High voltage fuse: it’s rubbish!

Excuse my words, I am so upset … I give you my story. My name is Lothar Schmitz, I am 39 and my job is Service electrical maintenance Manager. Our main customers are large industrial sites.

We had a shortcircuit in one of our substation of our network: one 10kV high voltage fuse melted. A guy of my team quickly reached the site and changed the blown fuse and re energized the feedind circuit …

Medium Voltage Fuses

Two weeks later, same problem occurred in the same cubicle but this time it’s the other phase fuse which blew up because in fact it has been damaged at the time of the first fault.
My agent of course did come back and decided to replace the 2 other high voltage fuse s … unfortunately during the mounting, he broke one fuse down, had to clean the substation floor.

This little incident was becoming a real big problem because he did not have any other in stock and with a downstream production  with no energy !


* 1,5 man day lost
* Communication problems linked with production losses
* Penalties due to the customer of 11500€

Now, you understand why I am upset about high voltage fuse and this is not the fist time. I don’t think I am the only one and I propose to share our experiences. Please use the comment area below …

Lothar Schmitz


  • As far I know, most manufacturers advise replacing all the fuses at the same time although just one phase blows, because those which appear to be fine could also be damaged. However this suposses an extra cost that many customers do not always want to assume.

    • but i think so in all indutries all the electrical engineer do the same thing which this person did they only change the demaged one but its created proplem because when ever short circuit occured its offten disturb the other one


  • You should use the Sandc dropout fuses with one inteliruptor for the protection,
    this are very well coordinated and fuses never blow with temp. falts.
    because inteliruptor take care of the temp. falts.

    • Thank you for your suggestion.
      I guess dropout fuses with intelirupter is for overhead lines.
      I have to protect transformers and cables.
      So, apart from the fact that it is not easy to change an existing installation, I am wondering if this solution could be applied for our type of application.

  • try to check the feeder from climbing vegetations downstream and thighting terminals especially at disconnects/isolators and other terminal equipments such as current transfomers and potential transformers.also,change fuses at he same time and balace loads evenly if practicable

  • I would agree with Wahab’s observations. It is standard practice in my experience to replace the whole set of fuses whenever an HV fuse trips. It makes sense to keep a quantity of spares.

  • Maybe HV fuses are bullshit these days but probabaly not at the time when the designer was summing up the cost diffence between a HV fuse or CB solution.


  • It was drummed into me as an apprentice to always replace all phase fuses when one failed. That was over 40 years ago and it has worked well for me over the years. The fuse replacement cost and the time lost is the lesser of two evils when you have to attend to a similar fault due to the weakened fuses.

  • You say that you had a short circuit in one of your substations. I would imagine that fault would have been between two phases. The resulting short-circuit current would have been though at least two fuses at the point of failure, therefore requiring at least two fuses to be replaced. As everyone else has said it is best practice to replace all fuses on that circuit. CB’s although resettable are not neccesarily better than traditional fuses as the cause of a fault cannot always be traced to a particular phase. With the correct co-ordination, fuses will give years of uninterupted service at a fraction of the cost and physical size of CB’s.

  • High Voltage fuses are the main component of many power distribution installtions. Typical installations have these types of fuses installed in a 15KV air switch that typically connects to a transformer which in turn is connected to a lower voltage bus and feeder breakers. The 15 KV air switch is sometimes fed from a 15 KV breaker upstream. It is unusual to have these fuses blow, however, when they do as you describe, you should test the affected circuit and understand why the short circuit happened or what caused it before you proceed in replacing the fuse/s. You should insiste on finding the problem and the root cause prior to rushing to replace the fuse. After testing and understanding of the problem, you can proceed to replacing all fuses at the same time. They call this “group replacement”. It is always a good idea to do so. I hope this helps.

    IEEE Member

  • What i always make to solve such a problem it’s installing an isolated filament of cable. Its a risk but solves my problem. Its always a question of money vs time. the question in this case it’s “how much do you lose for having the system down”?

    Good luck

      • I absolutely agree with you that it’s a bad idea to install an isolated filament of cable. It is more safer to replace the right fuse size. Thanks guys for excellent discussion!

    • octavio this is very wrong. You gonna make things worst by that and burn whole system.This is the reason we but fuses.

