What is fuse rating?

Fuse rating is the maximum current that a fuse can safely carry before it blows or melts. It is usually expressed in amps (A) or milliamps (mA). 

For example, a 5A fuse can handle up to 5 amps of current, while a 500mA fuse can handle up to 500 milliamps of current.

The three C’s of overcurrent protection which are now known as Friemel’s Laws of Overcurrent Protection:

1. Interrupting rating (Capacity)

2. Component Protection

3. Selective Coordination

An understanding of these three key  electrical  overcurrent protection principles will lead to a safe, reliable and code compliant electrical system.

What happens if the fuse rating is too low or high?

It depends, For fuse rated current

 If fuse current rating is low, it's sure that it will be blow as soon as possible.

If fuse current rating is high, it may cannot blow even when the other electrical parts are broken.

For the fuse rated voltage,

At least it should be same as system voltage or higher.

If the fuse rated voltage is less than system voltage, it will blow ASAP when it's assemblied in circuit operation.

If the fuse rated voltage is too high, there is no very big influence, if there is not too big difference.

For example, If in a 380VDC system, 500VDC fuse could be used. Or if 500VDC fuse is not available, 800VDC ，1000VDC fuse is also OK to select in a circuit if in device there is enough space. 

Because for high speed fuse, rated voltage is bigger, rated current is bigger, then fuse will be with bigger size.

How fuse rating is calculated?

1), For motor circuit, if the fuse is used in main circuit, we should consider the fuse rated current is at least 1.6 times of main circuit operation current.

Voltage, same or higher than circuit operation rated voltage is OK.

If fuse is used in auxiliary loop(Also called the control loop), it will need the independent design. No fix data.

E.g: In a main circuit, customer use ABB Inverter. So 170E7727 is the main fuse to protect the contactor, IGBT etc.

What happens if you use the wrong fuse?

Normal case:  Non-stop fusing, or no fusing;

In extreme cases, if the fuse selection is too small, There is a high probability of fuse explosion, or other electronic component explosion.

 Which one is more dangerous, high voltage low current, or low voltage high current?

Obsolutely, it's high voltagae low current.

Fuse function in circuit:  When there is Overloading , short circuit in operation circuit, fuse will melt.

So current is a very key factor in fuse, 2nd is voltage.