FAQ – Our Most Frequently Asked Questions

Here are our 10 most frequently asked questions – and answers – about fuses.

Your questions answered – to submit your fuse related queries and comments, please email to profuseinternational@gmail.com.

Will a fuse still activate if it is too old?

YES! The older the fuse is, the faster it will activate!

Let's see how it works: Joule’s rule: current = temperature rise in the fuse element.

The rise of temperature is concentrated in restricted areas (below in red): they are weak point that melt in case of abnormal temperature rise:

With cycles and time, the worst thing that can occur is that restricted areas become too weak and the fuse will melt too quickly.

A fuse-link is a safe protection product.

Is it possible to make a mistake when replacing a fuse ?

It is the responsibility of the electrician. As a fuse base can receive a 10A fuse as well as a 25A, it is easy to mix them up. For most industrial fuses, however a special tool is required to remove the fuse. Only an electrician can remove it easily. It is the responsability of the electrician to check the fuse rating (written on the fuse body). It seems obvious but you need to have access to a fuse stock to make the mistake and not everybody has easy access to it. For a breaker, the situation is much more critical: Anybody with a screw driver can change the breaker settings including any workers in the factory fed-up with the breakers tripping. « The breaker trips at 160A? I’ll change it to 250A , no more problems… ». Protection has been lost and safety is compromised.

Does a breaker contain substances that are dangerous to the environment?

YES: many breakers do contain Cadmium even if they are RohS compliant.
  • Circuit breakers often take advantage of the encapsulated cadmium exemption per Annex 8 of the RosH directive.
  • A large scale production circuit breaker factory for live tank air insulated breakers consumes approximately 50 tons of SF6 gas each year. A deadtank circuit breaker factory consumes 10 times that amount.
Because of its environmental unfriendly attributes SF6 was included in the Kyoto Protocol with the objective of reducing emissions.

Is it difficult to select a fuse as there seem to be so many different types of fuses?

No! Instead of having to choose between 6 types of curves and 4 types of tripping modules as you would to select a breaker, fuses are easily sorted by application:
  • General use: gG type
  • Motor Protection: aM type
  • Power electronics protection: uR type
  • Photovoltaic applications: gPV type.
If you know your application, you just have to choose the related type of fuse and the necessary rating. Whatever, if you use an electrical software, the fuse selection, as the breaker selection, will be simple.

Can I save money with a breaker by decreasing the diameters of the cables?

This is a false economy: the smaller the cable, the higher the watt losses. Ultimately, by decreasing the cable size, you will lose more watts than your initial cable cost. Decreasing the cable will not save money!

Is it true that with a breaker I don’t need to hold stock of spare parts?

It is not completely true: Big breakers (ACB) are usually changeable: indeed, in case of damage to the breaker (after overloads or short-circuit), it must be changed very quickly. In that case, it is important to keep stocks of replacement breakers. This is true even for smaller breakers: manufacturers often advise maintening stocks of spare breakers in order to reach maintenance standards. In the case of fuses, your stock would usually fit inside a standard drawer!

Do I have to replace fuses all the time?

In normal conditions, a fuse never has to be replaced. If you do have to replace fuses, it is because:
  • An incident has occured (overload or short-circuit) that require investigation and must be solved before the installation is restarted.
  • The installation has a fundamental design problem and needs to be redesigned.
In both cases, a breaker wouldn’t help. Even worse, the temptation to immediately reset to « I » position after a tripping carries a significant risk: the breaker provides confidence to immediately restart but the problem still exists (or if dormant will occur again). This is potentially very dangerous and would not meet with the approval of a professional electrician. Please keep in mind:
  • Each time a breaker trips, there is an increased risk of internal destruction of the breaker.
  • With a fuse, you renew your installation after replacement.

When were fuses first invented?

Exactly when a fuse first appeared in the field of electricity is still not known.

What is certain is that in the 1860s platinum wires were used to protect undersea cables.

The appearance of the first enclosed fuse that was designed to melt has been the object of some discussion. History books tell us that it all began with a patent taken out by Thomas Edison in 1880. But it has also been suggested that the great English physicist Sir Joseph Swan played a major role in the early development of fuses.

What is the benefit of current limiting by fuses?

The energy that the installed protective device lets-through determines the required robustness of the installation and of the protected components. A fuse interrupts the short-circuit current. Consequently, it only lets through a very small amount of energy (I²t). A 100A fuse, 20 kA breaking capacity, 415 V reduces the initial default current from 4 000 000 A²s to 46 000 A²s. This reduction is illustrated below. The volume illustrates the effect of the fuse current limitation function. It consequently offers the opportunity to use smaller components below the fuse and so to build a more compact and cost effective installation.

How does the fuse to control energy?

When a short-circuit current occurs, it releases a large amount of energy. This energy can either:
  • Be confined in the body of the installed protective device.
  • Be released into the environment
The second option makes the selection of the protective device installation easier, but the installation of the device needs to be thought through carefully. The ionised gas emission can reinitiate the short-circuit of the protective device. Moreover the pressure following the short-circuit can force the control panel cover to open. With a fuse, the energy is absorbed by the quartz particles present inside the fuse body. It is dissipated inside the fuse body which eliminates any potential material being expelled. In summary a fuse is a safe electrical protection device.