Method for Installation of Earthing Strip

 

(A) Purpose:

• The method is to explain the procedure, which should be followed to install the Earthing Strip, Earthing Wire, and Earthing accessories as per the specification to achieve the standard requirements of the project.

(B) Equipment & Tools:

• The equipment that will be used for Installation of Earthing Strip / Wire works are

1. Ladder
2. Spirit Level
3. Drilling Machine
4. Grinding Machine
5. Cutting Machine
6. Power tools
7. Measure Tape
8. Screwdriver
9. Drill with bits
10. File
11. Galvanizing paint
12. Bitumius Paint

(C) Test for Earthing Strip / Earthing Accessories:

• Visual inspection:
• Type of Earthing Strip and Accessories Material
• Length , Width and thickness of Earthing Strip and Accessories
• Galvanization thickness
• Galvanization tests to be conduct.
• Proper painting / Galvanization and identification numbers of the Earthing Strip and Accessories
• The GS Flat to be supplied in 5.5 meters to 13 meters lengths.
• The weight of GS Flat
• MS flat shall conform to IS 2062 & its latest amendments for steel & Galvanization as per IS 4759 & its Latest amendments
• Physical Damages Inspection:
• Damage on Earthing Strip and Accessories
• Damage on galvanizing
• Testing of galvanizing:
• Uniformity of coating Thickness Test
• TRs not more than five year old shall be reviewed for acceptance.

Hot dip galvanization. (IS 2629)
Galvanizing	Minimum thickness:	Min. weight:
MS flats 5mm thick & over	75 microns (minimum)	610 gms. / sq. mtr.
MS flats under 5mm thickness	60 microns (minimum)	460 gms. / sq. mtr.
Pipes/ conduits with thickness over 5 mm	75 microns (minimum)	610 gms. / sq. mtr
Pipes/ conduits with thickness under 5mm	60 microns (minimum)	460 gms. / sq. mtr
GI Wire	20 Microns (Medium coated)	150 gms. / sq. mtr.

(D) Storage & Handling:

• The Earthing Flat shall be supplied in standard lengths.
• Materials should be stored according to a specification which is the maximum 1.5m height from the ground. Suitable support should be provided. The storage should be done in a designated area and proper covering should be provided.
• Earthing Strip and Accessories (pre-galvanized, hot dipped galvanized) shall be stored in a dry place, fully enclosed / ventilated store.
• When bringing down materials, they should be handled with care and lowered carefully to the ground. They should not be dropped.

(E) Preparation for Earthing Strip / Wire

• Check and ensure that the correct size and type of Earthing Strip & accessories are ready for installation.
• Ensure that the work area is ready and safe to start the installation of Earthing Strip.
• Ensure that Earthing Strip and accessories received from site store for the installation are free of rusty parts and damages.

(F) Earthing Strip Installation:

• Marking the Route:

• Mark the route of Earthing Strip with marking threads.
• The route of Earthing Strip to be coordinated with other services and shall be confirmed.
• Minimum space from the building structure and other services to be maintained (200 mm from the nearest point) to facilitate easy handling and maintenance.

• Satiating of Earthing Strip / Electrode:

• Hot-dip galvanized strip steel is aligned on simple straightening machines or on a parallel by hammer.

• Installation on Wall / Ground:

• GI strips used for earthing shall be minimum 6 mm thick and hot dip galvanized.
• If round GI conductors are used it shall have double the calculated area of cross-section.
• For installing earth leads on walls, special clamps are employed. They firmly accommodate the earth leads and are easily mounted. They are directly inserted in the wall or screwed to the wall. Fixing should be spaced not more than 1 m apart.
• Joints and junctions of earth leads and earthing concentration leads are to warrant a durable, safe and electrically well conductive connection.

• Where a Copper conductor is to be joined to GI, the joints should be tinned to prevent electrolytic action.
• If atmosphere is corrosive, GI conductors shall not be used for earthing.
• Earthing strips may be placed together with underground cables in cable Trench, but the heat from the cable must not be able to dry out the soil.
• Earth conductors in trenches having power or multi-core cables should be fixed to the walls near the top (for example, 100 mm from the top).
• Copper earth strip supported from or in contact with galvanized steel should be tinned to prevent electrolytic action.
• Sharp bends required in aluminum strip should be formed by the use of a bending machine.
• Earthing Strip which install below ground should be covered adequate insulating Sleeve for avoid corrosion.

