Lightning, line surges or unintentional contact with higher voltage
lines can cause dangerously high voltages to the electrical distribution system
wires. Grounding provides an alternative path around the electrical system of your
home or workplace which minimizes damage from such occurrences.
Voltage stabilization:
There are many sources of electricity. Every transformer can be considered a
separate source. If there were not a common reference point for all these voltage sources
it would be extremely difficult to calculate their relationships to each other. The earth
is the most omnipresent conductive surface, and so it was adopted in the very beginnings
of electrical distribution systems as a nearly universal standard for all electric systems.
Current path in order to facilitate the operation of over-current devices:
This purpose of grounding is the most important one to understand. A grounding
system provides a certain level of safety to humans and property in case
of equipment damages.
Definition: NEC Article 100 and Section 250-70 define bonding as the permanent
joining of metallic parts to form an electrically conductive path which will assure
electrical continuity and the capacity to conduct safely any current that is likely
to be imposed.
The need for proper grounding is universally recognized to provide:
1. Safety from electric shock.
2. Protection of equipment or apparatus from damage by electrical faults.
3. Better reliability and continuity of electric service.
4. Methods of circuit relaying to clear ground faults on the electrical system.
Because of the great importance of the ground system whenever it is required
to function, it is essential to plan any grounding system completely and carefully.
The first consideration in any ground is the soil itself.
The materials comprising of the earth’s surface have a very high resistivity
compared with the low resistance of metals. As a result, all current flowing
through the ground has a considerable voltage drop in a short distance. It is
apparent from this, that the conception of the ground potential as always being
zero is not true. A considerable potential gradient is quite possible between
different portions of the ground, more particularly between those portions which
are immediately adjacent to a ground electrode and those portions which are remote
from the ground electrode. There is considerable variation in the resistance of the soil
itself. The resistance depends upon many factors, such as:
1. Type of soil
2. Depth
3. Temperature
4. Moisture content
5. Percent of salt concentration in the soil
