Earthing System Components – Part Three


In Article "  Earthing System Components – Part One ", I indicated that:





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

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.



Also in this Article, I explained the first six items of Earth Wells and Accessories; Earth Rod, Earth Plate, Earthing Clamp, Earthing Rod Coupling, Earthing Rod Tip and Earthing Rod Driving Head with driving sleeve.


And in Article " Earthing System Components – Part Two ", I explained the last three items of Earth Wells and Accessories; Earth Access Pit, Earth Pit Cover and Earth Enhancement Materials.



Today I will continue explaining other Earthing Systems components as follows.


You can preview the following Articles for more info:




2- Earthing Grid Conductors

All electrical earth wells in a specific residential, commercial and industrial installation should essentially be interconnected to plant earthing systems with cables, wires and tapes that form the main earthing grid.


First: Different Types of ground Grid Conductors:

Interconnecting conductors used for the grid are in the following forms:

1- Cable and wire system

The available conductors may be soft-drawn (copper wire that has been heat treated) or hard-drawn (copper wire that has not been annealed after drawing), the available grounding conductors are in the following forms:


1.1 Stranded Copper Conductors:






  • Concentric Lay Soft-Drawn Bare Copper,
  • Green Insulated Conductors (Concentric Lay Soft-Drawn Bare Copper with PVC sheath or THW insulation),
  • Tinned stranded copper conductor.



1.2 Solid Copper Conductors:





  • Solid Single Soft-Drawn Bare Copper,
  • Solid Single Soft-Drawn Bare Tinned Copper.



1.3 Flexible Copper Conductors: used as flexible earth bonding leads





  • Bare copper round braids,
  • Tinned copper round braids.



2- Flat tape system:


it give Low impedance than equivalent sized round conductor and it will be in the following forms:








  • Bare copper tapes,
  • Tinned copper tapes,
  • Bare Copper Flat Braid Conductors,
  • Tinned Copper Flat Braid Conductors.


Note:

There are other types of grid conductors used especially for lightning protection system and will be explained later in lightning protection system Articles.


Second: Selection criteria for the best grounding conductor for certain case:

There are two basic criteria for grounding conductor selection:


1- Physical Characteristics

The physical characteristics of the conductor must be of a robust nature, sufficient for the environment as follows:

  • The most common ground conductor is a soft drawn, stranded copper conductor which used for direct buried grid in dry and noncorrosive grounds.
  • Flat copper strip / tape is also popular because it offers a large surface area and usually used for direct buried grid in dry and non-corrosive grounds (soils).
  • PVC-Covered copper strip conductor: for direct buried grid in wet or corrosive ground.
  • Single core stranded copper conductor with PVC sheath: for direct buried grid in wet or corrosive grounds.


Note:

When site conditions are corrosive towards copper (eg. sulphurous soil), a tinned copper conductor is often the first choice.


2- Maximum Fault Current

  • The cross sectional area of the conductor must be of sufficient size, so that it shall successfully conduct the maximum fault (surge) current for a period, which allows the operation of protection equipment (or the dissipation of this energy).
  • In some circumstances, the maximum fault current for the installation is small. While a conductor of correspondingly small size could be used, a minimum cross section often set by the governing authority or applicable Standards body (to minimize potential damage likely to occur from any future excavation on the site), is applied.
  • Where higher fault conditions exist, the conductor size is determined by considering the circumstances required to avoid fusing (melting) the conductor. The accepted industry Standard is IEEE 80, Guide for Safety in Substation Grounding.



Third: Ground Grid Conductors sizing

  • Ground Grid Conductors sizing will be explained later in the Articles for grounding system design calculations.







3- Marshaling Earth Bus





  • To provide easy access to the earthing grid, particularly to make proper and convenient connections of the equipment to the grid, several common connection points in the form of a flat bar of copper material are established and erected through out the grid and referred to as “earthing marshalling points” or “earthing marshalling bus”, or simply as “earth bus”.
  • The main incoming earthing cable connected to the earth bus is branched off from the main earthing grid.
  • The outgoing earthing cables, connected to the earth bus in one end, shall be connected to the corresponding equipment on the other end.
  • All the connections of the main incoming and outgoing earth cables shall be made to the earth bus by means of appropriate:




  1. Cable lugs the compression type and zink coating, using bolts, nuts, flat washers and spring washers for well-tight connections,
  2. Exothermic Welding process.








4- Earthing Wires (Cables)

  • Connections between the marshalling earth buses and the equipments are carried out by means of single wires or cables of appropriate size, which are referred to as “earthing wire”, or “earthing link”. The connection between the earthing buses and the earthing grid is also made by means of earthing cables.
  • Connections of earthing wires (cables) on both ends is made by appropriate:





  1. Cable lugs the compression type and zink coating, using bolts, nuts, flat washers and spring washers for well-tight connections,
  2. Exothermic Welding process.


1- earthing wires (cables) Types

  • Earthing wires and cables are used either bare or PVC-covered (preferably bare) and are normally single core of the different cross section area, depending on the design specification.







2- Earthing wires (cables) sizing

  • The common range of the cable size used is 16mm2, 25mm2, 35,50mm2 and 70mm2. Earthing wires (cables) of smaller and higher size could be used depending on the design specification and requirements.
  • Earthing wires (cables) sizing will be explained later in the Articles for grounding system design calculations.





In the next Article, I will explain The Electrical Properties of Earthing Electrodes. Please, keep following.





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