# Fuses

### What is a FUSE?

Fuse is a basic device used to break the circuit when there is a overcurrent.it consists of metal wire fuse element which is connected by two terminal.fuse element will be blow if the current through it exceeds the limit was set.

Its use is widespread due to the efficiency and durability.Also, if the price is cheap compared with other protective device.we can find a variety of fuse which is used widely different in appearance and appropriate use of an electrical circuit.

### Types of FUSE

According to British standard code ( BS )

1. BS 88      = HRC ( High Rupture Capacity )
2. BS 1361 = Cartridge Fuse
3. BS 3871 = MCB ( miniature circuit breaker )
4. Bs 3036 = Rewire Fuse

### Characteristic

a) Speed of blow

Speed to blow the metal element in fuse depends on the type of fuse is made.There are several types of fast blow, slow blow or interval of time blow depends on the use.

b) Breaking Capacity

The breaking capacity is the resistance to sustain a safe amount of current through the fuse.normally set it at 10 times ( 10 x ) the current value in the fuse.

c) Rated voltage

Voltage rating of the fuse must be greater than or equal voltage source.This requirement applies to every type of fuse.It is for safety purpose.if not the fuse may be explode or broken if voltage greater than specs. (200 VAC until 600VAC)

d) Temperature

Ambient temperature will effected to efficiency of fuse . A fuse rated for 1 ampere at temperature 25°C may  increase  the breaking capacity to 10% or 20% higher.For more detail please refer manufacture guideline.

e) Voltage drop

A voltage drop of fuse is usually provided by  manufacturer.Fuse resistance will be quickly heated when the current through voltage drop should be taken into account when selecting an appropriate fuse

f) Material

There are various types of materials used to make fuse.It depending on the size, type and normally use it. usually it made from ceramic,glass,fiberglass and plastic.

### HOW TO CALCULATE FUSE SIZE?

Use this formula for calculate fuse size for electrical circuit

In = 0.725 x Iz

In = Fuse ampere

Example :

We want install 1 unit exhaust fan.the full load ampere is 18 Ampere.Calculate fuse rating for this circuit.

In = 0.725 x Iz

In = 0.725 x 18 ampere

In = 13 ampere ( we use 16 ampere HRC fuse )

Fuse BS 88 ( HRC ) code application

1) gG = General application

2) gM = Motor protection ( full range )

3) aM = Motor protection circuit ( partial voltage )

Standard size for Fuse BS 88 ( HRC )

5A,6A,10A,16A,20A,25A,32A,40A

63A,80A,100A,125A,160A,200A