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Chapter-VIII- Indian Electricity Rules

Indian electricity rules, 1956

Chapter-VIII
1over-head lines, underground cables & generating stations

74. Material and strength

(1) All conductors of overhead lines other than those specified in sub-rule (1) of rule 86 shall have a breaking strength of not less than 350 kg.

(2) Where the voltage is low and the span is of less than 15 metres and is on the owner's or consumer's premises, a conductor having an actual breaking strength of not less than 150 kg. may be used.

75. Joints

Joints between conductors of overhead lines shall be mechanically and electrically secured under the conditions of operation. The ultimate strength of the joint shall not be less than 95 per cent of that of the conductor, and the electrical conductivity not less than that of the conductor:

2PROVIDED that no conductor of an overhead line shall have more than two joints in a span.

376. Maximum stresses, factors of safety

(1) The load and permissible stresses on the Structural members, conductors and ground wire of self supporting steel lattice towers for overhead transmission lines shall be in accordance with the specification laid down, from time to time , by the Bureau of Indian Standards.

(2) Overhead lines not covered in sub-rule (1) shall have the following minimum factors of safety:

Details
(i) for metal supports 1.5
(ii) for mechanically processed concrete supports 2.0
(iii) for hand moulded concrete supports 2.5
(iv) for wood supports 3.0

Explanation I: The minimum factors of safety shall be based on such load as may (sic) cause failure of the supports to perform its function (assuming that the foundation and other components of the structure are intact).

Explanation II: The load shall be equivalent to the yield point stress or the moulds of rupture, as the case may be, for supports subject to bending and vertical loads and the crippling load for support used as struts.

Explanation III: The strength of the supports of the overhead lines in the direction of the line shall not be less than one-fourth of the strength required in the direction transverse to the line.

Explanation IV: The minimum factor of safety for the stay wires, guard wires or bearer wires shall be 2.5 based on the ultimate tensile strength of the wire.

Explanation V: The minimum factor of safety for conductors shall be 2 based on their ultimate tensile strength. In addition, the conductor tension at 32°C, without external load shall not exceed the following percentages of the ultimate tensile strength of the Conductor:

Details
Initial unloaded tension 35 per cent
Final unloaded tension 25 per cent

PROVIDED that the conductors having a cross section of a generally triangular shape, such as conductors composed of 3 wires the final unloaded tension at 32°C, shall not exceed 30 per cent of the ultimate tensile strength of such conductor.

(3) For the purpose of calculating the factors of safety specified under sub-rule (2):

(a) The maximum wind pressure shall be as specified in the relevant Indian Standards;

(b ) For cylindrical bodies, the effective area shall be taken as full projected area exposed to wind pressure; and

(c) The maximum and minimum temperature shall be as specified in the relevant Indian Standard.

(4) Notwithstanding anything contained in sub-rules (2) and (3), in localities where overhead lines are liable to accumulations of ice or snow the appropriate Government may, by order in writing specify the loading conditions for the purpose of calculating the factor of safety.

77. Clearance above ground of the lowest conductor

(1) No conductor of an overhead line, including service lines, erected across a street shall at any part thereof be at a height less than-

Details
(a) for low and medium voltage lines - 5.8 metres
(b) for high voltage lines - 6.1 metres

(2) No conductor of an overhead line, including service, lines, erected along any street shall at any part thereof be at a height less than-

Details
(a) for low and medium voltage lines - 5.5 metres
(b) for high voltage lines - 5.8 metres

(3) No conductor of an overhead line including service lines, erected else- where than along or across any street shall be at a height less than-

Details
(a) for low, medium and high voltage lines up to and including 11,000 volts, if bare ; - 4.6 metres
(b) for low, medium and high voltage lines up to and including 11,000 volts, if insulated 4.0 metres - 4.0 metres
(c) for high voltage lines above 11,000 volts - 5.2 metres

(4) For extra-high voltage lines the clearance above ground shall not be less than 5.2 metres plus 0.3 metre for every 33,000 volts or part thereof by which the voltage of the line exceeds 33,000 volts:

PROVIDED that the minimum clearance along or across any street shall not be less than 6.1 metres.

