SERVICE CONNECTION, INSPECTION AND TESTING OF INSTALLATION
- 1. UNIT 4 SERVICE CONNECTION, INSPECTION AND TESTING OF INSTALLATION: Concept of service connection, Types of service connection and their features, Method of installation of service connection, Estimates of underground and overhead service connections, Inspection of internal wiring installations, Inspection of new installations, Testing of installations, Testing of wiring installations, Reason for excess recording of energy consumption by energy meter.
- 2. Concept of service connection • Service connection is the overhead or under ground cable connecting the supplier’s distributor line (in the ploe) to the consumer’s wiring (in the meter board). • It means of providing electric power supply from the eisting pole up to the meter board.
- 3. Types of service connection and their features There are two types of service mains 1) Overhead service connection 2) Under ground service connection. Overhead service connection are easy to errect, cheap and fault location with correction is ve easy. In case of additional power requirement only cable can be replaced which causes economy Underground service connection are having long life with safety. They have good appearance and is not affected by atmosphere & lightening surges.
- 5. THE FIGURE SHOWS THE OVERHEAD SERVICE CONNECTION FOR TAPPING A SINGLE-PHASE POWER SUPPLY. TOP MOST WIRE (1) WHICH TAKES MECHANICAL LOAD IS CALLED MESSENGER WIRE. THIS MESSENGER WIRE ED TO THE SUPPORTING PIPE (4) IN ONE SIDE AND TO THE POLE(6) ON THE OTHER SIDE. THE MESSENGER WIRE ROKEN AT BOTH ENDS BY MEANS OF I.1KV BREAK INSULATOR(8).TO THIS MESSENGER WIRE REEL INSULATORS ARE SUSPENDED THROUGH WHICH DOUBLE SHEATHED PVC CABLES (3) ARE DRAWN. FINALLY THE CABLES ARE EN TO THE METER BOARD (7) THROUGH SERVICE PIPE(5).THE SERVICE PIPE IS FIXED TO THE SUPPORT PIPE BY ANS OF CLAMPS .IF THE HORIZONTAL DISTANCE BETWEEN POLE AND SUPPORT PIPE IS MORE THAN 15 M ,THEN ORDER TO MAINTAIN SUPPORT PIPE VERTICALLY A STAY IS REQUIRED TO THE PIPE(USUALLY CALLED HALF POLE) CH IS TO BE BROKEN AT THE MIDDLE BY MEANS OF 1.1 BREAK KV BREAK INSULATOR IS TO BE PROVIDED. RTHING IS TO BE PROVIDED TO THE METER WITH 8 SWG G.I. WIRE. Method of Installation of overhead Service Connection
- 6. 1) MESSENGER WIRE: 10 SWG G.I WIRE. 2) SUPPORT PIPE : 40 MM DIAMETER 2.95 MM THICK G.I PIPE 1.8 M LONG FOR SINGLE PHASE OR 50 MM DIAMETER AND 2.95 MM THICK G.I PIPE 1.8M LONG FOR 3 PHASE INSTALLATION. 3) SERVICE PIPE :P.V.C PIPE 2MM THICK OF APPROPRIATE DIAMETER DEPENDING ON THE SIZE AND THE NUMBER OF CABLES TO BE TAKEN BY THE PIPE. USUALLY 2M IN LENGTH WITH 3 NUMBERS OF BENDS OF THE SAME DIAMETER. 4J BREAK INSULATOR : 1.1 K.V PORCELAIN BREAK INSULATOR. 5) SERVICE CABLES :DOUBLE SHEATHED PVC ALUMINUM CABLES OF APPROPRIATE SQUARE MM CROSS SECTION DEPENDING ON THE LOAD AND 250V GRADE IN CASE OF SINGLE PHASE AND 500V GRADE IN CASE OF 3 PHASE SUPPLY.THE STANDARD CROSS SECTION OF ALUMINUM IN SQUARE MM ARE 2.5,4,6,10,16,25,35,50,70,95, 120,150,185 AND 240 IN THE CABLES. . SECIFICATIONS OF MATERIAL USED IN OVERHEAD SERVICE CONNECTION
- 7. 6} METER BOARD :For single phase power connection teak wood back covered meter board 305 x 305 x 65mm made out of 15mm thick plank for front and 12mm plank for the back with 40 x 20 mm batten around (using fixing screws in front). For three phase power connection the back covered (box type) board size is 500 x 500 x 65 mm teak wood with 2 coats of high grade varnish with front plank of 15mm and back plank of 12mm thick. 7) EARTHING: 40mm diameter G.I pipe 2.95 mm thick, 2.5M long 12.5 mm holes drilled at an interval of 300mm. The whole pit of 340mm diameter is to be filled with coal and salt. 8} EARTH WIRE : It is 8 SWG. G.I wire, for connecting meter body to earth pipe. 9) FUSE UNIT : Porcelain fuse unit of required current rating and voltage grade
