Overhead Electric Lines and Street Lights

Overhead Electric Lines and Street Lights Points : overhead electric lines and street lights, poles, cross arms, insulators, stay set, struts, conductors, lightning arrestors, insulators, stay set, struts, conductors, lightning arrestors, painting of poles, completion report, type of earth electrodes, pipe earth electrode, watering arrangement, artificial treatment of soil, earthing lead, protection of earthing lead, completion report Poles Overhead lines shall be supported on steel tubular poles or steel rail poles. The steel tubular poles shall be of seamless / swaged and welded type and shall be in three stepped sections. Normally one sixth of the length of the pole shall be embedded in the ground. This length of the poles shall be coated with black bituminous paint, both internally and externally. The remaining portion of the pole shall be painted with one coat on its external surface. The pole shall be complete with .a cap and base plate. Steel tubular / steel rail poles shall be fixed over 1.5 cm thick bed of 1:3:6 (1 cement: 3 coarse sand : 6 graded stone aggregate of 40 mm normal size) foundation with not less than 20 cm thick layer of cement concrete all round the foundation being continued up to 30 cm above ground level and tapered suitably into a collar. The excavated portion shall be filled back with earth and consolidated properly using water, if necessary. The cement concrete foundation shall be cured properly using moist gunny bags before leading the pole. Cross Arms The cross arms shall be made of M.S. angle iron of size not less than 50 mm x 50 mm x 6 mm thick, The length of the cross arm shall be not less than 60 cm and shall have insulator pin holes so spaced as to accommodate one number Insulator on either side of (he pole with spacing of 45 cm between the conductors. The, cross arms shall be complete with pole clamp made of M.S. flat of size no( less than 50 mm x 6 mm with necessary bolts nuts and washers. When guard wire is also carried On the cross arm, the length of the cross arm shall be increased as that the guard wire runs not less than 30 cm beyond the outer most bare conductor. The cross arms shall be painted will red oxide primer before erection and finally painted with two coats of approved paint. Insulators The conductor shall be supported -an pins/shackle type of insulators. The insulator shall be fixed directly on clamp or on cross arm. The minimum size of shackle insulator shall be 90 mm dia x 75 mm high. The shackle insulators shall be complete with (G.i. bolts nuts and washers etc. The minimum size of pin insulator shall be 65 mm dia x 100 mm high. The pin insulator shall be complete with G.l. pin nuts and washers etc. Stay set A stay set shall consist of stay rod, anchor plate, bow lightener or turn buckle, thimbles, stay wire and strain insulator, clamp etc. The slay rod shall be provided with stay grip in case turn buckle is used instead of bow tightener. The entire stay assembly shall be galvanized. The stay wire shall be 7/10 SWG G.I. wire. The anchor plate shall be of M.S. galvanized and not less than 30 cm x 30 cm 6 mm thick and the size of stay rod shall not be less than 1.80 meters (6 ft.) long. A length of 46 cm (18”) of the rod shall project above the ground level. Struts A strut shall generally consist of a pole of the same section which it supports or slightly lighter. It shall be chamfered at the top so as to rest on the pole squarely and shall be secured by means of through bolt, nut, check nut and washers. It shall be buried in the ground to a depth of not less than 1.2 meter (4 ft) in the same manner as the pole. At the ground level, the strut shall be at a distance of not less than 1.8 meters (6 11) from the pole. Conductors Steel reinforced aluminum conductor (ACSR) shall be used for phase and neutral conductor., Important information about some common ACSR conductors is given in Appendix P. The minimum size of ACSR conductor shall be of code name “Squirrel”. No 8 SWG G.1. wire shall be used for earth conductor. The binding of the conductors with the insulators shall be done with 12 SWG soft aluminum conductors. The guard wire shall be of G.I, and shall have required breaking strength and current capacity to ensure rendering dead the line without risk of fusing guard wire. It shall be provided.

The conductor will be strained properly and care will be taken to see that there are no k:inks in the conductors. Joints in the conductors shall be staggered. All strands of conductors must be gripped securely when pulling the conductor. While stringing, conductors of sufficient length be kept at shackle termination for making jumpers. The jumpers shall be so made as to prevent occurrence of fault due to wind or birds.