78. Clearance between conductors and trolley wires

4(1) No conductor of an over-head line crossing a tramway or trolley-bus route using trolley wires shall have less than the following clearances above any trolley wire:

Details
(a) low and medium voltage lines - 1.2 metres
PROVIDED that where an insulated conductor suspended from a bearer wire crosses over a trolley wire the minimum clearance for such insulated conductor shall be 0.6 metre.
(b) high voltage lines up to and including 11,000 volts - 1.8 metres
(c) high voltage lines above 11,000 volts - 2.5 metres
(d) extra-high voltage lines - 3.0 metres

5(2) In any case of a crossing referred to in sub-rule (1), whoever lays his line later in time, shall provide the clearance between his own lines and the line which will be crossed in accordance with the provisions of said sub-rule: 

PROVIDED that if the later entrant is the owner of the lower line and is not able to provide adequate clearance, he should bear the cost for modification of the upper line so as to comply with this rule.

79. Clearance from buildings of low and medium voltage lines and service lines

(1) Where a low or medium voltage over-head line passes above or adjacent to or terminates on any building, the following minimum clearances from any accessible point, on the basis of maximum sag, shall be observed:-

(a) for any flat roof, open balcony, verandah roof and lean-to-roof-

  1. when the line passes above the building a vertical clearance of 2.5 metres from the highest point; and
  2. when the line passes adjacent to the building a horizontal clearance of 1.2 metres from the nearest point, and

(b) for pitched roof-

  1. (i) when the line passes above the building a vertical clearance of 2.5 metres immediately under the lines, and
  2. (ii) when the line passes adjacent to the building a horizontal clearance of 1.2 metres.

(2) Any conductor so situated as to have a clearance less than that specified in sub-rule (1) shall be adequately insulated and shall be attached 6* * * at suitable intervals to a bare earthed bearer wire having a breaking strength of not less than 350 kg.

(3) The horizontal clearance shall be measured when the line is at a maximum deflection from the vertical due to wind pressure.

7Explanation-For the purpose of this rule, expression "building" shall be deemed to include any structure, whether permanent or temporary .

80. Clearance from buildings of high and extra-high voltage lines

(1) Where a high or extra-high voltage over-head line passes above or adjacent to any building or part of a building it shall have on the basis of maximum sag a vertical clearance above the highest part of the building immediately under such line, of not less than-

Details
(a) for high voltage lines up to and including 33,000 volts - 3.7 metres
(b) for extra-high voltage lines - 3.7 metres plus 0.3 metre for every additiona1 33,000 volts or part thereof

(2) The horizontal clearance between the nearest conductor and any part of such building shall, on the basis of maximum deflection due to wind pressure, be not less than

Details
(a) for high voltage lines up to and including11,000 volts - 1.2 metres
(b) For high voltage lines above 11,000 volts and up to and including 33,000 volts - 2.0 metres
(c) for extra-high voltage lines - 2.0 metres plus 0.3 metre for every additional 33,000 volts or part thereof

6Explanation - For the purpose of this rule expression "building" shall be . deemed to include any structure, whether permanent or temporary. 8Various clearances such as vertical, horizontal and ground clearance shall be considered as per the sketch in Annexure XVI.

81. Conductors at different voltages on same supports

Where conductors forming parts of systems at different voltages are erected on the same supports, the owner shall make adequate provision to guard against danger to linesmen and others from the lower voltage system being charged above its normal working voltage by leakage from or contact with the higher voltage system; and the methods of construction and the clearances between the conductors of the two systems shall be subject to the prior approval of the Inspector.

982. Erection of or alteration to buildings, structures, flood banks and elevation of roads

(1) at any time subsequent erection an (whether covered with insulating material bare), person proposes erect a new building structure flood bank raise road level carry out. other type whether permanent temporary make in upon road, addition alteration, and contractor whom employs out erection, shall, such work, building, structure, bank, .additions alterations, thereto would, during after construction, result contravention provisions rules 77 79 80 give notice writing his intention supplier shall furnish therewith scale drawing showing proposed scaffolding required construction.

(2) (a) On receipt referred sub-rule (1) otherwise, examine under reference was lawfully laid liable pay cost so, send a notice without undue delay, to such person together with an estimate of the cost of expenditure likely to be incurred to so alter the overhead line and require him to deposit, within 30 days of the receipt of the notice with the supplier, the amount of estimated cost. within 30 days supplier, amount estimated cost.

(b) If the person referred to in sub-rule (1) disputes the supplier's estimated cost of alteration of the over-head line or even the responsibility to pay such cost, the dispute may be referred to the Inspector by either of the parties whereupon the same shall be decided by the Inspector.