- 8. METHOD OF INSTALLATION OF U.G. SERVICE CONNECTION • Generally the under-ground cable system is preferred to that of over-head service system srticularly in cosmopolitan cities like Bangalore, Mysore, Mangalore, Hubli etc., • The figure 16. shows the usual U.G. service connection of sufficient current capacity and of required cords. The • U.G.cable (1) from the Meter Board (6) is taken to ground through G.I pipe using bends. In the ground sually trench laying is done in case of no obstruction. • However in case of road crossing etc, in the round also the cable is taken through G.I. pipe (2) using bends from where it is connected pot head (4) of suitable current range. • After this pot head, the supply is linked to thi double sheathed cables (5) which are flexible. • For a single phase twin core U.G. c; phase either 4 core or 3 and half core U.G. cable is used. Always we are select in U.G. cable . • The fixation of these steel armouring in a concentric way without affe, called BONDING
- 9. Different Methods of Laying UG Cable Are 1) Trench laying 2) Pipe laying 3) Trough wiring. 1) TRENCH LAYING(of Direct-laying System): Inthis method of laying UG cabl deep, 450 mm wide is dug along the route. Inside this a brick duct is formed ir is drawn at the center of this duct around which river sand is filled. Finally the also closed with brick. The cable indicator should be provided on top at an inte1 the route. DUCT OR PIPE LAYING(of Draw in System) : In this method pipe made up concrete or stone-ware are first laid inthe ground. Through these ducts the cat type of laying is usually used in road crossings. Cast iron ducts are used ir along the bridge & railway crossings etc. TROUGH WIRING (of solid System): In this method of laying pits or chanr along the route in which china clay or wood are laid.The cable is drawn in the tr bitumen compound is filled in the free space of the trough and finally covered
- 10. SPECIFICATION OF MATERIALS USED IN U.G. CABLE 1. Under ground cable(l.S 692/1957): Size of cable In square mm.such as 4, 6, 10, 16, 25, 35, 50, 70, 95, 12 Conductor material usually aluminium only(since over head lines are of ACS No of cores 2 for single phase, 3 or 3 112 or 4 for 3 phase. Insulation PVC sheathed with additional sheathing of either paper i lead alloy. Voltage grade 1.1 KV class for low and medium voltage. Armouring Steel wire armoured or tape armoured. 2. POT HEAD: Voltage grade 1.1KV or 11KV. Material Cast iron. Suitable for particular no. of core and size of cable: For ex. 2 core 10 sq mm cc: 3. STONE WARE PIPE (l.S. 1554 OF 1964): Size : 101.6mm dia. Length : 61 M. 4. G.I pipe (1.S 1239 of 1964 ): Dia - 40 mm for 6, 10 and 16 sq.mm cables or 50 mm dia for higher sizes
- 11. 5. PVC Cables Size: In sq.mm such as 2,4,6,10,16,25 etc., Conductor : Aluminium. Insulation : PVC Voltage grade : 1.1 KV METER BOARD: 300 x 300 x 65 mm box type teak wood varnished board for single phase or 500 x 500 x 65 mm box type teak wood varnished for 3-phase. EARTHING: 40 mm G.I pipe 3 mm thick, 2.5M long, 12.5 mm wholes drilled at an interval of 300 mm. The whole pit of 340 mm dia. is to be filled with coal and salt.