Parallel (3roove(PG) clamps may be preferred to binding of conductors at jumper location or service tops. Jumpers will normally be of the same material as the line conductor and be of adequate current carrying capacity. The binding of conductor to insulator shall be sufficiently firm and tight to ensure that no intermittent contacts develop. Lightning arrestors Horn gap type of lightning arresters will be used wherever specified These shall be fixed with each phase at the terminals and other places where either side of the pole with spacing of 45 cm between the conductors. The, cross arms shall be complete with pole clamp made of M.S. flat of size no( less than 50 mm x 6 mm with necessary, bolts nuts and washers. When guard wire is also carried on the cross arm, the length of the cross arm shall be increased as that the guard wire runs not less than 30 cm beyond the outer most bare conductor. Th cross arms shall he painted will redoxide primer before erection and finally painted with two coats of approved paint. Insulators The conductor shall be supported on pins/shackle type of insulators. The insulator shall be fixed directly on clamp or on cross arm. The minimum size of shackle insulator shall be 90 mm dia x 75 mm high. The shackle insulators shall be complete with (.1.1. bolts: nuts and washers etc. The minimum size of pin insulator shall be 65 mm dia x 100mm high. The pin insulator shall be complete with G.I. pin, nuts and washers etc. Stay set A stay set shall consist of stay rod, anchor plate, bow lightener or turn buckle, thimbles, stay wire and strain insulator, clamp etc. The stay rod shall be provided with stay grip. in case turn buckle is used instead of bow tightened. The entire stay assembly shall be galvanized. The stay wire shall be 7/10 SWG GA. wire. The anchor plate shall be of M.S. galvanized and not less than 30 cm x 30 cm 6 mm thick and the size of stay rod shall not ‘be less than 1.80 meters (6, ft..) long. A length of 46 cm (18”) of the rod shall project above the ground level. Struts A strut shall generally consist of a pole of the same section which it supports or slightly lighter’. It shall be chamfered at the top so as to rest on the pole squarely and shall be secured by means of through bolt, nut, check nut and washers. It shall be buried in the ground to a depth of not less than 1.2 meter (4 ft) in the same manner as the pole. ‘At the ground level, the strut shall be at a distance of not less than 1.8 meters (6 If) from the pole. Conductors Steel reinforced aluminum conductor (ACSR) shall be used for phase and neutral conductor., Important information about some common ACSR conductors is given in Appendix P. The minimum size of ACSR conductor shall be of code name “Squirrel”. No 8 SWG G.I. wire shall be used for earth conductor. The binding of the conductors with the insulators shall be done with 12 SWG soft aluminum conductors. The guard wire shall be of G.I, and shall have required breaking strength and current capacity to ensure rendering dead the line without risk o1 fusing guard wire. It shall be provided.

The conductor will be strained properly and care will be taken to see that there are no kinks in the conductors. Joints’ in the conductors shall be staggered. All strands of conductors must be gripped securely when pulling the conductor. While stringing, conductors of sufficient length be kept at shackle termination for making jumpers.

The jumpers shall be so made as to prevent occurrence of fault due to wind or birds. Parallel Groove (P0) clamps may be preferred to binding of conductors at jumper location or service tops. Jumpers will normally be of the same material as the line conductor and be of adequate current carrying capacity. The binding of conductor to insulator shall be sufficiently firm and tight to ensure that no intermittent contacts develop. Lightning arrestors Horn gap type of lightning arresters will be used wherever specified. These shall be fixed with each phase at the terminals and other places where Painting of poles The painting of poles/struts including cross arms, clamps etc., will be carried out with aluminum paint. Painting shall not be done on wet surface. First of all the surface will be prepared, by removing all rust and scales by scrapping or by brushing with steel wire brushes. All dust and dirt shall be thoroughly wiped off. After this, the primer coat shall be applied with red oxide paint. When the primer coat has dried up and before any mixture, dirt dust etc settles down on the surface, aluminum paint shall be applied with brush and the paint shall be spread evenly and smoothly. The surface shall be given two or more coats as directed and shall finally present a uniform appearance. Mode of measurement of overhead conductors and earth wire. The weight of overhead conductor and earth wire shall be calculated by measuring the distance from center of one pole to the center of next pole and computing the weight of the conductor of that size and length by using standard tables. 3% extra shall be allowed for wastage, sag, jointing, building and jumpering etc. Completion report After completion, test results on the prescribed proforma (Appendix-F) and route layout and position of poles, duly marked on the building site plan shall be submitted by the contractor. The portion of the building etc. damaged during erection of installation shall be repaired properly to original finish and colour of the building etc. EARTHING General-Earthing shall conform to the following specifications. For other details not covered in these specifications, relevant Indian Standard shall be referred to I.S 3043, 1966 (Code of Practice for Earthing).

Earthing shall generally be carried out in accordance with the requirements of Indian Electricity Rules, 1956 as amended from time to time and the relevant Regulation of the Electricity Supply Authority concerned. The clauses of the Indian Electricity Rules, 195& particularly applicable are 32, 51, 61, 62, 67, 69, 88 (2) and 90.

All earth connections shall be visible for inspection. All medium voltage equipments shall be earthed by two separate and distinct connections with, earth through an earth electrode. In the case of high and extra high voltages the neutral points shall be earthed by not less than two separate and distinct connections with. earth each having its own electrode. Each electrode shall be provided at consumer premises and substations according to the requirement.

