Questions

1. What is short circuit? What is the common cause of unintentional short circuits in electrical devices?
2. What is a fuse? What happens when you blow a fuse?
3. How do Circuit breakers Work?
4. When is there an overload in a circuit?
5. Why will too many electrical devices operating at one time often blow a fuse?
6. What are the dangers of short circuit and overload?


Answers:

1. A short circuit is an abnormal condition (including an arc) of relatively low impedance, whether made accidentally or intentionally, between two points of different potential in an electric network or system.Common usage of the term implies an undesirable condition arising from failure of electrical insulation, from natural causes (lightning, wind, and so forth), or from human causes (accidents, intrusion, and so forth). From an analytical viewpoint, however, short circuits represent a severe condition that the circuit designer must consider in designing an electric system that must withstand all possible operating conditions.

2. A fuse is an expendable protective device that eliminates overload on an electric circuit. The fuse is connected in series with the circuit being protected. The components of a typical low-voltage high-power fuse are a fuse element or wire, an insulating material support and housing, two metal end fittings, and a filler.When you blow a fuse, the wire usually snaps in two, and the power running through that circuit is immediately cut off. The excess heat buildup occurs whenever appliances draw more amperage than the circuit can handle.

3. A circuit breaker is a device to open or close an electric power circuit either during normal power system operation or during abnormal conditions. A circuit breaker serves in the course of normal system operation to energize or deenergize loads. During abnormal conditions, when excessive current develops, a circuit breaker opens to protect equipment and surroundings from possible damage due to excess current. These abnormal currents are usually the result of short circuits created by lightning, accidents, deterioration of equipment, or sustained overloads.

4. An electrical overload is a situation where the wiring to or within a machine or system is subjected to a greater electric current load than it was designed to carry, leading to excessive heating of the wires and a possibility of fire. This excessive current load can be a result of electrical insulation failure (a short circuit) or human error.In an electrical overload, it leads to excessive heating of the wires and a possibility of fire.

5. In an electrical overload, it leads to excessive heating of the wires and a possibility of fire.
In a short circuit, an accidental low-resistance connection between two nodes of an electrical circuit that are meant to be at different voltages. This results in an excessive electric current limited only by the Thevenin equivalent resistance of the rest of the network and potentially causes circuit damage, overheating, fire or explosion. Although usually the result of a fault, there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing crowbar circuit protectors.

6. A short circuit-occurs when conductors of opposite polarity are accidentally bridged by a conductive object or bridged to grounded metal. Metal screwdrivers, wrenches, fish tapes, test instruments, etc. have all been found to have made inadvertent contact while persons were working on live equipment. An arcing fault may be established that is limited only by the total impedance of the circuit. The arcing will continue until circuit breaker, fuse, or equipment ground fault protection device on the line side of the fault opens the circuit. Even if the short circuit protective device opens the circuit without any intentional delay, portions of the conductors and other metallic materials in the path of the arc may explode violently, showering the area with hot molten metal that can cause severe burns or death. The flash associated with the arc can also cause permanent eye damage. Finally, a short circuit may expel shrapnel toward the workman, penetrating clothing or the body.
Overload-leading to excessive heating of the wires and a possibility of fire. This excessive current load can be a result of electrical insulation failure ( a short circuit) or human error.

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