(3) No work upon such building, structure, flood bank, road and addition or alteration thereto shall be commenced or continued until the Inspector has certified that the provisions of rules 77,79 or 80 are not likely to be contravened either during or after the aforesaid construction:

PROVIDED that the Inspector may, if he is satisfied that the over-head line has been so guarded as to secure the protection of persons or property from injury , or risk of injury , permit the work to be executed prior to the alteration of the over-head line, or, in case of temporary addition or alteration, without alteration of over-head line.

(4) On receipt of the deposit, the supplier shall alter the over-head line within one month of the date of deposit or within such longer period as the Inspector may allow and ensure that it shall not contravene the provisions of rules 77, 79 or 80 either during or after such construction.

(5) In the absence of an agreement to the contrary between the parties concerned, the cost of such alteration of the over-head line laid down shall be estimated on the following basis, namely-

(a) the cost of additional material used on the alteration giving due credit for the depreciated cost of the material which would be available from the existing line;

(b ) the wages of labour employed in effecting the alteration;

(c) supervision charges to the extent of 15 per cent of the wages mentioned in clause (b ); and

(d) any charges incurred by the supplier in complying with the provisions of section 16 of the Act in respect of such alterations.

(6) Where the estimated cost of the alteration of the over-head line is not deposit the supplier shall be considered as an aggrieved party for the purpose of this rule.

1082A. Transporting and storing of material near overhead lines

(1) No rods, pipes or similar materials shall be taken below or in the vicinity of any bare overhead conductors or lines if they are likely to infringe the provisions for clearances under rules 79 and 80, unless such materials are transported under the direct supervision of a competent person authorised in this behalf by the owner of such over-head conductors or lines.

(2) Under no circumstances rods, pipes or other similar materials shall be brought within the flash over distance of bare live conductors or lines; and

(3) No material or earth work or agricultural produce shall be dumped or stored or trees grown below or in the vicinity of bare overhead conductors lines so as to reduce the requisite safety clearances specified under rules 79 and 80.

83. Clearance-general

11(1) For the purpose of computing the vertical clearance of an over-head line, the maximum sag of any conductor shall be calculated on the basis of the maximum sag in still air and the maximum temperature as specified by the State Government under rule 76(2)( d). Similarly, for the purpose of computing any horizontal clearance of an over-head line, the maximum deflection of any conductor shall be calculated on the basis of the wind pressure specified by the State Government under rule 76 (2)(a) 12or may be taken as 35°, whichever is greater.

13(2) No blasting for any purpose shall be done within 300 metres from the boundary of sub-station or from the High Voltage or Extra High Voltage electric supply lines or tower structure without the consultation of the owner of such sub-station or electric supply lines or tower structures and in case of mining leasehold area, without the written Permission of the Chief Inspector of Mines or the Electrical Inspector of Mines.

84. Routes-proximity to aerodromes

Over-head lines shall not be erected in the vicinity of aerodromes until the aerodromes authorities have approved in writing the route of the proposed lines.

85. Maximum intervals between supports

All conductors shall be attached to supports at intervals not exceeding the safe limits based on the ultimate tensile strength of the conductors and the factor of safety prescribed in rule 76:

PROVIDED that in the case of over-head lines carrying low or medium voltage conductors, when erected in, over, along or across any street, the interval shall not, without the consent in writing of the Inspector, exceed 65 metres.

86. Conditions to apply where telecommunication lines and power lines are carried on same supports

(1) Every overhead telecommunication line erected on supports carrying a power line shall consist of conductors each having a breaking strength of not less than 270 kg.

(2) Every telephone used on a telecommunication line erected on supports carrying a power line shall be suitably guarded against lightning and shall be provided by cut-outs.

(3) Where a telecommunication line is erected on supports carrying a high or extra-high voltage power line arrangement shall be made to safeguard any person using the telephone against injury resulting from contact, leakage or induction between such power and telecommunication lines.

87. Lines crossing or approaching each other

(1) Where an over-head line crosses or is in proximity to any telecommunication line, either the owner of the over-head line or the telecommunication line, whoever lays his line later, shall arrange to provide for protective devices or guarding arrangement, in a manner laid down in the Code of Practice or the guideline prepared by the Power and Telecommunication Co-ordination Commitee and subject to the provisions of the following sub-rules.

