(1) A switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. while a fuse (from the French fuser, Italian fuso, "spindle"[1]) is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit.
A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing. The fuse is arranged in series to carry all the current passing through the protected circuit. The resistance of the element generates heat due to the current flow. The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit.
The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt quickly on a small excess. The element must not be damaged by minor harmless surges of current, and must not oxidize or change its behavior after possibly years of service.The fuse element may be surrounded by air, or by materials intended to speed the quenching of the arc. Silica sand or non-conducting liquids may be used.
n the simplest case, a switch has two conductive pieces, often metal, called contacts, connected to an external circuit, that touch to complete (make) the circuit, and separate to open (break) the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working. Contact materials are also chosen on the basis of electrical conductivity, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity.[3]
Sometimes the contacts are plated with noble metals. They may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as conductive plastic, are sometimes used. To prevent the formation of insulating oxides, a minimum wetting current may be specified for a given switch design.
The function of switch remains same as it makes or breaks current in a circuit.When switch connects circuit path it has a resistance of mΩ, when current path is broken, then resistance is high MΩ and higher. This resistance and maximum voltage that can be applied to insulation is often major important and vital feature that leads to switch stability.
The function of switch remains same as it makes or breaks current in a circuit.When switch connects circuit path it has a resistance of mΩ, when current path is broken, then resistance is high MΩ and higher. This resistance and maximum voltage that can be applied to insulation is often major important and vital feature that leads to switch stability.
We all know that when current flows through the conductor, because there is a certain resistance of the conductor, so the conductor will heat. And heat followed this formula: Q = 0.24I2RT; where Q is the heat, 0.24 is a constant, I is the current flowing through the conductor, R is the resistance of the conductor, T is the current flowing through the conductor of the time; so the formula we can see the working principle of a simple fuse was.
When the production of materials and shapes to determine the fuse, and its relative resistance to determine R (without considering its temperature coefficient of resistance). When the current flows through it, it will be hot, with time to increase its heat is also increasing. The size of current and resistance determine the rate of heat fuse the situation of the construction of its installation to determine the rate of heat dissipation, if the rate of heat dissipation is less than the rate of heat when the fuse is not blown. If the rate of heat equal to the rate of heat dissipation when a long period of time it will not fuse. If the heat is greater than the speed of the speed of heat dissipation, then heat will be more and more. And because it has some heat and the quality of the performance of the heat gain to the increase in temperature, when the temperature rises to above the melting point of the fuse on the fuse had blown. This is how the fuse works..
(5) In an electrical context, 'tripping off' means the circuit breaker breaking the circuit because of a fault. When a loose connection (a gap) is made in the faulted circuit so loose that the current flowis non-continuous, it is called an arcing or arc fault.
phenomenon ::: When an overcurrent is interrupted by the circuit breaker by opening its contacts, current tries to bridge the gap. In an attempt to maintain the circuit, the air heats up and becomes a conductor. As a result an arc forms. In general, when air and gases are heated, they become electric conductors. The hotter they get, the better they conduct. that is called arc. !
((or)) When a loose connection (a gap) is made in the faulted circuit so loose that the current flowis non-continuous, it is called an arcing or arc fault. An electric arc is an electrical breakdown ofa gas which produces an ongoing plasma discharge, resulting from a current flowing throughnormally nonconductive media such as air. The arc consists of a column of ionized gas havingmolecules which have lost one more electrons. The electrons being negatively charged areattracted towards the positive contact with high velocity and on the way they detach moreelectrons by impact. The positive ions are attracted towards the negative contact but theycomprise almost the entire weight of the atom, they move relatively slow.
The heat from an uncontrolled arc in a circuit breaker can cause a rapid and violent expansion of the nearby air and could severely damage the circuit breaker. Therefore, besides separating the electrical contacts, a circuit breaker also has to quickly extinguish the arc. A number of factors can be employed for quenching the arc, such as, speed, distance, dielectric strength, cooling etc.
a) Speed : When the contacts separate rapidly, there is less time for the arc to form and maintain itself.
b) Distance : When the distance between opened contacts is more, the arc has to stretch more to maintain the current flow which requires more voltage.
c) Cooling : When the arc is forced against a cold material, it absorbs and dissipates the heat.
d) Dielectric Strength : When the arc is submerged in a medium with higher dielectric strength than air (sulfur hexafluoride, SF6), the insulating nature of the medium helps in quenching the arc.
In an MCB, arc chutes or arc dividers are used for arc quenching. When the contacts of an MCB separate, generating an electrical arc between them through air, the arc is moved into the arch chute where it is divided into small segments. The overall energy level of the arc gets split up which is not sufficient to sustain the arc and therefore it gets dissipated.
