Fuse Selection – How to Prevent Disaster

Fuse Selection – How to Prevent Disaster

Choosing the right fuse for your application is vital. A fuse is a protective device so if it’s not selected with care, the level of protection that your circuit will experience may be compromised, leading to serious (& expensive) consequences.

However, identifying which fuse you need is not always the simplest of tasks. Many fuses look almost identical, yet are opposites in how they perform. Here are two examples of what can happen when the wrong fuse is selected for an application:

In this case, the incorrect fuses failed to safely interrupt a fault-current, resulting in the board & cables catching fire.

The heat from this explosion melted the perspex protective safety cover! 

So what's important to know so that you can avoid these situations?

Selecting the correct current and voltage rating and is obviously important however in these cases, the operator chose the incorrect ‘Utilisation Category’ and that is the main reason for these catastrophic events.

All fuses have two basic functions:

  • To interrupt and open a circuit in the event of an over-current
  • To protect the circuit from the effects of the maximum fault current in the event of a short circuit

However, fuses differ on when and how quickly they operate to fulfil these roles.

For example, for general cable and line protection, a fuse needs to tolerate a certain level of current fluctuation in the circuit as part of what is considered to be normal operations. Then when an over-current of a certain value occurs and is sustained for a certain period of time, the fuse is engineered so that the heat build-up melts its element and the fuse opens the circuit. These fuses are known as fast acting and are often marked with an ‘F’ or a ‘gG’. This is the most common performance group, or utilisation category.

When motors are included in a circuit, they experience a large in-rush current when turned on as the motor energises before settling down to a normal level. If you were to use a fast acting fuse, it would not be able to tolerate the energy during the start-up phase and the in-rush current would cause it to open the circuit. In this circumstance, the fuse would ‘nuisance blow’ and not enable the motor circuit to operate properly. Therefore, for circuits involving motors, fans, pumps etc, you need to use fuses known as ‘slow-acting’ or ‘motor-start’ and which have the designation ‘T’ or ‘aM’.

When protecting sensitive semiconductor components such as thyristors, such is their sensitivity to heat rise that you need to use fuses that operate within the first couple of cycles. These are known as ‘semiconductor’, ‘ultra-rapid’ or ‘solid-state’ fuses and are designated with ‘FF’, ‘aR’ and ‘gR’.

Imagine if you used a semiconductor fuse in a general protection or motor application. The fuse would blow instantly, making the circuit inoperable and wasting a lot of expensive fuses. Worse still, imagine using a general fast acting or motor start fuse to protect a semiconductor. The expensive semiconductor would be fried before the fuse ‘woke up’.

Some time ago, we became aware of a situation where a $60,000 thyristor stack was destroyed by a mild overload because the $30 fuse was chosen incorrectly – they used a common gG fuse instead of the required gR fuse.

Neglecting to check the type or ‘utilisation category’ of a selected fuse is the most common mistake that leads to catastrophic situations. We encourage you to take a moment and check these details. Not all fuses have the markings to show this information, in which case you’ll need to reference the manufacturers’ part number and technical datasheet.

Fuseco are fuse experts and have decades of experience in identifying fuses. Please contact Fuseco with the details of your fuse requirement and we will happily guide you through correct fuse identification & replacement.


Fuseco are experts at identifying fuse and we love to help our customers identify fuses & find replacements.

If you’re trying to identify a fuse, please contact the experts at FUSECO. We have 27 years of experience specialising in electrical products. Our friendly staff members will be willing to help you identify exactly what fuse you need.

Call us today for a quote and let FUSECO become your No.1 supplier of fuses.

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Fuse Products

  • For all orders over $100 (excl. GST & freight), freight is FIS (Free into Store).
  • For all orders under $100 (excl. GST & freight), a freight charge of $25 + GST is applicable.
  • Additional fees may apply for deliveries to the Northern Territory and remote areas.

All Other Products

  • Freight charges POA (Price on Application)
  • FOT (Customer nominates own carrier and accepts all charges)

Freight details

Fuseco can help! We provide a 24 hour 7 day a week service for customers who are experiencing a breakdown situation or need a fuse urgently after-hours or during the weekend.

To use this service, please call our after-hours number 0411 104 363 and one of our customer service team members will be available to assist you. Please note that an after-hours fee applies to this service.

Fuses shall be selected according to the following criteria. 

  • Maximum operational voltage – shall be equal or greater than the system operating voltage. 
  • Rated breaking capacity – shall be equal to or greater than the maximum fault current expected in the circuit downstream the fuse. 
  • Rated current – shall be equal to or greater than the continuous operating current of the circuit protected by the fuse. 
  • Breaking range – partial range or full range breaking capacity according to the type of protection required. 
  • Utilisation category – select according to the nature of equipment to be protected.

