Earthing Strip / Wire / Pit Quick Reference (As per CPWD) (Part-2)

EARTHING STRIP /WIRE / PIT QUICK REFERENCE (AS PER CPWD) (PART-2)

Earthing Strip for Sub-Station Equipment

CPWD-TABLE VIII

Type of Installation Earth Electrode Earth Strip Indoor sub-station with HT panel, Transformer capacity up to 1600 KVA, LT panel, D.G Set. Copper Plate 25 x 5 mm Copper Strip Indoor sub-station with HT panel, Transformer capacity above 1600 KVA, LT panel, D.G Set Copper Plate 32 x 5 mm Copper Strip HT Outdoor sub-station Copper Plate 25 x 5 mm Copper Strip LT Indoor sub-station with generator Copper Plate 25 x 5 mm Copper Strip LT switch room with Main LT D.B Copper Plate 20 x 3 mm Copper Strip

Neutral Earthing of Transformers and Generators

CPWD-TABLE VIII

Type of Installation Earth Electrode Earth Strip for Neutral Transformer of capacity up to 1600 KVA Copper Plate 25 x 5 mm Copper strip Transformer of capacity above 1600 KVA Copper Plate 32 x 5 mm Copper strip Generating set of all capacity Copper Plate 26 x 5 mm Copper strip Type of Installation Earth Electrode Earth Strip for Neutral Transformer of capacity up to 1600 KVA Copper Plate 25 x 5 mm Copper strip

Earthing Strip for Bus Trunking and Rising Main

CPWD-TABLE VIII

Type of Installation Material of Main Conductor Earth Strip Bus trunking up to 2500 Amp capacity Copper/ Aluminum 2 No 25 x 5 mm Copper Strip Bus trunking above 2500 Amp capacity Copper/ Aluminum 2 No 32 x 5 mm Copper Strip Bus trunking for generating set and LT panel Copper/ Aluminum 2 No 25 x 5 mm Copper Strip Rising main up to 400 Amp capacity Copper/ Aluminum 2 No 20 x 5 mm Copper Strip Rising main above 400 Amp and up to 800 Amp Copper/ Aluminum 2 No 20 x 3 mm Copper Strip

The Size of Earthing conductors

As per CPWD

Size of phase conductor Size of Earthing conductor of the same material as phase conductor Up to 4 sq.mm. Same size as that of phase conductor Above 4 sq.mm. up to 16 sq.mm. Same size as that of phase conductor Above 16 sq.mm. up to 35 sq.mm. 16 sq.mm. Above 35 sq.mm. Half of the phase conductor

Materials and Sizes of Earth Electrodes

CPWD-TABLE IX

Type of Electrodes Material Size Pipe GI medium class 40 mm dia 4.50 m long (without any joint) Plate (i) GI 60 cm x 60 cm x 6 mm thick (ii) Copper 60 cm x 60 cm x 3 mm thick Strip (i) GI 100 sq. mm section (ii) Copper 40 sq. mm section Conductor (i) Copper 4 mm dia (8 SWG) Note : Galvanization of GI items shall conform to Class IV of IS 4736 : 1986.

Minimum Sizes of Earthing Conductors for Use Above Ground

CPWD- TABLE X

Material and Shape Minimum Size Round copper wire or copper clad steel wire 6 mm diameter Stranded copper wire 50 sq. mm or (7/3.00 mm dia) Copper strip 20 mm x 3 mm Galvanized iron strip 20 mm x 3 mm Round Aluminum wire 8 mm diameter Aluminum strip 25 mm x 3 mm

Minimum Sizes of Earthing Conductors for Use Below Ground

CPWD- TABLE XI

Material and Shape Minimum Size Round copper wire or copper clad steel wire 8 mm diameter Copper strip 32 mm x 6 mm Round galvanized iron wire 10 mm x 6 mm Galvanized iron strip 32 mm x 6 mm

Selection of Type of Earthing Electrodes

As per CPWD

Type of electrode Application GI pipe Internal electrical installations like Distribution Board and Meter Boards (in residential quarters), feeder pillars and poles etc. GI plate (i) For Fire Fighting pumps and water supply pumps. (ii) Lightning conductors. Copper plate Neutral earthing of transformers/ generating sets. Strip/ Conductor Locations where it is not possible to use other types.

Number of Earth Electrodes

As per CPWD

Equipment No of Earthing For neutral earthing of each transformer 2 sets For body earthing of all the transformers, 2 sets HT/LT Panels and other electrical equipment in the Sub-station/ power house For neutral earthing of each generating set 2 sets For body earthing of all the generating sets, 2 sets LT panels, other electrical equipment in the generator room

Size of protective conductor

As per CPWD

Size of phase conductor Size of protective conductor of the same material as phase conductor Up to 16 sq.mm. Same as Phase Conductor Size 16 to 35 sq.mm. 16 sq.mm. 35 sq.mm Half Size of Phase Conductor

Earthing Points

As per CPWD

Earthing Description Location for Earth Electrodes Normally an earth electrode shall not be located closer than 1.5 m from any building. Installation of Pipe Pipe electrode shall be buried in the ground vertically with its top at not less than 20 cm below the ground level Installation of Plate Plate electrode shall be buried in ground with its faces vertical, and its top not less than 3.0 m below the ground level. The strip or conductor The strip or conductor electrode shall be buried in trench not less than 0.5 m deep More Earthing Electrode When more than one electrode (plate/pipe) is to be installed, a separation of not less than 2 m shall be maintained between two adjacent electrodes. Earthing Electrode If the electrode cannot be laid in…