  • It’s sound practice to change HV fuses in threes, the reason for this is:
    Assuming you are protecting a Transformer, a fault on red phase will be also supplied with fault current via the HV winding of the transformer, from the other two phases/fuses, however the fault currents in the other phases will be less due to the impedance of the winding.
    These lesser values of fault current still adversely affect the fuses, which are basically layers of glass which melt with current flow.
    The red phase fuse blows first, tripping the switch, but the others are damaged enough to blow later on normal load current
    Hope this helps

  • Replacing all the fuses and having one set spare has been standard practice, anything else is inviting troubles.
    Fuses are much better than circuit breaker for limiting the fault level and let-through energy in the event of a fault but the price to pay is the requirement for having to replace them when they have operated.
    We all learn by mistakes!

  • Replacing a fuse with a section of cable at HV is an utterly idiotic thing to encourage. I struggle to think of scenario whereby this would be advisable.

  • Yes yes of course change all 3 fuses.
    NO NO NO don’t just try one back. You never said if you found a fault. It may not be just the other fuse going down but an intermittent fault.
    Any self respecting maintenance manager has to make sure he has suitable number of spares so in this case Lothar I think its you that is to blame.
    Fuses are expensive but not compared to CB’s and CB and protection does need to be maintained so you must look at whole life cost of the installation.
    Octavio I just don’t understand the use of a cable as a fuse.. Scary very scary
    It does always worry me that so many people are operatingHV systems with no experience.

  • Dear Sir
    I do not agree that High voltage fuse is a Bullshit. It all depends up on the selection of fuse and its quality. Melted fuse are due to some other problems, like overvoltage flow in that circuit, Phase unbalance due to differenence in phases connected in that circuit etc. This phenomina happens in directional O.C. too when phase displacement takes place.

  • …….”Penalties due to the customer of 11500€” you must improve your stock strategy or the contract

  • Cinceramente cuando se pretende ganar tiempo en la recuperacion del servicio localizar rapidamente una falla a tierra del tipo de transitorias y encontrar un defecto fase a fase, lo pricipal es utulizar un interruptor automatico, con istancia remota del mismo. todos esos tiempos se minimizan y asegura un largo tiempo de libre mantenimiento y de ser alguno a de ser programado este…

    • I propose the following translation of javier hernan soarez comment (feel free to propose a more precise one) :

      “Sincerely if you want to reduce the time to recover normal service, to quickly locate a ground fault of transient type, or to find a phase to phase fault, the best is to use a circuit breaker with remote control. All the above times will be reduced, leaving you with more time free for other maintenance operations needed or programmed …”

    • jungarcia
      I think changing only the fuse wont solve the problem ,Finding the cause why it blown could be time consuming but its cost effective .first find the wiring diagram and trouble shoots if theres any grounded wires or worn out wirings .Are installation in proper ly insulated .Or is there any over loading , Its atime consuming task but it will help a lot

      • Sorry, but you couldn’t replace burned fuse, before you investigate the reason it burned.
        That why is fuse, to protect malfunctions.

  • I have had a number of reactions from people in the US and the UK, who explained to me that the term “bullshit” I originally used in the title of this article has a very strong and very hard meaning for “real” english speakers, which I was not aware of, as an english speaker as a foreign language. Following their suggestion, I decided to modify the title, to use “rubbish” in replacement, which still has the strong meaning meant by Lothar in his article.

    Laurent M, moderator

  • That as a good move Laurent changing the wording as its much better. Its scares me when I see crazy things like nails and bits of metal used to replace fuses. Its painful when you still the cost and time implication of having a faulty fuse so selecting a good quality one is cheaper in the long run.

  • Hi
    Let me tell my opinion. High Voltage Fuse, is used in measurement cubicles for to protect VT (voltage transformer). AS per symptoms you described, it is malfunction in VT or somewhere around.
    As you know VT is 110/rootsq of 3. When a earthfault appear, it raise voltage from 66V to 110V and activate protection. So here you must see your fault in system. If I’m wrong please tell me.
    Pay attention! Where else you have HV fuse?

    • You are right. There also are HV fuses protecting VTs. But in this case, it were fuses protecting MV/LV power transformer.