• Earthing Electrode (Plate / Pipe):

• Minimum distance between earthing electrode (Plate /Pipe) and adjacent civil structure shall be 1.5 meter.
• Earthing grid should be run at a minimum depth of 50 cm below the ground.
• Since earthing electrodes will be damaged by corrosion, they are not to be placed in aggressive soil, in the vicinity of rubbish or in running waters.
• Transformer and generator neutral shall be double earthed. One independent earth electrode shall be provided for neutral earthing
• Earth electrodes (Plate /Pipe) shall be embedded as far apart as possible from each other. Mutual separation between them shall usually be not less twice the length of the electrode and are to be arranged in such a way as to prevent them from affecting each other.

• Earthing Bus-Bar:

• As far as possible, all earth connections shall be visible for inspection.
• All connections shall be carefully made, if they are poorly made or inadequate for the purpose for which they are intended, loss of life or serious personal injury may result.
• No cut-out, link or switch other than a linked switch arranged to operate simultaneously on the earthed or earthed neutral conductor and the live conductors,
• All earth electrodes shall be interconnected using the conductors of largest size in the earthing system.
• All non-current carrying metal parts of equipment’s shall be double earthed using conductors of adequate size.
• Earthing bus bars for screwing on wall / other constructions, distance of bores 35 mm.For connecting Flat strip with bore by flat head screws M10 (with anti-rotation feature), nuts and spring washer.

• Connection of Earthing Strip / Wire in Earthing Bus-Bar or to the body of equipment etc, such that it should be easily disconnected for testing purpose.
• By welding and drilling the zinc layer on the steel is damaged leading to stronger corrosion at the defective points.
• Welded joints are to be thoroughly cleaned from scale by means of a welder’s hammer prior to applying the anti-corrosive tape.

• Earthing Strip / Wire Jointing:

• Bolted, welded and pressed joints are permitted, In this case welded joints are being preferred Joints must be protected from corrosion.
• All Earthing Strip joined together with two bolt arrangement, cutting, bending, shaping jointing with nut bolts & lap welding joints at all junctions. All connection made by electric arc welding with low hydrogen content electrodes.
• Joints shall be allowed to cool down gradually to atmospheric temperature before putting any load on it. All oxide films that may have formed during welding must be removed from the welded joints
• Joints should be provided with coating alternative layers of red oxide and aluminium. Joints are to be covered with hot bitumen
• The interfaces of all ‘mechanical’ joins. Should be protected with a suitable electrical joint compound, particularly any bimetallic joints. All bimetallic joints should then be encapsulated in a grease impregnated tape, mastic compound or bitumastic paint, etc., to exclude moisture, In general, aluminum should only be used above ground and the connections to earth electrodes made above ground with bimetallic joints.  

• Joints using GI conductors should be welded as far as possible and kept separated from air by a thick coating of tar or similar non-hygroscopic materials. In case bolted joints cannot be avoided than there should be a minimum of 2 bolts for sizes up to 25 mm x 6 mm, 3 bolts for sizes up to 31 mm x 6 mm and zig-zag bolting for large sizes.
• When making a bolted type joint the surface of the Aluminum strip should be cleaned thoroughly by wire brushing and greased or an approved jointing compound applied immediately to both mating surfaces. Bolts should then be tightened and all excess grease or compound wiped off and discarded.
• All crossings of conductors in the main earth grid should be jointed. Compression type joints may be used for stranded conductors.
• Non-conductor strip should be drilled for a bolt having a diameter greater than one-third of the width of the strip. If this diameter will be exceeded, than a wider flag should be jointed to the strip.
• In case of bolted joints, at least a bolt M 10 has to be taken. For joining the earth lead to the auxiliary earthing electrode in case of applying the protective measure “voltage-operated earth-leakage protection” a bolt M 6 will suffice (Always hardened and tempered bolts with hexagonal head are to be used).
• Connections to natural earthing electrodes are preferably to be made outside the soil. At points where this is impossible and at joining faces being not metallic-bright, toothed lock-washers are to be used. At joining faces being metallic-bright, joints between earthing electrodes may be made by applying spring lock washer resp. plain lock washers. At the joints of earthing electrodes protection against corrosion is of utmost importance. It must be durable and fully effective.

