1. MUHAMMADALI MC SDE(KAM) KANNUR EARTHING

2. O BJECTIVES OF EARTHING  To reduce the cross talk and noise  To afford reliable path for circuits involved in switching  To afford return path for conductor in some telegraph ckt  To protect costly apparatus & person against foreign voltage and leakage current  To protect building & equipment from lightning strikes Requirement of Effective Earthing 1. The resistance to the earth must be minimum 2. The earth electrode must provide as much area of contact as possible to reduce resistance 2 enjoy this killing deal from Shopclues:

3. 3. The electrode buried in the ground must be Having Good Electrical conductivity Immune to Corrossive action of soil Sufficient mechanical strength Inert, must not be source of galvanic current 4. The resistance of earth connection must remain within specified limit through out the season. Classes of Earthing: 1. Service Earthing 2. Protective Earthing 3

4. Service Earthing:  Equipment Earthing for Switching, Transmission, measuring equipments etc.  Should have low DC resistance  If any current flows through service earthing, a potential difference will be developed across earth. This will introduce interference in form of noise Protective Earthing:  Protection against Excessive current  Lightning Protection against excessive voltage  It should have low resistance  Ability to flow sufficient current within short time 4

5.  Ability to carry anticipated value of overcurrent w/o bursting and over heating  Ability to prevent hazardous potential difference  Ability to withstand corrossive action of soil  Earth to lightning protection must have low surge impedence Earth Electrode Material: 1. Earth Resistance should be < 0.5 ohm 2. Copper is good electrical conductor, it cause high corrosion 3. So Galvanised Steel / Copper is used 5

6. S PIKE EARTHING  Consists of metal rods / pipes driven vertically into ground  Consists of 20 nos of 25mm / 38mm diameter GI pipe  Each GI with 275 or 375 cm length  Spacing between adjacent electrode shouldn’t be less than 375cm (atleast minimum 250cm)  Spike should be connected by bare tinned copper 70cm 30cm 6

7. L EAD STRIP ELECTRODE EARTHING  Lead strip is used  51mm vide 6gms / cm square  Buried at a depth of 60 to 90 cm length  Laid in one continous length 2450cms or two lengths of 1225cms with min 250cm apart & 152mm overlapping  Spike should be connected by bare tinned copper 250cm 152mm 7

8. E ARTH PLATE ELECTRODE EARTHING  Galvanised Iron plates 4nos  600mm x 600mm 6.5mm thickness plates  Placed vertically and diagonally opposite ends  Pit of 185cmx 185cm square with 3m depth  Connected with strip of 50mm x 3mm area RING EARTHING  150cm depth in ordinary soil  60 to 90cm depth in rocky soil with 30cm width  GI strip 50mm x 3mm laid in trench SAFE EARTHING ELECTRODE EARTHING (SEE) Readymade kit supplied by ASHLOK  8

9. C HOICE OF EARTHING SYSTEMS Spike System : Adequate space with subsoil suitable for driving pipes Lead Strip : Space available with rocky strata Plate system : Space is not available Common Earthing  Not possible to ensure no electrical coupling between earth systems  Risk of Fire etc due to potential difference  Current may flow through structure or between systems Earthing of wave guide: Earthed at top, botom, intervals by kit provided by manufacturer 9

10. P OINTS TO BE NOTED 1.Earth Resistance: Should be less than 0.5 ohm 2.Measurement : Every six months For lightning area it is every month & use copper instead of GI 3.Coiling of conductor should be avoided 4.Bending radius minimum 1 meter 5.Should not pass through metalic conduits 6.All joints should be water proof 7.Aviation lamp, lightning arresters to be looped to tower Ring earth. 10

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