I have seen a board and I wonder to know what would be the advantage of having capacitor in parallel with fuse.enter image description here

  • \$\begingroup\$ When a fuse is in parallel with a capacitor the capacitor will be shorted until the fuse blows. If a fuse blows you want a circuit to be off and not still connected via a capacitor. Your question makes no sense as it makes no sense to connect a fuse in parallel with a capacitor. The fact that a fuse is close to a capacitor doesn't mean they're in parallel. If the fuse and cap are really in parallel on this board then whoever designed it like that has to explain why it needs to be like that. \$\endgroup\$ Commented Sep 5, 2019 at 9:23
  • \$\begingroup\$ @Bimpelrekkie It doesn't make sense to me either, especially for AC, but this could be a DC rail. \$\endgroup\$
    – HandyHowie
    Commented Sep 5, 2019 at 9:28
  • \$\begingroup\$ I assume the question is about the fuses next to each of the blue contact block on the bottom and right edges. There is an electrolytic which may or may not be in parallel with the fuse, and a yellow epoxy-encapsulated component which looks like it is soldered to the fuse. Maybe it's an attempt to make sure the fuse blows on DC but not AC? \$\endgroup\$
    – Jack B
    Commented Sep 5, 2019 at 9:37
  • 2
    \$\begingroup\$ @JackB: It is about the ceramic disk capacitors soldered right onto the fuses. \$\endgroup\$
    – JRE
    Commented Sep 5, 2019 at 15:50
  • \$\begingroup\$ Looks like a nice fuse puller handle to me. \$\endgroup\$
    – Marla
    Commented Sep 5, 2019 at 18:03

2 Answers 2


The capacitor is placed for protecting fuse in switch on/off system. Most loads are inductive such as motors and light bulbs, and in switching on or off, they will make a huge voltage from inductor equation, in switching on, this voltage will cause a huge current in a very little time, this can break your fuse without a SC, etc By using this capacitor (typically ceramic) you can filter this current and protect your fuse from damaging from this current.

  • 1
    \$\begingroup\$ This is what came to my mind if you couldn't get ahold of slow blow fuses. Tacky though. \$\endgroup\$
    – DKNguyen
    Commented Sep 5, 2019 at 15:39

Are you sure they are capacitors and not some polyfuse or thermistor?

This doesn't look like your standard manufacturer bodge, but more like an amateur fix which may explain why there are more questions than answers.

Soldering to a fuse is a tacky way to attach something across those two points. Why not solder to the holder or the pins on the reverse side?

Cheap small fuses are often secured to the element inside by nothing more than solder and the end caps by adhesive. In my experience, even briefly, soldering to the end cap causes the adhesive to fail and may reflow the internal soldered joint potentially upsetting the element causing the connection to break. Not all the time but enough that i consider this technique janky.

Also, is the user expected to solder a "capacitor" to the new fuse if the old one blows?


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