Important Terms regarding Electric Fuse.

For doing analysis of fuses we must have idea regarding the following terms.

Table of Contents.

1. What is the current rating of a fuse?

2. What is the fusing current?

3. What is the fusing factor?

4. What is prospective current?

5. What is cut-off current of a fuse?

6. What is pre-arcing time of a fuse?

7. What is arcing time of a fuse?

8. What is total operating time of a fuse?

9. What is the breaking capacity of a fuse? 

Current rating of a fuse element.

What is the current rating of a fuse?

• It is the current which the fuse element can normally carry without overheating or melting. It depends upon the temperature rise of the contacts of the fuse holder, fuse materials and the surroundings area of  the fuse.

What is the fusing current?

Fusing current.

• It is the minimum current at which the fuse element starts melting and disconnects the circuit protected by it. This value must be more than the current rating of the fuse element.

The fusing current depends upon the various factors.

1. Materials of the fuse element.
2. Length of fuse.
3. Fuse diameter.
4. Size and location of fuse terminals.
5. Type of enclosure used.
6. Previous history of fuse.

Read more: What is the working principle of fuse?

What is the fusing factor?

• It is the ratio of minimum fusing current to the current rating of the fuse element. Its value is always more than one.
• It the fusing factor is small then the difficulty is more in avoiding the deterioration due to overheating and oxidation at rated carrying current.

What is Prospective current?

• It is the r.m.s. value of the first loop of the fault current obtained if the fuse is replaced by an ordinary conductor of negligible resistance.

What is Cut-off current of a fuse?

• It is the maximum value of fault current actually reached before the fuse blow out.

What is Pre-arcing time of a fuse?

• It is the time between the commencement of fault and the instant when cut-off occurs.

When a fault occurs, the fault current rises rapidly and generates heat in the fuse element. As the fault current reaches the cut off value, the fuse element melts and an arc is initiated. The time from the start of fault and to the instant when the arc is initiated is known as pre-arcing time. this value is generally very small typically 0.001 second. 

Read more: What are the advantages and disadvantages of fuses?

What is the Arcing time of a fuse?

• This is the time between the end of pre-arcing time and the instant when the arc is extinguished.
  

What is Total operating time of a fuse?

• It is the sum of pre-arcing time and arcing time

What is the Breaking Capacity of a fuse?

• It is the r.m.s. value of a. c. component of maximum prospective current that a fuse can deal with at rated service voltage.

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