BEEME – Fuse

Fuse

Fuse is a device used in a circuit for protecting electrical equipment against overloads and short circuits. The fuse is connected in series with the equipment to be protected. The fuse element or fuse wire is that part of the fuse which melts when an excessive current flows through it and isolates the device from the supply circuit. When the current through the fuse is above the normal value either due to faulty equipment or due to high supply voltage the fuse blows off, isolating the equipment from the supply.

Advantages

  1. It interrupts large currents without noise, flame, gas or smoke
  2. Easy maintenance
  3. Fault detection and protection of equipment
  4. Unlike circuit breakers, no separate circuit is required for operation

Disadvantages

  1. Needs to be replaced or rewired after it blows
  2. Since its used in series, selectivity of equipment is not possible.

Desirable properties of fuse element

  1. Low melting point for quick operation
  2. High conductivity
  3. Low cost
  4. Low ohmic losses
  5. Free from deterioration due to oxidation
    1. Commonly used elements are lead, tin, copper, zinc and silver.
    2. For low currents tin or alloy of tin and lead can be used.

Types of fuses

  • Semi-enclosed or rewireable or kit-kat fuse.
    1. Commonly used in all households. Simple construction. Cheap.
    2. The fuse carrier holds the fuse element between its terminals
    3. The fuse carrier can be inserted or taken out of the base when desired.

  • Cartridge fuse
    1. Fuse element is placed in a totally enclosed fuse carrier with two metal contacts on either side of the carrier.
    2. Entire cartridge has to be replaced after the fuse blows.

  • High rupturing capacity (HRC) fuse
    1. Consists of a heat resisting ceramic body having metal (brass) end caps.
    2. Space within the body is packed with quartz powder, which acts as an arc extinguishing agent.

  • Liquid fuse
    1. Fuse element is surrounded by an arc extinguishing liquid usually hydrocarbon.
    2. Fuse element is normally of silver strip or wire and is housed in a body consisting of a glass tube with metal ferrules at each end.
  • Expulsion fuse
    1. Fuse consists of a tube of insulating material into which the fuse element is inserted.
    2. When the element melts and arcing takes place, the resultant gas pressure causes the arc to be blown out of the ends of the tube and thus is extinguished.
      1. Disadvantage – for large fault currents the arc expulsion is violent.