      • OK. Lets see what fuses like protecting element are? They anyway protect against earthfault or overburden. It is good to know when fuse burned. Keep in mind, a start up (switch on) of transformer, take around 11xInominal, for magnetizing current. In this purpose there is use of ‘slow acting’ fuses. To overpass, transient time. Your symptoms, you described, show this kind of fault. You tell it burned two times in a gap of two weeks.There is some transient moment, if switch complete device, or maybe you have downstream an earth fault. Keep in mind, earth fault protection must have, lower delay time, than time of fuses to burn.This is so named ‘selectivity of protection’. That why, look in catalog of fuse, graphic of acting curve, and extract time of delay of acting.
        Many people don’t look at this, because it is matter of settings, given in separate study of electrical side of plant. Many people, during maintenance, don’t look at these things, decalibrate protection selectivity, and have your case: protection act on higher level.
        That why one of the first things, you must see your downstream earth fault protection settings.
        I think if you read two times this, it will be clear for you.
        If it work for ever, you must find the reason of burning, for yourself, for your future experience.
        I’m here to discuss, if need. So again divide cases: was it turn off and on, of complete transformer, or fuse burn in the time of normal running of plant.Very important.

  • I am not an electrician but in my view it is better to keep the fuse and my reason is this.

    If a circuit breaker goes & there is no electrician the production or managers will try to reset & will continue until the kill the lot.

    If a fuse goes they will wait for the electrician.

    The problem you have is protocol, when a fuse goes acertain why if possible (could be age) & rectify.

    Change all the fuses in the set, at least 1 complete set of spares kept on site (sealed) and if used replaced immediately.

    So Lothar the problem is not the fuse IMO it is the maintenance systems in place


  • Yes mistakes do happen but only by following the simple rules and basics of installations all time cost and details should’ve being prevented.Believe me its for your own safety.

  • we use voltage transformers when we go in another country, most asian countries use 220 volts`~;

  • “Two weeks later, same problem occurred in the same cubicle but this time it’s the other phase fuse which blew up because in fact it has been damaged at the time of the first fault”

    How can you be so sure that the other fuse has been damaged also at the time of the first fault? If it was also damaged, then the system was running in “single phasing” after replacing the first fuse and IT TOOK THEM TWO (*****) WEEKS before they found out? You said that your customers are large industrial plants? I wonder what kind of loads these plants have that it managed to function despite single-phasing.

  • Changing the whole set of high voltage fuses will definitely reduce the risk of having a fuse to blow up after a short period of time, especially if all fuses were installed at the same time. make sure to keep enough fuses as spares for emergency cases.

  • Hey there! I’ve been reading your web site for a long time now and finally got the bravery to go ahead and give you a shout out from Humble Texas! Just wanted to say keep up the great work!

  • High voltage current limiting fuses are still the best protection we have. No circuit breaker can compite with such a fuse. The reason is the current limiting capability of the fuse. If you do not know the reason what operated the fuse, fase to earth-fault or fase to fase fault, it is basic to do two things: Try to identify what caused the fault and change all three fuses. If it was a fase to fase fault, at least the other two fuses are damaged and might operate later on. Usually they will operate when you energize the transformer again, because of the in-rush current when magnetizing the core. What you will have to do very urgently is establish a propper maintenance program which includes to have spare fuses in stock and make it a rule to change all three fuse. If you have the resistence value of the fuses you can later on measure them in order to assure that the fuses which did not operated are in service condition or wheather they are damaged. I am sorry to say so but who is to blame is: Lothar Schmitz, Service electrical maintenance Manager.
    ACEMSA, S.A.

  • Coming back after a looong time to my first love of MV fuses, after reading these posts (and some others) , I wonder wether MV fuses still have a long future facing them.
    Which applications , usages, will still request fuses, and not be wiped out by breakers ?
    In which countries are they still widely used ?
    Is it easy to find spares ?

    It seems that all major manufacturers have progressively dropped these productions ? Are there any manufacturers covering the world and being able to deliver spares, if I specify their fuses in new projects ?
    I know it is a lot of questions, … any hint to any of them is welcome !!

  • No one mentions the fact that fuses can clear a fault much faster than a breaker, helping to minimize the effects of an arc flash incident.

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