 

OVERLAPPING OF EARTHING STRIP
SR.NO	SIZE OF EARTHING STRIP	MIN.OVERLAPING
1	20×3	20MM
2	20×6	20MM
3	25×3	25MM
4	25×6	25MM
5	32×6	25MM
6	40×5	50MM
7	40×6	50MM
8	50×6	50MM
9	50×10	50MM
10	75×6	50MM
11	75×10	50MM

NO’S AND SIZE OF NUT BOLT FOR JOINTING EARTHING STRIP
SR.NO	SIZE OF EARTHING STRIP	MIN.NUT BOLT REQUIRED	MIN.SIZE OF NUT BOLT
1	20×3	2 NO’S	8X25MM
2	20×6	2 NO’S	8X25MM
3	25×3	2 NO’S	8X25MM
4	25×6	2 NO’S	8X25MM
5	32×6	2 NO’S	8X25MM
6	40×5	4 NO’S	8X25MM
7	40×6	4 NO’S	8X25MM
8	50×6	4 NO’S	10X25MM
9	50×10	4 NO’S	10X25MM
10	75×6	4 NO’S	10X25MM
11	75×10	4 NO’S	10X25MM

• Jointing conductors:

• Aluminum to aluminum: When possible, 4 joints on strip conductor should be Bolted or arc welded using either the tungsten inert-gas arc ( TIC ) or metal inert gas arc ( MIG ) techniques. Oxy-acetylene gas welding or brazing may also be used.
• Rectangular Strip can be joined or terminated by drilling and bolting.
• When making a bolted type joint, the surface of the aluminum should be cleaned thoroughly by wire brushing and greased or an approved jointing compound applied immediately to both mating surfaces. Bolts should then be tightened and all excess grease or compound wiped off and discarded. To ensure adequate contact pressure and avoid overstressing, torque spanners should be used. The conductor manufacturer’s literature should be consulted for further details for the joints and procedures.

• Aluminum to copper:

• Joints between aluminum and copper should be of the bolted type and be installed in the vertical plane at a minimum distance of 150 mm above ground level.
• The rating surface of the aluminum should he cleaned thoroughly by wire brushing and greased or an approved jointing compound applied and the copper tinned. Grease or an approved jointing compound should be applied to the melting surface of the aluminum.
• After bolt tightening by torque spanner, excess grease or compound should be wiped off and discarded, and the joint protected from the increase of moisture by the application of suitable plastics compound or irradiated polyethylene sleeve with mastic lining. Alternatively, the joint may be protected by a bitumastic paint.
• Aluminum conductor connections to equipment should, where possible, be in the vertical plane. Surface preparation of the aluminum and the making of the joint should be as previously described. The finished joint should be protected by a bitumastic paint.
• Earthing strip shall not have any cut-outs or switches or links.
• All material, fitting etc. used for earthing and earthing pit should be of IS specified make and standards.
• Two separate and distinct connections shall be taken out from plate earthing.
• Interconnection of earth and main branch of earth should be made in such a way that reliable and good electrical contact is established.
• The path of earthing strip should be minimum as possible, be out of reach of any person. For earth resistance please refer to IS-3043:1966-10 page –32. h).
• Anti-corrosive measures: Earth strip should be protected against mechanical damages and corrosion. Fittings should be resistant to the corrosive agencies or be otherwise suitably protected. Joints and bonds may be protected with bitumen or embedded in plastic compound according to the local conditions.
• No conductor strip should be drilled for a bolt having a diameter greater than one-third of the width of the strip. If this diameter would be exceeded then a flat should be jointed to the strip
• Aluminum or copper conductors should not be drilled for fixing to structures. Clips should be used that prevent contact between conductor and structure and which are of suitable material so that there is no electrolytic action between clip and conductor.
• Fixings should be spaced not more than 1 m apart. Earth conductors in trenches containing power and/or multi-core cables should be fixed to the walls near the top (e.g. 100 mm from the top).
• Copper earth strip supported from or in contact with galvanized steel should be tinned to prevent electrolytic action. If sharp bends are required in aluminum strip they should be formed by the use of a bending machine to avoid stress concentration. Aluminum is prone to corrosion when in contact with Portland cement and mortar mixes. Contact of aluminum conductors with such materials should, therefore, be avoided by the use of stand-off fixings.

(G) Standards:

• IS:3043-1987 :Code of Practice for Earthing (first revision)
• Indian Electricity Rules :1956 (latest edition)
• National Electrical Code :1985 of Bureau of Indian Standards
• IEEE Guide for safety in a. c. substation grounding. No. ANSI/IEEE Standard 80-1986.