Types of grounding electrodes
Types of grounding electrodes
1) Rod electrodes
2) Plate electrodes
3) Pipe electrodes
4) Earth lattice
1 Rod electrodes
Types of earth rods
Types of earth rods
1) Solid copper earth rods
2) Copper bonded steel earth rods
3) Galvanized Steel earth rods
4) Stainless steel earth rods
Solid copper earth rods
It is made from high conductivity hard drawn copper
Advantages
It is used for soil with high moisure and salt content and is very corrosive
It is used where high fault currents are expected .
Disadvantages
The solid copper is a ductile metal that will often bend when driven into soil so it is not suitable for use when a deep driving into the ground is needed
Solid copper earth rods are high expensive compared to other types of earth rods
Copper bonded steel earth rods
it is made by electroplating 99.9% pure electrolytic copper (with thickness not less than 250 microbs) onto a low carbon high tensile steel bar .
The copper layer is moleculary bonded to the steel bar so it will not tear or slip when driven into the ground.
Advantages
It is considered the most efficient and cost effective type of earth rods.
It has high mechanical tensile strength and resistance to corrosion at lower cost as compared to other types of earth rods (solid copper or stainless Steel)
The high mechanical tensile strength of the steel bar enables the rod to be driven to great depths
The rod is usually treated to avoid oxidation of the copper bonding.
Galvanized Steel earth rods
In this type, the low carbon high tensile steel bar is hot dip galvanized with a coating of zink .
The zink coating will delay the corrosion of the steel bar by providing a sacrificial barrier.
Advantages
It is the cheapest of all earth rod types.
It has good corrosion resistance and conductivity.
The conductivity of zinc is 2.5 times the steel and more anti-corrosive and conductive
Disadvantages
It has the lowest resistance to corrosion
It has the lowest electrical conductivity and poor current carrying capacity.
Applications
The galvanized steel earth rods are suitable for use in non critical earthing systems in temporary structures such as antennas and electrical panels in construction sites .
Stainless steel earth rods
It is made of stainless steel bar
Advantages
It is used when extremely corrosion resistance and high mechanical strength is needed .
The stainless Steel earth rod is treated with an oxide layer that makes it more resistant to corrosion than copper.
It is used to overcome many of the problems caused by the galvanic corrosion that can take place between buried dissimilar metals being in close proximity to each other .
Stainless Steel earth rod provides high mechanical strength so it is unlikely to break or bend when driven into the ground even in rocky soil.
Disadvantages
It is the most expensive of all types of earth rods .
It has a lower electrical conductivity than other types of earth rods .
The current carrying capacity of steel earth rods is poor compared with copper earth rods
Application
It is primarily used in marine/shore environments and industrial processing .
Method of earthing by Rod electrodes
This method is the easiest and cheapest method of earthing as it does not require any excavation work.
It is suitable for sandy areas and it is used for temporary earthing purposeIn this method, an earth rod of 12.7 mm (1/2 inch) diameter or 16 mm (5/8 in) or 19 mm (3/4 in) diameter made of galvanized steel or solid copper or copper clad steel or stainless Steel is driven straight down into the ground manually to a depth not less than 2.44 m (8 ft) (as per nec code)
The rod is hammered manually or with the help of pneumatic hammer
The upper end of the rod should be kept below the ground level inside an earth pit the four sides of which have concrete or brick walls and is covered by cast iron plate.
The earth conductor is clamped to the top of the rod and run over to the building. 2 Plate electrodes
Plate electrodes are made of electrolytic solid copper sheet or steel sheet with electrolytic copper bonding
Plate electrodes are used in places where there are rocks fairly close to the ground surface which make it difficult to drive the earth rods to the required depths into soil
Plate electrodes are also used in places where there is high resistivity soil
Plate electrodes significally reduces the earth resistance in stony grounds as they increase the area of contact between the electrode and the ground.
Plate electrodes available in 600mm x 600m and 900mm x 900mm dimensions and 1.5mm or 3mm thick copper.
