The term grounding, in electrical terminology, means connected either directly or indirectly to earth. The purpose of grounding is for safety. Grounding can be divided into two section; system grounding, which is grounding of current-carrying portion of the system and equipment grounding, which is grounding of equipment not intended to be at a voltage potential difference from the earth. These two types of grounding have distinctly different functions as will be discussed in the following two section.
The principle reason for system grounding is to limit the voltage between any conductor and the earth to a minimum value for the system being used. Before going on, let us more carefully define the term voltage to ground. A ground can be a grounding electrode or any conductive material connected directly or indirectly to earth. For example, metal pipes (water, gas,drain) in a building are connected to other pipes, which in turn are buried in the ground. Thus metal pipes can be considered as paths to ground or grounds. Voltage to ground will be the voltage between any point in the electrical system and any object that is grounded.Good system grounding is dependent on establishing low resistance paths to earth at each system grounding point. The grounding electrode system is made up of components which contact the earth. The NEC(250-81) states that if available on the premises, at each building or structure each of the following items should be bonded together to form the grounding electrode system: (a) metal underground water pipe with at least 3 m in the earth (b) metal frame of the building where effectively grounded (c)concrete-encased electrode- and electrode encased in at least 51 mm of concrete, located within or near the bottom of a concretere foundation (d) ground ring encircling the building at least 76 cm below the surface..(source:Fundamentals of electricity for agriculture by Robert J. Gutason)
The principle reason for system grounding is to limit the voltage between any conductor and the earth to a minimum value for the system being used. Before going on, let us more carefully define the term voltage to ground. A ground can be a grounding electrode or any conductive material connected directly or indirectly to earth. For example, metal pipes (water, gas,drain) in a building are connected to other pipes, which in turn are buried in the ground. Thus metal pipes can be considered as paths to ground or grounds. Voltage to ground will be the voltage between any point in the electrical system and any object that is grounded.Good system grounding is dependent on establishing low resistance paths to earth at each system grounding point. The grounding electrode system is made up of components which contact the earth. The NEC(250-81) states that if available on the premises, at each building or structure each of the following items should be bonded together to form the grounding electrode system: (a) metal underground water pipe with at least 3 m in the earth (b) metal frame of the building where effectively grounded (c)concrete-encased electrode- and electrode encased in at least 51 mm of concrete, located within or near the bottom of a concretere foundation (d) ground ring encircling the building at least 76 cm below the surface..(source:Fundamentals of electricity for agriculture by Robert J. Gutason)
Find Exclusive Tutorial From:
0 komentar:
Post a Comment