All material, fittings etc. used in earthing shall conform to the Indian Standard Specifications wherever these exist. In the case of materials for which ISS do not exist, the same will be approved by the competent authority. No earth electrode shall have a ohmic resistance greater than five ohms as measured by an approved earth testing apparatus. In rocky soils, the resistance may be up to Dight ohms. Use of plate electrode is recommended only where the current carrying capacity is prime consideration, for example, higher capacity main switches, panel boards and sub-. stations etc.. Normally, an earth electrode shall not be situated less than 1.5 m away from any building Care shall be taken that the excavations for earth electrode may not effect eh column footings or foundations of the building; in such cases electrodes may be fixed further may from the building.

The location of the earth electrode will be such where the soil, has reasonable chance of remaining moist, as far as possible. Entrances, pavements and roadways are to be definitely avoided for location of the earth electrode. Type of earth electrodes (a) pipe earth electrode; (b) plate earth electrode. G I pipe or G I plate earth electrode shall be used except when it is unavoidable to use copper plate earth electrode due to corrosive soil conditions, for D.C. system or for large capacity sub-stations. Where coil contains sulphur, copper electrode shall be adequately tinned. Pipe earth electrode G I pipe shall of 40 mm dia 4.5 metres in length..Galvanizing of the pipe shall conform to relevant Indian Standards. The pipe shall have a clean surface, not covered by paint, enamel or poorly conducting material. The pipe shall be of one piece. G I pipe electrode shall be cut tapered at the bottom and provided with holes of 12 mm diameter drilled and spaced 75 mm from each other up to 2 metres of length from bottom. The electrode shall be buried in the ground vertically with its top not less than 20 cm below ground level.

Plate earth electrode: For plate electrodes minimum dimension of the electrode shall be asunder:

(a) G I plate elctrode-6O0 mm x 600 m 6 mm thick
(b)Copper plate electrode-600 mm 600 mm 3mm thick.

The electrode shall be buried in ground with its face vertical and top less than 3 metres below ground level. Watering arrangement In the case of plate earth electrode, a watering pipe of 20 mm dia of G.I. pipe shall be provided and attached to the electrode as shown in the drawing. A funnel with mesh shall be provided on the top of this pipe for watering the earth. In the case of pipe electrode, a 40 mm x 20 mm reducer shall. We used for fixing the funnel. The watering funnel attachment (in both the above cases) shall be housed in masonry enclosure not less than 300. mm deep. A 300 mm x 300 mm cast iron cover frame with hinged cove having locking arrangement shall be suitably embedded in the masonry enclosure. Artificial treatment of soil The electrode. shall be surrounded by charcoal / coke and salt in alternate layers not less than 150 mm thick and indicate in the drawing. Earthing lead: (a) Main earthing lead-The main earthing lead shall be of G.I. wire or G.l. strip in case of G.l. plate earth electrode. For all electrical installations, except subs tations and generating stations, the earthing lead Shall not be less than one-half of cross-sectional area of the largest conductor to be protected. A conductor larger than 100 mm2 nominal cross-sectional area (2/0 SWG) in case of copper conductor and 150 rnm2 in case of GI conductor need to be used.

The minimum size of main earthing lead shall not be less than 8 SWG copper or G i. wire, or 12 mm x 3 mm copper gr G.I. strip.

(b) Earth continuity conductor-The nominal cross sectional area of an earth continuity conductor not contained within a cable or flexible cord shall be 14 SWG copper of 12 SWG G.l. or 4 mm2 aluminum wires.

In the case of plate earth electrode, the earthing lead shall be securely bolted to the plate with two 0.!. bolts, nuts, checknuts and washers. In the case of pipe earth electrode, it shall be connected by means of a through G.I. bolts, nuts and washers and cable sockets as indicated in the drawing. All material used for connecting the earth lead with electrode shall be .I. in case of Gi. pipe and G.I. plate earth electrodes and tinned brass in case of copper of plate electrode. The earthing lead shall be securely connected at the either end to the main board.

Loop earthing shall be provided for all mountings of main board and other metal clad switches and distribution fuse boards with not less than 14 SWG copper or 12 SWG G.l. or 4 mm2 aluminum wire. Protection of Earthing Lead The earthing lead from electrode onwards shall be suitably protected from mechanical injury by a 12 mm dia-G.L pipe in case of wire and by 40 mm diameter G.I. pipe in case of strip. Portion of the protection pipe within ground shall be buried at least 30 cm. deep arid shall be increased to 60 cm in case of road crossing and pavements. The portion within the building shall be recessed in walls and floors to adequate depth. Completion report After completion of the installation the test results and completion report of the installation work shall be submitted in the form given in Appendix-E.