Method of earthing by plate electrodes
In this method, a plate electrode is used and is made from one of the following two materials :
1) a galvanized iron plate and its size should be not less than 60 cm × 60 cm × 6.35 mm (2 ft × 2 ft × 1/2 in) .
2) a copper plate and its size should be 60 cm × 60 cm × 3.18 mm (2 ft × 2 ft × 1/8 in) .
In the two cases the plate is buried vertically into the ground at a depth of not less than 3 m (10 ft) from the level of ground .
The plate is then surrounded by a small pieces of coke or charcoal and salt for a thickness of not less than 15 cm
A GI pipe of diameter 12.7 mm (1/2inch) is placed horizentally at a depth of 600 mm below the level of ground and then is bended to be in a vertical position till the top of the plate electrode and inside this pipe, an earth wire made of the same material as that of the plate electrode (copper earth wire for copper plate electrode and GI wire for GI plate electrode) is carried from the main earthing busbar till the top of the plate and is bolted tightly to the earthing plate with the help of bolts, nuts and washers .
Another GI pipe is placed at the top of the plate and a funnel is connected at the top of this pipe ,the top of the pipe with the funnel is placed inside an earth pit (the same as above) and a three or four buckets of water is poured into the funnel to keep the earth resistance at minimum value as possible.
3 Pipe electrodes
The pipe electrodes are usually made of galvanized iron and have holes pierced at regular intervals along the length and is narrow at the bottom end .
Method of earthing by pipe electrodes
The GI pipe is driven vertically and upright in a permanently wet soil and its size depends on the value of fault current to be carried and the type of soil.
The size of the pipe is usually 38.1 mm in diameter and 2 m in length for ordinary soils and the pipe length should be increased to 2.75 m in case of dry and rocky soils.
The depth at which the pipe should be buried depends upon the moisture condition of the soil.
The bottom of the pipe is surrounded by small pieces of coke or charcoal and salt for a minimum thickness of about 15 cm around the pipe and alternate layers of coke and salt are used till the top of the pipe as coke retains moisure and increases the effective area of the earth and salt decreases the earth resistance.
Another GI pipe which is 19.05 mm in diameter and 1.25 m in length (or longer) is then connected at the top of the GI pipe (the earth electrode) with the help of reducing socket .
A funnel is connected at the top of the 19.05 diameter pipe and the top of pipe with the funnel is placed inside an earth pit of size 30 cm × 30 cm × 30cm (1 ft × 1 ft × 1 ft) and the four sides of the pit have concrete or brick walls and is covered at the top with a cast iron plate .
During dry summer season, the earth resistance increases due to the decrease that happens to the moisure in the soil, so to increase conductivity and have an effective earth during summer , a suitable amount of water ( three or four buckets of water) is poured at regular periods into the funnel connected at the top of the 19 mm diameter pipe, which is further connected at the top of the GI pipe .
GI wire or a strip of GI earth wire is carried in a GI pipe (12 mm in diameter) at a depth of 60 cm below the ground level then this earth wire is fastened to the top of the GI pipe with the help of nuts and bolts .
The cross section area of the earth wire must be sufficient to carry the fault current safely .
4 Earth lattice
Earth lattice are manufactured from copper tape of various combination, these copper tapes are made of high conductive copper or electrolytic copper or electro tinned copper .
Earth lattice are often used for potential grading and are a preferred option on telecommunican towers and other applications to reduce the danger of high step and touch voltages that can cause problems to operators in situations such as high voltage switching.Earth lattice are used to provide a long-lasting, durable and high reliable earthing solution in high fault current applications as they provide a good earthing contact with a wide surface area of the surrounding soil.
Earth lattice are available in many sizes such as (500 × 500, 600 × 600, 900 × 900, 1000 × 1000) and thickness of 2 mm or 3 mm.Earth lattice provide high corrosion resistance, abrasion resistance and high electrical conductivity.
