Which of the following is the least expensive protection for overcurrent is a low voltage system?

Which of the following is the least expensive protection for overcurrent is a low voltage system?

Right Answer is:

Rewireable fuse


A fuse is a device, which protects the electrical wires, cables, and other electrical equipment against overloading and short circuit. It contains a fuse element, generally thin wire or strips mounted on an insulated base. It is heated and destroyed while passing an excessive current through it. It breaks the circuit by melting the fuse element when the current flowing in the circuit exceeds a certain predetermined value. The fuse is placed in series with the equipment or its parts which are to be protected.

Types of Fuses

They are of the following two types:

  1. Rewirable fuse.
  2. Totally enclosed or cartridge fuse.

Rewirable fuse

In the case of a rewirable fuse, the blown-out fuse element can be replaced by a new element. The fuse element can be either open or semi-enclosed. An open type is rarely used. Semi-enclosed type is generally used for low-voltage applications in houses and installations for up to 440 V. This is the cheapest and simplest form of protection.

A rewirable fuse is a set of two units. One is known as the base unit and the other is known as the fuse carrier. Fuse elements can be fixed, removed, and refixed in the fuse carrier. Fuse-carrier is also known as removable Unit. The base unit is the permanently fixed unit with the switchboard.

Both the units are fixed on the porcelain chassis. The incoming wire is connected with the metal clip on one side of the porcelain base. The outgoing wire is connected with the other terminal of the porcelain base. These two terminals situated inside the base of the fuse carrier are interconnected by fuse wire. This fuse wire is the weakest part of the circuit which melts during overloading or short circuit. After that, a new fuse wire is connected between the terminals. A constructional diagram of the rewirable fuse is shown in Figure.

Advantages of rewireable fuses:

  1. Cheap and simple to install.
  2. Due to a rewireable feature, it can be used for a long period of time until the contacts are in good condition.
  3.  Low maintenance is required.

Disadvantages of rewireable fuse:

  1. The exact estimation of wire diameter is a challenge at times.
  2. Less reliable operation, as it is affected by ambient temperature.
  3. Due to low-current breaking capacity, it cannot be employed with the circuits having the probability of large currents.
  4. Continuous heating of the fuse element results in oxidation, which causes the fuse to blow at a current below its rated current.
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