Earthing System Components – Part One


In Article " How to Select the Best Earthing System ", I explained the following points:

  • Criteria for Selection of the Best Earthing System,
  • Steps for Choosing the Best Earthing System.


Today I will explain The Construction and Components of Earthing Systems as follows.








Earthing System Components

Earthing system in an installation is normally comprised of the following components:

  1. Earth wells and accessories,
  2. Earthing grid conductors,
  3. Marshalling earth buses (earthing distribution buses),
  4. Earthing wires and cables.








1- Earth Wells and Accessories

  • Earth wells for a specific building or installation are actually the location, where the pure zero potential is provided and practically act as drain pits for any rush current which accidentally appears in the earthing system grid in the event of an earth fault (connection of electrical live parts to the earthing system).
  • There are different types of components can be used to set up an earth well Depending on the following factors:

  1. Soil conductivity of the location in which the earth wells are installed,
  2. The required technical specifications of the earthing system.


  • However, the prime components and accessories of an earth well will be:


  1. Earth Rod,
  2. Earth Plate,
  3. Earthing Clamp,
  4. Earthing Rod Coupling,
  5. Earthing Rod Tip,
  6. Earthing Rod Driving Head with driving sleeve,
  7. Earth Access Pit,
  8. Earth Pit Cover,
  9. Earth Enhancement Materials.













1.1 Earth Rods

  • Depending on the design for a specific earth well, a number of rods are driven into the ground by means of hammering or driving to form the main earthing electrode in the earth well.
  • The earth rod have three types:

  1. Non-Sectional Ground Rods: have unthreaded top.
  2. Sectional Ground Rods: have externally threaded top.
  3. Sectional Ground Rods: have internally threaded top.






Notes:

  • In Cases where two or more earth rods are to be driven, the individual rods are coupled to each other by means of “earth rod coupling”.
  • Ground rods coupling process are used to help reduce ground resistance in poor soils such as sand and gravel.
  • Doubling rod length theoretically reduces ground resistance about 40%.



1.1.1 Methods for Driving Earth Rod into Ground

Two methods are used to drive the rod into the ground:

  1. Hammering: by using a hammer, a drive stud and rod tip.
  2. Driving: by using a Driving Hammer Tool and Ground Rod Drive Bit or using a Driving Hand Tool.








Notes:

  • During the hammering or driving of rod into the ground, and to protect the earth rod against impact of hammering, a “driving head” is screwed onto the top of the rod.
  • For easy and convenient driving of the earth rod into the ground an earth rod tip with sharp point is screwed to the first rod.
  • Earth rods are used in installation of plain earthing well where, based on design specification of the earthing system, the carbon bedding is not necessary and applicable.



1.1.2 Earth Rod Material


  • UL467- 9.2.1 states that the solid rod electrode of copper or other suitable non-ferrous metal, or a solid rod electrode of iron or steel with a copper or other suitable non-ferrous metal or stainless steel jacket, shall have a diameter not less than ½ inch thick.
  • Also, UL467-9.2.2 states that the stainless steel jacket shall not be less than 0.015 inches thick at any point.
  • And UL467-9.2.6 states that the stainless steel jacket mentioned above on a stainless steel rod shall be formed of an austenitic stainless steel of the 18% chromium, 8% nickel type. And stainless steel ground rods are used in corrosive soil conditions.
  • Usually in Europe and Middle East, Earthing rod and the associated accessories (coupling, tip and head) are made of both steel and copper. A steel core, coated with pure copper to the appropriate thickness, provides the sufficient rigidity for the earthing rod to help driving it straightly into the ground without any harm and bending. The copper coating of the earth rod provides the sufficient conductivity for the earthing system.



1.2.3 Earth Rod Dimensions


a- Diameter:

  • Depending on the design specification of the earthing system and the corresponding earthing wells, various earth rods of different dimensions would be incorporated.
  • As per UL467- 9.2.1, the solid rod electrode shall have a diameter not less than ½ inch thick.
  • In Europe and middle east, The range of diameter for the earth rods vary from 13 mm to 25mm (13mm,16mm, 20mm, 25mm).



b- Length:

Different lengths of earthing rods are used in design and installation of earth wells, The standard lengths are:

  • In North America: 2, 3, 5, 8 and 10 feets.
  • In europe and middle east: 1200mm, 2400 mm (2 × 1200 mm), 3600 mm (3 × 1200 mm) and 4800 mm (4 × 1200 mm).









1.2 Earth Plate

In earth wells with carbon beddings, earthing plates are normally used instead of earthing rods. The earth plate is made of copper and shaped in the following forms:

  1. Flat rectangular copper plate,
  2. Perforated rectangular copper plate (Earth Mat).






Copper ground plates are used instead or with the ground rods in the following situations:

  • In areas having little or no top soil,
  • If it is required to enhance ground grid systems,
  • In conjunction with earth enhancements materials.


