The fuses are of the following types:
(a) Open type fuse,
(b) Semi-enclosed type, and
(c) Totally enclosed type.
Out of these three types generally for house wiring and general purpose the semi-enclosed type fuse are used.
Semi-enclosed type fuse. In this type of fuse the fuse element is neither Open nor totally enclosed. Such types of fuses are used for house wiring purpose, for example fuse cutout and kit ket fuse.
(i) Fuse cut out. These are made of porcelain. It has two main parts known as the base and cover. The base has two terminals Or plates. The fuse wire is connected between these two plates or terminals, through a porcelain channel as shown in Fig. 4.1 . A cover is also provided to cover it from the external disturbances and also to avoid the sparking etc. not to come out.
Fig. 4.1. Fuse cut-out.
(ii) Kit kat fuse. It is a common type of fuse generally used in house wiring system.
There are two main parts, the base and carrier.
- Fuse base. It is made of porcelain and is a fixed part of the kit kat fuse. It has two terminals and one or two holes for fixing with the wall or board etc. with the screws as shown in Fig. 4.2. One terminal is connected with live wire and other to the load or wire connecting load. Sometimes, to avoid the earth fault, an asbestos sheet is provided over the fixing screw.
Fig. 4.2. Fuse base and carrier.
- Fuse Carrier. It is an removable part of the fuse. It is also having two terminals generally with strips having some spring tensions, where the fusing element is connected. Sometimes the fusing element is put in a hole so that if the fuse melts, it may not cause any danger to the surroundings thus it is safe. If the fuse is used for service-mains then the metallic shielding is provided and earthed. It is also sealed by the supply company. This type Of fuse are having some advantages.
Advantages:
(i) If fuse melts. the spark does not come out.
(ii) Replacement is easy.
(iii) All size of fuse wires can be used in this type of fuses up to some extent.
Availability. These are available according to the voltage and Current capacity. According to the voltage these are 250 V and 500 V. According to current capacity these are 15 A, 30 A, 60 A, 100 A, etc.
What is open type fuse?
The fuse which is used in open space is called open type of fuse as shown in Fig. 4.3. In this type of fuses the fusing element is kept open in the atmosphere. Generally this type of fuses are used with the overhead lines, on poles for giving the supply to the consumers. These are connected in series with the load.
Fig. 4.3. Open type fuse.
As shown in the figure, it has two terminals mounted over the insulated sheet and the fusing element is kept free and open to the atmosphere.
This type of fuses have the following disadvantages:
(i) The replacement is not easy, because one terminal is always live.
(ii) The fusing current is not constant, as it also depends upon the environmental changes.
(iii) In case of fusing, the molten metal or spark may fall on such articles which may catch fire. So there is a possibility of fire also.