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I found this high voltage fuse on the transformer in a microwave. It seemed a good idea to blow it for educational reasons.
Note that most modern home-microwave magnetrons do not use beryllium oxide insulators, despite the negatarian folklore. But always play safe and assume the worst.
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While dismantling a microwave to take the transformer out for a video where i showed just how dangerous these things are and why you shouldn't really play about with these in their original high voltage form, i found this fuse on the transformer and i thought it's quite interesting Because it's a high voltage fuse and it appears to have a very fine wire with a spring to pull it open. So i thought it would be quite fun to blow this fuse, not necessarily with high voltage, because an amp is an amp and you can use low voltage as well. So, let's get this out the way that big lump of death and before i do that, i just want to mention something. This is the magnetron there's the thermal cut out, heatsink filter, section and then the actual exciting bit in the middle, which is complete rocket science.

But i want to mention: there's a common thing goes around to say, oh, be careful about this. It's beryllium oxide. I just want to say it's very unlikely to be beryllium oxide because that's very expensive and you might well find that in super high power devices, but most domestic microwaves with absolutely no warning stickers around things saying beryllium oxide, it's more likely to be aluminium oxide with A touch of chromium oxide, which gives it that distinctive, pink color and it doesn't pose the same hazards. Obviously you should treat it with precaution anyway, but in most instances this is not likely to be beryllium oxide right on with the fuse blowing.

So i'm going to set this up in a vice and are going to get you down close to it, so you can see what happens when this blows. One moment please and the experiment is ready to go so at the left hand, side of this trough is a very thin fuse wire at the right hand, side there's a spring pulling a bit of tension that let's blow it and see how much movement there is. Oh, that's quite a lot of movement that was interesting. I didn't think it was going to go back that far, but that's designed to break that high voltage arc and extinguish it.

So there you go. That's the inside of a high voltage fuse blowing quite interesting. Indeed.

16 thoughts on “Blowing a high voltage fuse”
  1. Avataaar/Circle Created with python_avatars BedsitBob says:

    On the subject of high voltages, could you do a video on why the grid uses odd voltages, like 132,000 and 66,000, rather than round figures, like 100,000 and 50,000?

  2. Avataaar/Circle Created with python_avatars DrHarryT says:

    How is it possible to have a video published minutes ago today have comments that say 10 days ago?????

  3. Avataaar/Circle Created with python_avatars Steven Raith says:

    That is, from a relative layman's perspective, quite neat – the risk of high voltage over normal voltages is arcing, so make a fuse that can't arc.

    Nicely designed.

  4. Avataaar/Circle Created with python_avatars J P says:

    Some types of fuses in medium voltage substations fire a spike out of the end cap when the fuse blows. The spike pushes a lever which shuts off all 3 phases. Would be good to see Clive play with one of these!

  5. Avataaar/Circle Created with python_avatars Anonymous Kultist says:

    It's just not the same without the oddly sinister pseudo whisper of "I popped iiiiit".

  6. Avataaar/Circle Created with python_avatars mweverett says:

    We used high power UHF tubes at work that did indeed have Beryllium oxide. As long as you left them alone there is no chance of poisoning. Only the dust would be an issue, and you would not be stupid enough to do that, right?

  7. Avataaar/Circle Created with python_avatars Rob Smith says:

    Now we've seen Clive blow a low amp, high voltage fuse hands up all who want to see him blow a high current open blade fuse. Not too big a fuse, lets settle for one rates at about 10kA.

  8. Avataaar/Circle Created with python_avatars Richard Smith says:

    The further the spring travels after blowing, the higher the voltage rating of the fuse, I assume.

  9. Avataaar/Circle Created with python_avatars Today on the Bench says:

    Well, that separated quickly, only 1 frame of the wire glowing, another where the spring is almost fully retreated with a hefty bit of motion blur, and the frame after that it is all done.
    Should find one more and record at a bit higher FPS and slow the footage down to better show it.

  10. Avataaar/Circle Created with python_avatars Jason Kuehl says:

    I'm not sure exactly what I expected from that fuse, but was still surprised by the amount of motion. Simple and effective, the way things should be! ๐Ÿ™‚

  11. Avataaar/Circle Created with python_avatars cptcrogge says:

    Its so simple yet effective, the big distance comes in handy if you encounter a massive amount of power.

  12. Avataaar/Circle Created with python_avatars Stephen Eyles says:

    Nice! I found a nice High Voltage fuse at work the other day. It is about 8 inches long, 3 inches across. Rating: 2.5kV, 250A ๐Ÿ˜€

  13. Avataaar/Circle Created with python_avatars devttyUSB0 says:

    I saw this fuse in the live stream and was wondering if a video would be made. It's quite nice, no arc supressors. Any idea what kind of load this thing would have to break? What did it take to blow the fuse?

  14. Avataaar/Circle Created with python_avatars zh84 says:

    If only Lauri Vuohensilta of the Hydraulic Press Channel lived a bit nearer you could have borrowed his high speed camera.

  15. Avataaar/Circle Created with python_avatars ParedCheese says:

    Cool! ๐Ÿ‘
    Would have been interesting to see how big the arc would have been with a HV source. ๐Ÿค”

  16. Avataaar/Circle Created with python_avatars Peter Stevens says:

    Does that style of hv fuse have some sort of advantage compared to one filled with sand? size maybe?

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