- 12. ESTIMATE FOR SERVICE MAINS Estimate for UG Service Mains lllusrative Example Q. Prepare a UG service connection to feed power supply to an A.E.H. lnstalltaion having a lighting load of 1020W and a power load of 3kW for a distance of 1OM. a) Materials for UG service connection Length of UG cable = Horizontal distance + looseness + meter side up to ground level + pole side = 1O + 2 + 3.5 + 4.5 = 20M Total load current = 4020/230 = 17.5A. therefore 16sqmm Alluminium U.G. cable is to be used (Taetking a factor of safety three ) 50A iron pot head of single phase (Two terminal), 250Vg 1Osqmm Alluminium double sheathed PVC cable = 12m for connecting U.G. cable to pole. No.of 11.5 x 23 x 7.5cm bricks 1O x 100/23 = 43.47 or say 45 Length of 40mm G.I. pipe = 2.5 x 2M (for both sides of poles) + 2.5M for earthing = 7.5M No. of 60A Fuse unit-3No. No.of 40mm GI bends 3 and 8 SWG G.I. wire 1Kg 300 X 300 X 65 TW meter board. Estimate of cost for service connection with UG cable Clamps & other miscellaneous materials such as coal,salt, bolts, nuts etc.,
- 13. SI. No. Particulars Unit Quantity Rate Rs.Ps. Cost Rs.Ps. 1. 200 x 100 x 75 mm bricks No. 45 3.00 135.00 2. 16sqmmAlluminium twin core steel armoured UG cable 1.1KV class M 20 80.00 1600.00 3 40mm GI pipe 3mm thick 5M for laying cable + 2.5M for earthing M 7.5M 140.00 1050.00 4 40mm GI bends 3mm thick No. 3 95.00 285:00 5 1Osq.mmAllumi nium double sheathed PVC cable 250Vg 100M(coil) 12M 1260.00 151.20 Estimate of cost for service connection with UG cable
- 14. 6. 6. 60A porcelain fuse unit 250Vg No. 1 145.00 145.00 7. Iron pot headwith 2 terminals 250Vg for 16 sqmm UGcable No. 240.00 240.00 8. Bitumenous compound KG 20.00 20.00 9. 8SWG GI wire for earthing KG 65.00 65.00 10. 300X300X65mm back coverd meter board No. 200.00 300.00 11. Clamp for holding pot head with pole No. 35.00 35.00 12. Clamp for holding GI pipe with pole No. 2 25.00 50.00 13. Miscellaneous materialas such as screws coal, salt, bolts, nuts, etc., Lumpsum 138.00 14. Labour charges a) Laying 150.00 300.00 b) Earthing work 50.00 Total 4514.20 Adding 5% for contingencies and unforeseen item 225.80 Total estimate of cost is Rupees four thousand seven hundred and forty only) Grand total Rs. 4740.00
- 15. Illustrative Examples for Overhead Service Main Q: Prepare an estimate for overhead service connection to feed power supply to a factory of 15H.P. load for a distance of 1OM. 1) Material calculation (for service connection):- 50mm G.I. Pipe 1.8M Approximate current = 1.6 X 15 = 24A Giving a factor of safety of 2, the current rating ( to be observed in the wire table) is 48A. The size of the aluminum cable is 16 sq. mm Length of each lead = 10 + 3 + 3 + 4 = 20M. Therefore the total length of cable required = 20 X 4 = 8OM No. of Break Insulator = 2 No. of reels = 4 (10 + 2) = 48 30mm PVC Pipe 2M & bends 3 Nos. 500X500X65 T.W. M Board -1 No. 40mm G.I. Pipe 2.5m for earthing & 1Kg of 8 SWG G.I. wire. 30A fuse unit-3Nos. & Misc. materials
- 16. SI. No. Particulars Unit Quantity Rate Rs.Ps. Cost Rs.Ps. 1 50mm G.I. pipe 3mm thick 1.8m for supporting M 1.8 250.00 450.00 2 1O SWG G.I. for massanging Kg. 1 68.00 68.00 3 16sq. mm aluminium double sheathed PVC cable 1.1 KV 100M (coil) 80M 1750.00 1400.00 4 Porcelain reel insulators 15mm dia. Gross 48Nos. 72.00 24.00 5 1.1 KV porcelain Break insulator Nos. 2 5.00 10.00 6 8SWG G.I. wire for earthing Kg. 65.00 65.00 7 30mm PVC pipe 2mm thick for servicing. 3M 2M 42.00 28.00 (length) 8 PVC Bends suitable for 30mm pipe No. 3 8.00 24.00 9 500 X 500 X 65mm T.W. back covered Meter board. No. 1 480.00 480.00 10 40mm G.I. Pipe 3mm thick M 2.5 190.00 475.00
- 17. 11 30A porcelain fuse unit 500Vg No. 3 60.00 180.00 12 12.5mm dia, 300mm eye bolt nuts of M.S. No. 2 25.00 50.00 13 Miscellaneous materials such as binding wire, pole clamp, supporting clamp, bolt nuts, coal, salt, cement etc. Lumpsum 146.00 14 Labour charges a) for servicing Rs. 150/- b) earth worlk Rs. 75/- 225.00 Tot al 3625.00 Adding contingencies and unforeseen things @ 5% 181.25 Grand Total 3806.25 Or say Rs. 3806.00 Estimate of cost for service main is rupees Three thousand eight hundred six only.