Question

How short -circuit occurs in an electric fuse?​

Answer 1

Explanation:

A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages. This results in an electric current limited only by the Thévenin equivalent resistance of the rest of the network which can cause 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.

In circuit analysis, a short circuit is defined as a connection between two nodes that forces them to be at the same voltage. In an 'ideal' short circuit, this means there is no resistance and thus no voltage drop across the connection. In real circuits, the result is a connection with almost no resistance. In such a case, the current is limited only by the resistance of the rest of the circuit.

or

when live wire toches neutral wire then short circuit happens

Answer 2

Shot-circuit in the fuse wire occurs by the heat of current melting the wire to break the circuit.

Explanation:

In electricity Shot circuit is a term used generally for an ideal condition of connected path for the flow of current which offers no impedance or very less impedance.

In case of an electric fuse this term has different meaning which is somewhat analogous to the above meaning of the term shot-circuit.

• It is a condition of blown away or melted fuse wire that is connected in series with the load so that there is absence of path for the flow of current and the circuit is open now. (i.e we can imagine to complete the circuit by jumping of the current from the two disconnected point such that there is no resistance for serving our purpose of operating the connected load).

As we know that resistance of a wire is given as:

$R=\rho.\frac{l}{a}$

where:

$\rho=$ specific resistance of the wire material

l = length of the wire

a = cross section area of wire

• When the current in the circuit increases then according to the Joule's law the heat produced also increases which in turns melts the wire and breaks the circuit as a safety measure to prevent the load from any damage.

Mathematically, Joule's Law is given as:

$Q=I^2.R.t$

where:

Q = heat produced

I = current in the circuit

R = resistance of the circuit

t = time for which the current flows

This heat gets dissipated into the surrounding until it is within the limits but when an excess of heat is produced then it melts the fuse wire.

• This is the reason why fuse wires are usually made thin so that they offer more resistance and produce more heat which melts the thin wire easily and the material should also have a low fusion (melting) point for the safety reason.

TOPIC: joule's law, resistivity, resistance

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