guiadeayuntamientos.info: Electricity & Magnetism: Magnetic Fields
magnetism, and the relationship between the two, are fundamental to the This unit also addresses topics such as: Earth's magnetic field, electrical safety. Electricity is a form of electrical energy that is transmitted through the wires for operating the various machines and devices. Without taking account of the relation between bio-electrical processes in the human body and electromagnetic processes in the earth, in other words body.
If any exposed metal part should become energized faultsuch as by a frayed or damaged conductor, it creates a short circuit, causing the overprotection device circuit breaker or fuse to open, clearing disconnecting the fault.
It is important to note this action occurs regardless of whether there is a connection to the physical ground earth ; the earth itself has no role in this fault-clearing process  since current must return to its source; however, the sources are very frequently connected to the physical ground earth.
By bonding interconnecting all exposed non-current carrying metal objects together and to other metallic objects such as pipes or structural steel, they should remain near the same voltage potential, thus reducing the chance of a shock. This is especially important in bathrooms where one may be in contact with several different metallic systems such as supply and drain pipes and appliance frames.
When a system needs to be connected to the physical ground earththe equipment bonding conductor also becomes the equipment earthing conductor see above.
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Metal water pipe used as grounding electrode A grounding electrode conductor GEC is used to connect the system grounded "neutral" conductor, or the equipment to a grounding electrode, or a point on the grounding electrode system.
This is called "system grounding" and most electrical systems are required to be grounded.
In the past, water supply pipes were used as grounding electrodes, but due to the increased use of plastic pipes, which are poor conductors, the use of an actual grounding electrode is required. This type of ground applies to radio antennas and to lightning protection systems. Permanently installed electrical equipment, unless not required to, has permanently connected grounding conductors. Portable electrical devices with metal cases may have them connected to earth ground by a pin on the attachment plug see Domestic AC power plugs and sockets.
The size of power grounding conductors is usually regulated by local or national wiring regulations. Earthing system In electricity supply systems, an earthing grounding system defines the electrical potential of the conductors relative to that of the Earth's conductive surface.
The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. Regulations for earthing systems vary considerably between different countries. A functional earth connection serves more than protecting against electrical shock, as such a connection may carry current during the normal operation of a device.
Such devices include surge suppression, electromagnetic-compatibility filters, some types of antennas, and various measurement instruments. Generally the protective earth system is also used as a functional earth, though this requires care.
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Impedance grounding[ edit ] Distribution power systems may be solidly grounded, with one circuit conductor directly connected to an earth grounding electrode system. Alternatively, some amount of electrical impedance may be connected between the distribution system and ground, to limit the current that can flow to earth.
The impedance may be a resistor, or an inductor coil. In a high-impedance grounded system, the fault current is limited to a few amperes exact values depend on the voltage class of the system ; a low-impedance grounded system will permit several hundred amperes to flow on a fault.
A large solidly grounded distribution system may have thousands of amperes of ground fault current. In a polyphase AC system, an artificial neutral grounding system may be used.
Although no phase conductor is directly connected to ground, a specially constructed transformer a "zig zag" transformer blocks the power frequency current from flowing to earth, but allows any leakage or transient current to flow to ground. Low resistance grounding systems will have a time rating say, 10 seconds that indicates how long the resistor can carry the fault current before overheating.
A ground fault protection relay must trip the breaker to protect the circuit before overheating of the resistor occurs. They have a continuous rating, and are designed to operate with a single-ground fault.
This means that the system will not immediately trip on the first ground fault. If a second ground fault occurs, a ground fault protection relay must trip the breaker to protect the circuit. On an HRG system, a sensing resistor is used to continuously monitor system continuity.
If an open-circuit is detected e. Without a sensing resistor, the system could continue to operate without ground protection since an open circuit condition would mask the ground fault and transient overvoltages could occur. Examples of such installations include patient care areas in hospitals, where medical equipment is directly connected to a patient and must not permit any power-line current to pass into the patient's body.
All magnetic objects have field lines and poles.
It can be as small as an atom or as large as a star. Attracted and Repulsed You know about charged particles. There are positive and negative charges. You also know that positive charges are attracted to negative charges.
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- Magnetic Field Basics
A French scientist named Andre-Marie Ampere studied the relationship between electricity and magnetism. He discovered that magnetic fields are produced by moving charges current.
And moving charges are affected by magnets. Stationary charges, on the other hand, do not produce magnetic fields, and are not affected by magnets. Two wires, with current flowing, when placed next to each other, may attract or repel like two magnets. It all has to do with moving charges. Earth's Magnetic Field Magnets are simple examples of natural magnetic fields.
The Earth has a huge magnetic field. Because the core of our planet is filled with molten iron Fethere is a large field that protects the Earth from space radiation and particles such as the solar wind. When you look at tiny magnets, they are working in a similar way.How To Install Electrical Earthing at Home ( In Hindi )
The magnet has a field around it. As noted earlier, current in wires produces a magnetic effect. You can increase the strength of that magnetic field by increasing the current through the wire.