition with the group disconnected for testing.
- Reinforcing Steel:
- The reinforcing steel in the foundations of buildings containing the primary electrical equipment may be used as auxiliary electrodes subject to the approval of the Engineer. The Contractor shall show in the design calculations that the fault currents and d.c. stray currents will not damage the structure.
- Steel reinforcing mesh in the floors of the building may also be used for the control of step and touch potentials within the building subject to the approval of the Engineer.
- Conductors Outside Perimeter Fence:
- If the design calculations show that the step and touch potentials outside the perimeter fence, gate or wall exceed the limits then additional bare conductors shall be buried in the ground outside the fence in the form of rings encircling the whole site.
- The distance of the conductors from the fence and the depth shall be determined in the design to ensure that step and touch potentials are within the limits.
- The minimum conductor size shall be 70 mm2 and shall be connected to the fence or the mesh with 70 mm2 conductors at each corner of the site and at intervals of not more than 100 m. These conductors shall not be included in the calculations called for above.
2.5 GENERAL REQUIREMENTS
- Component parts of earthing system are to include the following:
- Earth electrode (rods, tapes etc.)
- Main earthing terminals or bars.
- Earthing conductors.
- Protective conductors.
- Equipotential bonding conductors.
- Electrically independent earth electrodes for special systems (clean earth).
- Accessories and termination fittings, bonding, welding kits and other materials.
- Earth electrode is to consist of one or more earth rods, interconnected by buried earthing tape or cable, which is to have a total combined resistance value, during any season of the year and before interconnection to other earthed systems or earthing means, not exceeding 1 ohm. Distance between 2 rods is not to be less than 6 meters.
- Main ring earthing resistance should not exceed 1 ohm.
- Ring type earth electrode is to consist of earthing conductors, in a closed loop, buried in exterior wall foundations underneath the water-proofing, or alternatively at 0.6 m around the perimeter of the building foundations, as shown on the Drawings. Connect all earthing conductors to this ring. Insulated connection flags into the building, of same material as earthing conductors, are to be located at positions of service entrance and main switchboard rooms, terminating in bolt-type earth points (studs) or test links for connection of main earth bar(s). Additional earth rods connecting with the earth ring are to be provided, as necessary, to bring down earth electrode resistance to an acceptable value.
- Functional earth electrode is to be provided separately from, but interconnected to, other earth electrode(s) through suitably rated (470 V) spark gap.