Fuses are in most cases marked with all the essential information required to select a replacement fuse or to enable you to select fuses for most common applications. Additional information, such as performance characteristics can be supplied by the fuse manufacturer. Standard markings are as follows:

  • Fuse standard, size and reference. This defines the operating performance and mechanical design of the fuse.
  • Voltage rating. Fuses may be operated up to the maximum voltage stated in the rating. Voltage ratings may be colour coded to reduce the risk of incorrect installation.
  • Current rating. This represents the value of the current that the fuse can carry continuously with out deterioration under specified conditions.
  • Rated breaking capacity. This is the maximum value of prospective current that a fuse is capable of breaking under standard conditions. In other words, the maximum amount of current that a fuse can tolerate without losing its physical integrity (physically breaking apart). Industrial fuses according to IEC 60269-2 have a minimum breaking capacity of A.C. 50kA and D.C 25kA respectively.
  • Breaking range and utilization category are indicated by letter codes. The first (lower case) letter indicates the breaking range, i.e. the range of prospective currents the fuse is able to break. The second (capital) letter indicates the utilization category, i.e. time-current characteristics for typical applications.
  • Fuse manufacturer or trademark.
  • Manufacturer’s product reference or part number, required for additional information on the fuse.

Additional markings may include:

  • Rated frequency if other than 50 or 60 Hz. 
  • Date of manufacture, useful to trace back product design changes.
  • Certification mark, asserting product quality by an independent certification body. 
  • Conformity mark, stating conformity to applicable national directives. 
  • Recycling mark, identifying responsible recycling organization. 

In most cases, people contact Fuseco when they need to replace an existing fuse that has blown. In such cases, it is paramount that either the identical fuse or an exact equivalent is provided. Care must be taken to make sure that the fuse provided is of the same utilisation category and has the same electrical performance of the original. If you need assistance with this, I welcome you to contact us and we would be very happy to assist you. Also, we provide many types of cross-reference charts on this website, wall charts and various tools that can assist you to identify equivalent fuse types.

Fuses are rated by current, voltage, breaking capacity (interrupt capability) and whether they are designed to operate on AC or DC circuits. The current rating of a fuse is the current that it can carry for indefinite time periods without opening. The voltage rating relates to the ability of the fuse to function and extinguish internal arcs when it opens. The breaking capacity is how large a short-circuit or fault current the fuse can interrupt or stop safely without allowing a continuing arc and without damaging the fuse body or fuse holder.


I called thru at 430pm EST and was put in contact with Sally in Vic! From the moment the call was answered Sally couldn’t do enough to try and help..... then she organised for Sydney to open up at 6am for me to collect the fuses. As a service-based company it was very refreshing to come across someone that went over and above to help us client back into production as quickly as we could!

Russell King


Michael, you asked me if I was happy with your service. Let me tell you that Fuseco had quoted and delivered the products via airfreight from Germany before our other suppliers returned our call. Outstanding!

Peter Stremski


I would like to acknowledge the exceptional service provided by one of your employees over the Xmas break. On Christmas day we lost a 22kV underground feed to a very important part of our business and were desperate for some replacement HV fuses. I found your emergency contact details on the web a and immediately called. The person who answered was very helpful and arranged an emergency transport to our site. The next day, we were back up and running! We are a remote operation 1800kms from the nearest city and average service is the norm.

Gregory Blair


Thanks for ensuring that our order was delivered on time. Again, thank you for going the extra 8,000 km!

Don Hajdu


I just wanted to let you know what great service your people gave us over the Christmas break and went to great lengths to make sure that we got the right fuses and that they were delivered on time. Dealing with your company a pleasure. Keep up the good work.

Kerry Prasad


I don’t normally do this but I feel compelled to thank you in writing. I have been in the electrical industry for 25 years and without a doubt the most competent and trustworthy supplier I have used over this period of time is Fuseco. This is a demanding industry and how your team keeps performing above expectations is exceptional to me.

Ross Adam


I have dealt with Fuseco for the last 6 years for all our fuse requirements and find they provide the highest quality service and on-going support to our business for our day to day operations and for emergency/ heatwave as they arise. During a heatwave event in January 2014, SA Power Networks had critical fuse demands. Fuseco were extremely responsive in expediting stock requirements and organising special air freights to meet our urgent demands. Their customer service is excellent and key KPI’s measured against the contract are always above target.

Peter Ashenden


Any company that can pull a rabbit out of a hat like that definitely has my attention!

Dane Branham


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