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We often find that people have a number of questions about when and how to use fuses for electrical circuit protection. Whether you need to know the basics, such as when to use a fuse, or to consider more complex issues. We have put together these FAQs to answer some of your queries.
Remember that our techincal team is always ready to answer whatever questions you might have.
What happens inside a fuse when it operates?
Thanks to the sealed fuse cartiridge the energy released during a short-circuit is contained within the body of the fuse.
What if a fuse fails to operate?
There is a lot of engineering design in a fuse to ensure that it operates safely in a given situation. Fuses often deal with huge overloads and protect circuit protection further down the system or equipment from the effects of such an overload. If it fails to operate then the results could be catastrophic, there could well be an explosion that would be dangerous for the equipment or anyone nearby.
Mis-application of a fuse is the major contributing factor to a fuse not operating in a faulted circuit. There are many factors to consider during fuse selection to ensure the correct device is used. It is critical that all circuit conditions are known to ensure the fuse will be able to operate safely. If there is any doubt in a fuse selection the manufacturer should be consulted.
This means that you should only deal with reputable manufacturers and wholesalers. You should also need to be aware of counterfeits or fake products and never buy products from trading websites where the supply chain cannot be known or websites that you don’t recognise. If something looks too good to be true, then it probably is too good to be true.
Fuses are a safety component and for that reason should only be purchased from known authorised distributors or directly from the manufacturer.
Can I use a fuse wire instead of a fuse?
While fuse wire will melt or vaporise and break the circuit, it will not protect against the effects of the overcurrent. Fuses often deal with very high overload currents which could cause an explosion, so it also needs to protect its environment including any equipment or people that may be nearby.
A fuse wire may be okay for lower overload, none critical low power applications, but it does not control the melting process or provide any level of safety.
Should I use a fuse or a circuit breaker?
Both devices will break the circuit if there is an overload or short circuit, and indeed they often work together. Fuses tend to be more cost effective than circuit breakers, but they do need replacing after they have operated, unlike circuit breakers that can be reset. Circuit breakers are also often 4-5 times the size of the equivalent fuse protective device.
In general fuses tend to be better at interrupting very high faults so they are often used before the panel / distribution board or consumer unit as an additional layer of protection. For example, a circuit breaker may have a breaking capacity of 5kA, so any fault current above that will destroy it. In comparison a fuse could have a breaking capacity of 33kA or even higher depending on its design.
Also, a fuse will not vaporise or explode in extreme fault conditions so it will not damage the electrical system or the equipment that it is protecting. This means that you will often use fuses further up the electrical distribution system in applications such as sub stations.
Every application is different and should be look at in detail to determine the best over current protective device.
If the fuse does not operate then it will typically last 20 - 30 years as long as it is operating within its design limitations.
If it is in a higher cyclic operating temperature i.e. very cold or very hot, then this can reduce its life. This means that you need to check the environment it will be used in. If it is destined for a hot climate, such as the Middle East where temperatures are regularly above 35oC then this could affect its lifespan. Similarly, hot industrial applications, such as in a foundry will have an effect.
However fuses can be selected and rated to take into account this conditions to reduce the effects of fatigue on the fuse due to heat. There are many factors that affect fuse life which is extremely difficult to predict. Every application is different and calculations can be done to ensure the fuse will provide good over current protection and provide a long service life.
Contact our team our team of electrical fuses experts should have any questions regarding the most suitable fuses to use for your application: buletechnical@eaton.com
What should I consider when selecting a fuse?
There are several factors that you need to consider. As outlined above extreme operating temperatures is one, but you should also think about the following:
Its system voltage. A fuse can only operate up to its specified voltage, so you can only use a 415V fuse rating where there is an operating voltage of 415V or less. Never use a fuse above its rated voltage.
The current rating. The continuous current within the circuit must be known and the fuse should be rated to carry this indefinitely. You also need to know whether there will be fluctuations or surges as equipment starts up. A good example is for starting motors where you will get an initial surge before the current settles down. It is important to understand what it is that the fuse will be protecting before you select it.
In addition, if you export equipment or work in different markets then the fuses will need to conform to the local standard.
To summarise different applications will need different solutions, so if you are uncertain then it is best to speak our team of electrical fuses experts: buletechnical@eaton.com
As the name suggests this is a vessel that holds the fuse. You can use it to connect the fuse to the circuit that it is protecting, and it can help make installation easier. It can also make it easier to remove the fuse and isolate the circuit for maintenance work. Whether you need a fuse holder or not will depend on the application.