(2) When it is intended to erect a telecommunication line or an over-head line which will cross or be in proximity to an over-head line or a telecommunication line, as the case may be, the person proposing to erect such line shall give one- month ' s notice of his intention so to do along with the relevant details of protection and drawings to the owner of the existing line.

14(3) Where an over-head line crosses or is in proximity to another overhead line, guarding arrangements shall be provided so as to guard against the possibility of their coming into contact with each other. Where an over-head line crosses another over-head line, clearances shall be as under :

1Minimum clearances in metres between lines when crossing each other

S.No Nominal System Voltage 11-66 KV 110-132KV 220KV 400KV 800KV
1. Low and medium 2.44 3.05 4.58 5.49 7.94
2. 11-66 KV 2.44 3.05 4.58 5.49 7.94
3. 110-132KV 3.05 3.05 4.58 5.49 7.94
4. 220KV 4.58 4.58 4.58 5.49 7.94
5. 400KV 5.49 5.49 5.49 5.49 7.94
6. 800KV 7.94 7.94 7.94 7.94 7.94

PROVIDED that no guardings are required when an extra-high voltage line crosses over another extra-high voltage, high voltage, medium or low voltage line or a road or a tram subject to the condition that adequate clearances are provided between the lowest conductor of the extra-high voltage line and the topmost conductor of the overhead line crossing underneath the extra-high voltage line and the clearances as stipulated in rule 77 from the topmost surface of the road is maintained.

(4) A person erecting or proposing to erect a line which may cross or be in proximity with an existing line, may normally provide guarding arrangements on his own line or require the owner of the other over-head line to provide guarding arrangements as referred to in sub-rule (3).

(5) In all cases referred to in the preceding sub-rules the expenses of providing the guarding arrangements or protective devices shall be borne by the person whose line was last erected.

(6) Where two lines cross, the crossing shall be made as nearly at right angles as the nature of the case admits and as near the support of the line as practicable and the support of the lower line shall not be erected below the upper line:

15PROVIDED that the angle of crossing of power lines shall not be less than 60 degrees.

(7) The guarding arrangements shall ordinarily be carried out by the owner of the supports on which it is made and he shall be responsible for its efficient maintenance.

(8) All work required to be done by or under this rule shall be carried out to the satisfaction of the Inspector.

88. Guarding

(1) Where guarding is required under these rules the provisions of sub-rules (2) to (4) shall apply.

(2) Every guard-wire shall be connected with earth at each point at which its electrical continuity is broken.

(3) Every guard-wire shall be an actual breaking strength of not less than 635 kg. and if made of iron or steel, shall be galvanised.

(4) Every guard-wire or cross-connected system of guard-wires, shall have sufficient current-carrying capacity to ensure the rendering dead, without risk of fusing of the guard-wire or wires till the contact of any live-wire has been removed.

******* Diagram

(5) Lines crossing trolley-wires-In the case of crossing over a trolley-wire the guarding shall fulfill the following conditions, namely:-

(a) where there is only one trolley-wire, two guard-wires shall be erected as in diagram A;

(b) where there are two trolley-wires and the distance between them does not exceed 40 cms., two guard-wires shall be erected as in diagram B;

(c) where there are two trolley-wires and the distance between them exceeds 40 cms, but does not exceed 1.2 metres, three guard-wires shall be erected as in diagram C;

(d) where there are two trolley-wires and the distance between them exceeds 1.2 metres, each trolley-wire shall be separately guarded as in diagram D;

(e) the rise of the trolley boom shall be so limited that if the trolley leaves the trolley-wire, it shall not foul the guard, wires; and

(f) where a telegraph-line is liable to fall or be blown down upon an arm, stay-wire or span-wire, and so slide down upon a trolley-wire, guard hooks shall be provided to prevent such sliding.

89. Service-lines from overhead lines

No service-line or trapping shall be taken off an overhead line except at a point of support :

16PROVIDED that the number of trappings per conductor shall not be more than four is case of low and medium voltage connections.

90. Earthing

(1) All metal supports and all reinforced and prestressed cement concrete supports of over-head lines and metallic fittings attached thereto, shall be permanently and efficiently earthed. For this purpose a continuous earth wire shall be provided and securely fastened to each pole and connected with earth ordinarily at three points in every km. the spacing between the points being as nearly equidistant as possible. Alternatively, each support and the metallic fitting' attached thereto shall be efficiently earthed.

17(1A) Metallic bearer wire used for supporting insulated wires of low and medium voltage over-head service lines shall be efficiently earthed or insulated.

