Earthing or Grounding of electrical installation is a common practice. However, some common terms used in the practice could sometimes be tricky. Here, we have attempted to provide explanations for some of the more common terms used when earthing or grounding an installation. These terms are the ones used in the various national and international standards:
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| Earthing an Electrical Installation |
Earth electrode
This is the conductor or group of conductors in intimate contact with, and providing an electrical connection with Earth.
Earth
This is the conductive mass of the Earth, whose electric potential at any point is
conventionally taken as zero.
Electrically independent earth electrodes
These are earth electrodes located at such a distance from one another that the maximum current likely to flow through one of them does not significantly affect the potential of the others.
Earth Electrode Resistance
This is the contact resistance of an earth electrode with the Earth.
Earthing Conductor
This is a protective conductor connecting the main earthing terminal of an installation to an earth electrode or to other means of earthing.
Exposed-conductive-part
This is the conductive part of equipment which can be touched and which is not a live part, but which may become live under fault conditions. Usually all exposed conductive parts are connected to the earth electrode by protective conductors with the object of providing a low resistance path for fault currents flowing to earth.
Protective conductor
This is the conductor used for some measures of protection against electric shock and intended for connecting together any of the following parts:
(a) Exposed-conductive-parts
(b) Extraneous-conductive-parts
(c) The main earthing terminal
(d) Earth electrode(s)
(e) The earthed point of the source or an artificial neutral
Extraneous-conductive-part
This is a conductive part liable to introduce a potential, generally earth potential, which is not part of the electrical installation. Examples of extraneous conductive parts include:
(a) Non-insulated floors or walls, metal framework of buildings
(b) Metal conduits and pipework (not part of the electrical installation) for water, gas, heating, compressed-air, etc. and metal materials associated with them.
Bonding conductor
This is the protective conductor providing equipotential bonding.
Main Earthing Terminal
This is the terminal or bar provided for the connection of protective conductors, including equipotential bonding conductors, and conductors for functional earthing, if any, to the means of earthing.
Equipotential bonding
Equipotential bonding simply means terminating all the extraneous conductive parts to the earthing system of the installation in a process referred to as bonding.
Bonding is carried out by protective conductors and the aim is to ensure that,
in the event of an incoming extraneous conductor (such as a gas pipe, water pipe etc.) being raised to some potential due to a fault external to the building, no difference of potential can occur between extraneous-conductive-parts within the installation.