If you've ever had to replace a fuse, you may have realised that there's a few different fuse speeds. In simple terms, 'fuse speed' tends to refer to the time between the moment that an overcurrent begins and the moment the fuse arcs and opens the circuits.
Most fuses can be considered to be fast acting, however there are also slow acting varieties, also known as 'motor fuses', 'time delay', 'slow blow', 'delayed action', etc and semiconductor protection versions, also known as 'ultra-rapid', 'solid state', 'rectifier', etc.
When it comes to official classifications though, you may be surprised to know that fuses are not classified in terms of 'speed' but more in terms of 'range' and 'application'. All fuses that are covered by the IEC standard Belong to a utilisation category and when selecting fuses, it's very important to get this right.
The IEC Utilisation Category Format
Fuses are marked with symbols denoting their particular application or characteristic.
First Letter (lower case)
The first, lower-case letter indicates the breaking range of the fuse.
"g" stands for full-range breaking capacity, meaning that the fuse is capable of breaking all overcurrents from its minimum melting current up to its breaking capacity. These fuses can protect from overloads and short circuits. Full-range breaking capacity fuses can be used as sole protective devices.
"a" stands for partial-range breaking capacity, meaning that the fuse is capable of only breaking high currents of a multiple of its rated current. Partial-range breaking capacity fuses are designed for short-circuit protection only, and are therefore used in combination with other devices providing protection against overcurrents. They are also frequently used for back-up protection of other switching devices having a lower breaking capacity (e.g. contactors or circuit breakers).
Second Letter (upper case)
The second, upper-case letter indicates the characteristic. These are related to the intended application. For example, ‘G’ relates to general applications (cable & line protection), ‘M’ relates to motor circuits, ‘R’ relates to rectifier or semiconductor protection and ‘B’ relates to mining applications. Sometimes, this part can be expressed with two letters such as ‘PV’ (Photovoltaic protection) or ‘Tr’ (Transformer protection).
A Selection of Current IEC Utilisation Categories used in Australia
Full range breaking capacity fuse for general application, mainly used for cable and line protection.
|Partial range breaking capacity fuse for the short circuit protection of motor circuits.|
Full range breaking capacity fuse for the protection of semiconductor devices (quicker than gS).
Partial range breaking capacity fuse for the short circuit protection of semiconductor devices.
Full range breaking capacity fuse for the protection of semiconductor devices for increased line utilisation. Combines gR and gG performance. Semiconductor protection against short circuits via the gR characteristic combined with cable protection against overload via the gG characteristic.
|Full range breaking capacity fuse for mining applications.|
Full range breaking capacity fuse for transformer protection, rated in transformer apparent power (kVA) instead of rated current (A).
Full range breaking capacity fuse for the protection of Photovoltaic systems.
Full range breaking capacity fuse for motor circuit protection, dual rated (widely used in the UK, Australia and South Africa.
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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!
DIRECTOR - JOHNSON ELECTRICAL SERVICES
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!
LAWRENCE AND HANSON
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.
ELECTRICAL MAINTENANCE AT BHP BILLITON
Thanks for ensuring that our order was delivered on time. Again, thank you for going the extra 8,000 km!
LOGISTICS OFFICER AT GRIDSENSE
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.
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.
EXPORT DEPT AT REXEL
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.
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