Quick Reference -Earthing


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.

 

OVERLAPING OF EARTHING STRIP

Size of Earthing Strip

Minimum Over Laping

20×3

20MM

20×6

20MM

25×3

25MM

25×6

25MM

32×6

25MM

40×5

50MM

40×6

50MM

50×6

50MM

50×10

50MM

75×6

50MM

75×10

50MM

 

NO’S AND SIZE OF NUT BOLT FOR JOINTING EARTHING STRIP

Size of Earthing Strip

Minimum Nut Bolt Required

Minimum Size of Nut Bolt

20×3

2 NO’S

8X25MM

20×6

2 NO’S

8X25MM

25×3

2 NO’S

8X25MM

25×6

2 NO’S

8X25MM

32×6

2 NO’S

8X25MM

40×5

4 NO’S

8X25MM

40×6

4 NO’S

8X25MM

50×6

4 NO’S

10X25MM

50×10

4 NO’S

10X25MM

75×6

4 NO’S

10X25MM

75×10

4 NO’S

10X25MM

 

Weight of G.I. wire  (Steel Tube India)

Gauge Gms.

mm

Weight Kg / Meter.

4

5.892

0.216

6

4.876

0.148

8

4.064

0.103

10

3.251

0.066

12

2.641

0.045

14

2.032

0.026

16

1.625

0.017

 

Weight of G.I Flat Strip

Sizes in (HxW)

Kgs/Per meter

Application

20×3 mm

0.49

Lighting Arrestor

20×6 mm

0.98

PLC Panel

25×3 mm

0.6

 

25×5 mm

0.97

 

25×6 mm

1.3

Control & Relay Panel

32×5 mm

1.21

Lighting Panel & Local Panel

32×6 mm

1.625

Distribution Board

40×3 mm

0.964

Motors 5.5kw-55Kw

40×5 mm

1.476

 

40×6 mm

1.92

HT switchgear, structures, cable trays & fence, rails, gate and steel column

50×3 mm

1.28

50×5 mm

1.92

50×6 mm

2.56

50×10 mm

4

Transformers Substations

62×6 mm

3.07

65×10 mm

5.2

75×10 mm

6

75×12 mm

7.2

 

Method for Installation of Cable Tray-(PART 2)


  • Horizon Tee Support: NEMA Standard
  • Supports for horizontal tee fittings should be located at a distance, no greater than 610 mm (24″) from each end of the fitting on the attached ladder. Fitting should also be supported once on each side rail. For 305 mm (12″) radius tees, place supports no greater than 610 mm (24″) from each end of the fitting on the attached ladder.

1

  • Horizon Cross Support: NEMA Standard
  • Supports for horizontal cross fittings should be located at a distance, no greater than 610 mm (24″) from each end of the fitting on the attached ladder.
  • Fitting should also be supported once on each side rail. For 305 mm (12″) radius cross, place supports no greater than 610 mm (24″) from each end of the fitting on the attached ladder.

2

  • Reducer Support: NEMA Standard
  • Place horizontal supports (2) at a distance no greater than 610 mm (24″) from each end.

3

  • Horizontal Y Support: NEMA Standard
  • Place horizontal supports at a distance no greater than 610 mm (24″) from each of the three openings and at the midpoint of the fitting at 22.5°

 4

  • Vertical Inside / Outside Support: NEMA Standard
  • Vertical cable tray elbows at the top of runs should be supported at each end. At the bottom of runs, they should be supported at the top of the elbow and within 610 mm (24″) of the lower extremity of the elbows. Both Inside and Outside Fittings should be additionally supported at a distance no greater than (24″) from each end.

5

  • Offset Reducing Connection & Tray to Box / Floor Connection:

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(IV) Cable Tray Installation:

  • Ensure that the Cable Tray’s, dimension, elevation and other fittings are properly leveled and that they are coordinated to the other services fixtures.
  • The width of Cable Tray/trunking/ladder should have sufficient width to take the cable without crowding and shall allow for future 25% space. The cables should not be stacked together.
  • If the conductors carried by trays or ladders are of various systems, the ELV and data processing or different insulation, the cable ladder or trays should be separate. Use insulating barriers where it is necessary. However, approval from the engineer is required.
  • Earth continuity shall be ensured throughout the length of the Trays and Trunking
  • Cable Tray Installation on Roof / Floor:
  • Cable tray should not be laid directly on the floor or roof.
  • Cable trays installed on roof shall be supported using Gl brackets or concrete blocks.
  • It should be mounted far enough off the floor or roof to allow drainage of water.
  • The cables to exit through the bottom of the cable tray.
  • Where cable trays are installed in roof or exposed to sunlight, factory made cover shall be fixed to protect the cables from direct sunlight.
  • Cable Trunking runs shall be arranged so that the lid is always on top or side. Lid shall be fixed to the trunking using factory made quick fix type clips.
  • Open ends of the trays / trunkings shall be capped with purpose made end caps.
  • Cable Tray Accessories:
  • Where cutting of the trays is needed, circular saws will be used. Cable tray cut edges will be rasped or welded if it is necessary, galvanized points will be cleaned then it will be sprayed with galvanizing spray immediately.
  • Cut portion of Trays and Trunking, shall be made free of sharp edges by filing and coated with zinc rich and top coat and jointed using fish-plates with bolts and nuts.
  • Any cutting on the cable tray to be done along the solid area and not across the perforation of the cable tray. Burrs needs to be removed and cuts need to be protected with anti-rust galvanized paint to prevent rust.
  • The minimum radius of Cable Tray should equal the minimum bending radius of the cables. Depending on the number of cables to be placed in the system it may be advantageous to use the next highest radius.
  • Installation of splice connectors
  • Splice connectors shall be located as recommended by the manufacturers.
  • Splice joints should be designed and placed so as to maximize the rigidity of the cable tray.
  • Splice connectors shall be attached by round / Hexa head bolts with the nuts and washers located on the outside of the tray or ladder unless otherwise specified by the manufacturer.
  • Thermal expansion splices shall be installed wherever expansion joints occur.

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  • All straight joints, bends and offset connections shall be made neatly using standard fittings (fish plate and coupler). Only when these are inappropriate, fabricated bends/offsets shall be used.

(5) Cleaning of Work Area:.

  • There should be a visual inspection of the trunking from inside side after installation. This is to be sure that it is free from Debris, burrs and waste materials.
  • There are no sharp edges that could cause damage to the cables during installment.
  • Galvanized coating damaged by excessively rough treatment during transit and erection shall be repaired using at least two coats of good quality zinc-rich paint complying with BS 4652.
  • Upon completion of installation of cable trays/trunking in one area, the completed work shall be presented for Inspection and shall be protected by providing polyethylene sheet cover.

(6) Codes and Standards:.

  • IS 4759: Hot-dip zinc coatings on structural steel and other allied products 
  • IS 2629: Recommended Practice for Hot-Dip Galvanizing of Iron and Steel
  • IS 2633: Methods for testing uniformity of coating of zinc coated articles
  • IEC 61537 Cable Management- Cable Tray System and Cable Ladder System
  • BS 4652 Specification for zinc-rich priming paint
  • National Electrical Manufacturers Association (NEMA) Standard

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