(2) Each stay-wire shall be similarly earthed unless an insulator has been placed in it at a height not less than 3.0 metres from the ground.

91.Safety and protective devices

1) Every over-head line (not being suspended from a dead bearer wire and not being covered with insulating material and not being a trolley-wire) erected over any part of a street or other public place or in any factory or mine or on any consumers premises shall be protected with a device approved by the Inspector for rendering the line electrically harmless in case it breaks.

(2) An Inspector may by notice in writing require the owner of any such over-head line wherever it may be erected to protect it in the manner specified in sub-rule (1).

1(3) The owner of every high and extra-high voltage over-head line shall make adequate arrangements to the satisfaction of the Inspector to prevent unauthorised persons from ascending any of the supports of such over-head lines which can be easily climbed upon without the help of a ladder or special appliances. Rails, reinforced cement concrete poles and pre-stressed cement concrete poles without steps, tubular poles, wooden supports without steps, I-section and channels shall be deemed as supports which cannot be easily climbed upon for the purpose of this rule.


COMMENTS

Over head electric wires carrying heavy load of electric energy are highly dangerous , and if any human being or animals comes into contact with the same, the consequences are fatal. Hence great care and caution are expected of the Electricity Board in laying, installing and maintaining over-head wire so that the wire do not fall down. If such a thing happens a prima facie inference can be drawn that there has been carelessness or negligence on/the part of the Electricity Board in transmitting electric energy or in maintaining the transmission lines.- Nirmala v. T.N. Electricity Board AIR 1984 Mad 201


92. Protection against lightning

(1) The owner of every overhead line 18sub-station or generating station which is so exposed as to be liable to injury from lightning shall adopt efficient means for diverting to earth any electrical surges due to lightning.

19(2) The earthing lead for any lightning-arrestor shall not pass through, any iron or steel pipe, but shall be taken as directly as possible from the lightning-arrestor to a separate earth electrode and/or junction of the earth mat already provided for the high and extra high voltage sub-station subject to the avoidance of bends wherever practicable.

Note: A vertical ground electrode shall be connected to this junction of the earth mat.

93. Unused overhead lines

(1) Where an over-head line ceases to be used as an electric supply line, the owner shall maintain it in a safe mechanical condition in accordance with rule 76 or shall remove it.

(2) Where any overhead line ceases to be used as an electric supply line, an Inspector may, by a notice in writing served on the owner, require him to maintain it in a safe mechanical condition or to remove it within fifteen days of the receipt of the notice.


1 Substituted by GSR 466, dt.18-7-1991, w.e.f.17-8-1991. 
2 Inserted by GSR 730, dt.7-9-1989,w.e.f.30-9-1989. -
3 Substituted vide GSR 274, dt. 10-7-2002, w .e.f. 20-7-2002. 
4 Renumbered by GSR 528, dt.11-7-1986, w.e.f. 19-7-1986.
5 Inserted by GSR 528,dt.11-7-1986,w.e.f.19-7-1986. 
6 Words "by means clips" omitted by GSR, dt. 28-3-1966, w.e.f. 9-4-1966. 
7 Added by GSR 844, dt. 31-7-1985, w.e.f. 7-9-1985. 
8 Inserted vide GSR 793(E), w.e.f. 4-12-2002. 
9 substituted by GSR 1723, dt. 21-11-1977, w.e.f. 31-12-1977. 
10 Inserted by GSR 358, dt. 30-4-1987, w.e.f. 9-5-1987.
11 Existing sec. 83 renumbered as sub-sec. (1) thereof vide GSR 793(E), dt. 3-12-2002.
12 Inserted by GSR 1723, dt. 21-11-1977, w.e.f. 31-12-1977.
13 Inserted vide GSR 793(E), d t. 3-12-2002. 
14 Substituted by GSR 256, dt. 28-2-1983, w .e.f. 26-3-1983.
15 Inserted vide GSR 274, dt. 10-7-2002, w .e.f. 20-7-2002. 
16 Inserted by GSR 45, dt.1-1-1993, w.e.f. 23-1-1993.
17 Inserted by GSR 732, dt.18-6-1985, w.e.f. 3-8-1985.
18 Inserted by GSR 466,dt.18-7-1991,w.e.f.17-8-1991.
19 Substituted by GSR 1050, dt. 22-10-1985,w.e.f. 9-11-1985.

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