802.3 is a standard specification for Ethernet, a method of packet-based physical communication in a local area network (LAN), which is maintained by the Institute of Electrical and Electronics Engineers (IEEE). In general, 802.3 specifies the physical media and the working characteristics of Ethernet.
IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The IEEE 802 standards are restricted to networks carrying variable-size packets, unlike cell relay networks, for example, where data is transmitted in short, uniformly sized units called cells.
Institute of Electrical and Electronics Engineers
IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The IEEE 802 standards are restricted to networks carrying variable-size packets, unlike cell relay networks, for example, where data is transmitted in short, uniformly sized units called cells.
Without IEEE 802 standards to build upon computer-to-computer connections, simple email, Internet access, World Wide Web, and mobile broadband would not have been possible to the extent we see today. IEEE 802 standards are undeniably an essential foundation of today's networked world.”
The Institute of Electrical and Electronics Engineers (IEEE) style is a widely accepted format for writing research papers, commonly used in technical fields, particularly in computer science.
An Example of an IEEE standard is IEEE 802.11 which refers to the rules/guidelines that define communication for wireless LANs. 3. Example of ITU-T standard are the new green ICT standards to improve the e-waste and energy efficiency.
The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms."
For measuring soil resistivity Earth Tester is used.It is also called the “MEGGER”.
- It has a voltage source, a meter to measure Resistance in ohms, switches to change instrument range, Wires to connect terminal to Earth Electrode and Spikes.
- It is measured by using Four Terminal Earth Tester Instrument.
There is not one standard ground resistance threshold that is recognized by all agencies. However, the NFPA and IEEE have recom- mended a ground resistance value of 5.0 ohms or less. The NEC has stated to “Make sure that system impedance to ground is less than 25 ohms specified in NEC 250.56.
The salt use as electrolyte to form conductivity between earth electrode (generally GI pipe or plate) Coal and Earth with humidity. Sand has used to form porosity to cycle water & humidity around the mixture. The layer of charcoal and salt helps to maintain low resistance for earth fault currents.
'Pipes may be of cast iron of not less than 100 mm diameter, 2.5 to 3 m long and 13 mm thick. Alternatively, 40 mm diameter G1 pipe in treated earth pit or 40 mm diameter MS rod can be directly driven in virgin soil. The earth rod shall be placed at 1.250 m below ground. '
So when there is a fault in the circuit the Earthing wire provide path for the current to flow to ground and the user will not get shock when touches the metal parts . So to drive sufficient current it should offer low resistance to drive more current to ground .
Earthing is an important component of electrical systems because of the following reasons: It keeps people safe by preventing electric shocks. It prevents damage to electrical appliances and devices by preventing excessive current from running through the circuit.
3 good ways to improve earth electrode resistance
- Lengthen the earth electrode in the earth.
- Use multiple rods.
- Treat the soil.
In grounding the current carrying part like neutral of the transformer is directly connected to the ground. The grounding wire is placed between the neutral of the equipment and the earth whereas in earthing the earth electrode is placed between the equipment body and the earth pit which is placed under the ground.
Earthing Grid, is an arrangement in a plant which is very important for a few reasons, all of which are related to either the protection of people and equipment and/or the optimal operation of the electrical system.
Earth is used as an electrical conductor for electricity by man over 270 years back. The other name for Electrical Earthing is Grounding. Electrical earthing is done to protect ourselves from shock during fault conditions. The common electrode used for Earthing is copper, which is used for grounding.
To achieve this:
- An area of 1.5m X 1.5m is excavated to a depth of 3m.
- The pit is half filled with a mixture of wood coal powder, sand and salt.
- A 500mm X 500mm X10mm GI plate (earth plate) is placed in the middle.
- Connections between the earth plate and the surface are installed for system earthing.
2. Main Earthing Terminal or Bar. Main earthing bar is to be provided at point of service entrance or main distribution room, and as described in the Specification or shown on the Drawings. Connect all earthing conductors, protective conductors and bonding conductors to the main earthing bar.
GI wire is the most common material for wire from building mains to earth. Earthing is done by a copper plate burried deep underground at a level where it remains in contact with ground water beneath.
The world's highest sustained man-made voltage was 32 (+/- 1) million volts. This was generated at Oak Ridge National Laboratory (Oak Ridge, TN, USA) using a special-purpose tandem electrostatic generator called a Pelletron, manufactured by National Electrostatics Corp.
According to the rules and regulations any voltage below 50V AC and 120 V DC are relatively safe.
The real Earth (the planet you are probably standing on) is electrically neutral. This means that it has the same number of electrons and protons, so their charges cancel out overall. Scientifically, we describe this by saying that the Earth has an Electric Potential of zero.
"Touch voltage" is the voltage between the energized object and the feet of a person in contact with the object. The touch voltage could be nearly the full voltage across the grounded object if that object is grounded at a point remote from the place where the person is in contact with it.
An ESI site is classed as 'hot' if the rise of earth potential under fault conditions exceeds 430V for normal reliability power lines or 650V for high reliability lines.
a. Reduce the potential voltage source to an acceptable level. This includes correcting bad neutral connections and removing faulty loads; improving or correcting wiring and grounding; balancing load or controlling leakage current by cleaning, re-insulating or grounding.
A battery that is powering a circuit is a potential rise, meaning the potential difference across the battery is a positive number. If there's only one battery, it must be the power source, so it must be a potential rise.
STEP AND TOUCH VOLTAGES The step and touch voltages test is performed applying current between the ground grid and the auxiliary ground spikes, and measuring the step or touch voltage with the test probes. With the STLG option, the current generation is performed using an overhead line to connect to the remote ground.