For securing good electrical connections with the ground plate, ground plate use:

  1. One cable connector,
  2. Two dual cable connectors,
  3. 18 or 24 inches (depending on the plate size) copper conductor exothermically welded to the plate cable connectors






Earth Plate Size:

The common sizes of ground plates are:

  • In North America: 18 x 18 inches or 24 x 24 inches.
  • In Europe:

  1. The flat rectangular earth plate is normally 100 × 100 × 3 mm.
  2. The standard cross section area for the copper rod or copper strips used in construction of the perforated rectangular earth plate is normally 75 sq-mm.









Differences between Earth rods and Earth Plates

Earth rods and plates or any combination thereof can be used to achieve an effective earth depending on the site conditions. The main difference between Earth rods and Earth Plates is as follows:

  • Earth rods take advantage of lower resistivity soils at greater depths than normal excavation will allow.
  • While, Earth plates are used to attain an effective earth in shallow soils with underlying rocks or in locations with large amounts of buried services. They can also provide protection at potentially dangerous places eg HV switching positions.










1.3 Earthing Clamp

  • Earthing grid conductors are connected to the earth rods, already driven into the ground, by means of earthing clamps.
  • This Connection between earth rod and Earthing grid conductors is essentially made by tightly clamping of the grid conductor to the rod by one of the two following methods:

  1. Mechanical Clamps,
  2. Exothermic Welding Clamping.



1- Mechanical Clamps:





  • They are Used Where permanent connections are not appropriate, mechanical clamps offer the ideal solution. These are typically used on smaller scale installations where periodic disconnection for testing is required.
  • The mechanical earhing clamp may come with one bolt or two bolts, the two bolts give more good electrical connection with the earh rod.
  • Mechanical Earthing clamps and associated bolts nuts, washers, etc. are made of brass, bronze or copper.
  • The mechanical earth clamps sizes shall be selected to accommodate the diameters of earh rod and grounding conductors.



Types Of Mechanical Earthing Clamps:

  1. Light duty type: this type is acceptable for electrical grounding but not for lightning protection.
  2. Heavy duty type: this type is acceptable for lightning protection and requires 1-1/2 inches of surface contact between conductor and earth rod.



2- Exothermic Welding Clamping:





  • A simple, self-contained method of forming high quality electrical connections which requires no external power or heat source. Connections are made using the high temperature reaction of powdered copper oxide and aluminium.
  • Exothermic Welding connections allow conductors to carry higher currents than other types of connections. They will never loosen, are highly conductive and have excellent corrosion resistance.
  • The Exothermic Welding will be explained later in separate aricle.










1.4 Earthing Rod Coupling


  • In some cases, Depending on the design for a specific earth well, there is need to drive two or more earth rods into the ground, the individual rods are coupled to each other by means of “earth rod coupling”.
  • There are three types of rod couplers according to the used type of ground rods as follows:
  1. Unthreaded Coupler for Non- sectional ground rods,
  2. Threaded Coupler for sectional ground rods externally threaded,
  3. Coupling Dowel for sectional ground rods internally threaded.




  • The coupling material is essentially the same as the material for the earth rod with respect to the rigidity and the required conductivity. 
  • Earth rod coupling shall have the same diameter of the earth rod.









1.5 Earth Rod Tip





  • The earth rod tip is used for easy and convenient driving of the earth rod into the ground because it secures a sharp head for the first rod driven into ground.
  • The earth rod tip material is not necessarily the same as the earth rod itself, as only a rigid quality is essentially required for the tip other than conductivity. Therefore the earth rod tip is primarily made of steel with slight coating of the copper for conductivity purpose as well as protection against corrosion reasons.
  • Earth rod tip shall have the same diameter of the earth rod.










1.6 Earth Rod Driving Head with Driving Sleeve

During the hammering or driving of rod into the ground, and to protect the earth rod against impact of hammering, a “driving head” is screwed onto the top of the rod with a driving sleeve.




  •  So, the main function of driving sleeve is to prevent Mushrooming top of ground rod while driving into ground.
  • And, the main function of a driving head stud is to prevent damage to the coupler or ground rod threads when driving the ground rods.
  • The driving head material is not necessarily the same as the earth rod itself, as only a rigid and robust quality is essentially required for the driving head to withstand the impact of hammerings. Driving head is practically discarded when the earth rods are all driven and installed in the ground.







In the next Article, I will continue explaining the Earthing Systems Components. Please, keep following.









1 comment:

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