Salt and charcoal increase the conductivity of the soil in the earth pit. As a result, the fault current finds it easy path through equipment to the earth. The alternate layers of charcoal and salt maintain low resistance for earth fault currents.
Adding charcoal, salt, and watering in earthing pit decreases soil resistivity.
We use conventional pipe and plate earthing for earthing purposes. Two types of material are used in the earth pit to fill the earth pit.
Before understanding the concept behind the use of salt and charcoal for earth pit, let’s first understand the properties of these materials.
Earthing Pit Materials
The wood, other plants, and animal materials are volatile materials and these can be burned. On strongly heating up these materials, we can easily remove all water and volatile constituents. After removing water & volatile contents, the black carbon residuals are left is known as charcoal.
The properties of charcoal are,
- It is porous material
- Absorbs moisture from air- Hygroscpic
- charcoal is an allotrope of carbon and acts as a conductor of electricity
It is an ionic compound. It has a strong attraction for polar water molecules. Thus, the salt absorbs moisture from the soil and keeps the earth pit moist.
The charcoal and salt perfectly make the ionic bonding with moisture in the soil. Thus, the water content in the earth pit increases. The moisture increases the conductivity of the earth pit.
The earth resistance of the earthing pit is the combined resistance of the earth pit and the surrounding soil. The soil conductivity differs with types of soil. Therefore, it is a must to check the conductivity of the soil before making an earth pit.
Why are salt and charcoal used in earth pit?
- The charcoal and soil both absorbs the moisture from the soil. The salt can make a good bonding with charcoal,soil and water. Thus, the both materials used the earth pit increase the conductivity of the earth pit.
- The charcoal and coal can retain the absorbed moisture for a longer period of time.
- Salt and charcoal minimize the earth pit resistance. Thus, it provides the least resistance path to the fault current.
- The low value earth resistance leads to easier passing of the fault current to ground. Thus, it provides protection to machines and humans.
Maintenance of Earthing Pit
We must take the following steps to ensure the healthiness of the earth pit.
- Measure the earth pit resistance on the most dry day once in a year.
- Record the resistance
- If resistance is high take necessary action to lower the resistance by watering the pit.
- Again measure the resistance
- If resistance OK, no action required
- If resistance not OK, discard the earth pit
- Salt and Charcoal have leaching properties. It means these materials washed away after some time. Therefore, periodical checking and maintenance is must for its healthiness.
The high resistance of the earth pit may cause serious accidents because the step voltage and touch potential increase with an increase of the earth resistance. Therefore, it is of utmost importance to keep the earth pit resistance as lower as possible.
We can perform the soil treatment to lower the resistance as per IEEE80-2013 standard.
What is the ratio of salt & Charcoal in Earthing?
A ratio of 3:1 of charcoal and salt is good for earthing pit.