Questions regarding physical fuses. Fuses are a safety device consisting of a strip of wire that melts and breaks an electric circuit if the current exceeds a safe level. PPTC, PTC, and Polyfuse questions should use the Polyfuse Tag. Please keep in mind that repair questions are typically closed if ...

learn more… | top users | synonyms (1)

25
votes
3answers
3k views

Why did my fuse not blow?

I purchased a few fuses to get familiar with their workings, and I was surprised to see that the 100mA fast-blowing fuses I bought happily conducted up to 215mA (6V power supply, 10\$\Omega\$ ...
14
votes
4answers
5k views

What not to do with a Multimeter

So I just bought and installed a new fuse for an analog multimeter I scored for free and now it works like a charm. The new fuse is the same rating as the blown one I found inside, which is 0.5A ...
12
votes
5answers
10k views

Fuses: What are the practical differences between Ceramic and Glass cartridge fuses

What are the practical differences between ceramic and glass tube cartridge fuses? I am trying to find new fuses for a piece of consumer electronics. The original fuses are going out of production. ...
10
votes
2answers
251 views

How to ensure my device is safe for every day use?

I have put together a simple wake up light. It has an external powersupply, at the moment rated 7V and 600mA. Inside it has Arduino and bunch of LEDs controlled by a MOSFET. It works fine at the ...
9
votes
1answer
329 views

Understanding fuse specs

Can somebody please help me in understanding the fuse specifications. Actually i went through many fuse parameters. I am getting cofused between the hold current and the cut-off current since there is ...
8
votes
3answers
703 views

Can a fuse be placed after a load?

Considering that the regular treatment of a fuse is to place it on the positive side, "before" a load, is this just common practice, or is it backed by an actual reason? Can a fuse be placed on the ...
8
votes
4answers
5k views

How do I choose a fuse? Fusible Links vs Polyfuse?

I realise this is an extremely broad subject area but I need to know how to choose a fuse to protect a circuit. Recently, a cheap PSU of a friend's blew up quite spectacularly (the two primary ...
8
votes
3answers
317 views

Why might a multimeter ask for “wrong” fuse sizes?

Why might a multimeter ask for the "wrong" sizes of fuses? On the front of my Fluke 87 multimeter, the two probe ports for amperage are labeled as fused at 10A (max) and 400mA (max). When opening the ...
8
votes
3answers
435 views

Blowing a Fuse to Permanently Disable Functionality

Certain electrical designs require permanently disabling hardware functionality on the fly. Sending an overcurrent to a weak fuse may be a method for accomplishing this, breaking the circuit in a ...
7
votes
5answers
28k views

Slow Blow vs Fast Acting Fuse

Is there any way to tell the difference between a slow blow and a fast acting Fuse? I had one blow in my amp and I know its 125v 5a, but i'm not sure if it is a slow blow or fast acting fuse. Is ...
7
votes
4answers
3k views

Fuse blowing in 12 multimeters rated for 200mA, only measuring 12.5mA. Why?

I'm a high school electronics teacher and while doing a lab on Ohm's Law we just blew the fuses in 12 out of 18 brand new digital multimeters while measuring current, and no the meters were not hooked ...
7
votes
3answers
1k views

Cooper Bussmann's screw-in Edison-base mini breakers aren't for inductive loads. What does “inductive” mean?

I'm thinking of buying some Edison-base screw-in miniature circuit breakers to replace some of the fuses in my house. There are some made by Connecticut Electric and some made by Cooper Bussmann. ...
6
votes
3answers
2k views

How do I measure startup/inrush current?

I have some small devices that draw 20mA. I'd like to add a resettable (PPTC) fuse to them but I am not sure what value to select. My thought is I need to find a value that will tolerate the startup ...
6
votes
1answer
756 views

'Voltage Fuse' or better

I have a power supply with multiple outputs (5v, 12, 24v) According to the manufacture (and after testing) there must be a minimum load on the PSU for it to supply the stated voltages. Without a ...
6
votes
3answers
6k views

Should I use slow fuse or fast fuse?

When I design something or going to add a fuse to place where fuse isn't used now, should I prefer slow or fast fuse? I understand that this depends on situation, but I'd like to hear what do you ...
6
votes
1answer
364 views

Resettable Fuse: Do they have a “Reset” limit?

Sorry for the confusing question, but for PTC's or Resettable Fuses such as something like this: http://www.sparkfun.com/products/8357 Is there a "limit" on how many......I guess "resets" it can ...
6
votes
3answers
110 views

How do I size fuses to handle sudden changes in AC line voltage into a capacitive load?

Suppose I have a rectifier on the AC line, followed by some caps and a load. simulate this circuit – Schematic created using CircuitLab If the AC line is suddenly increased, there's a ...
5
votes
3answers
428 views

Why isn't ammeter protected with a fuse

Why is it that the ammeter with low current (200mA) limit are fused and not the 20A one? I recently lost a multimeter because i connected the ammeter in parallel by mistake. Edit: All the ammeters i ...
5
votes
5answers
1k views

Is it possible to quantify electric power consumption on a fuse?

If you have a common fuse is there way quantify the power consumption which is flowing through this fuse. Or could you replace the fuse with something that measures the power consumption but still ...
5
votes
5answers
11k views

Why does fuse blow up sometimes?

Sometimes once in a year, either one of main fuses or a fuse in room blow up due to something. What is the cause of this? Why do we even use fuses? Is it because the voltage doesn't stay at 220V all ...
5
votes
3answers
805 views

Replacing SMD Fuses without access to schematics

I'm curious to know if there is a sane way to determine the specifications of a blown SMD fuse without resorting to manufactures schematics / repair manuals. In my particular case there are no ...
5
votes
3answers
134 views

Given metal dimensions and material, is it possible to determine the maximum current that the structure can handle? [semiconductor processing]

I have a linewidth structure that has very low resistance. I want to know the maximum current that this structure can handle. Since the resistance of the metal is so low, it's hard to measure the ...
4
votes
3answers
299 views

Building a power supply, want to stay alive

I am building a power supply for a very old laptop. The circuit uses a transformer (220 V primary to 15 V secondary, 33 VA) and that worries me a little. (Please note that I an enthusiast and so far I ...
4
votes
3answers
2k views

When should you use a fuse?

When is it actually practical to use a fuse? Like lets say your building a robot using an Arduino.....what area would you want to protect the most with a fuse? I mean do they even make fuses that ...
4
votes
1answer
187 views

How do I know whether a fuse is a DC fuse or an AC fuse?

For example, I want to buy a 10A 50V DC fuse and a 10A 220V AC fuse online. Which website(s) should I go ? I tried on Mcmaster, but I could not get clear enough information of whether the fuse is an ...
3
votes
4answers
4k views

what size of copper wire can act as a 150A fuse?

If I would like to use a piece of copper wire as a 150A fuse, what size of wire should I use? It doesn't have to be 150A very accurately, the parameters I need the wire to meet are: it needs to ...
3
votes
2answers
454 views

Designing with fuses…when to use?

Most circuits that I have designed in the past deal with low voltages...sensors, communicating with other chips, etc. When would I need to consider the addition of fuses into my designs? Sometimes I ...
3
votes
6answers
6k views

How does a fuse blow at its current rating, regardless of voltage?

I know from reading elsewhere that it's safe to use a fuse with a higher voltage rating when replacing one, so long as the current rating and reaction speed is the same. For example, if a fuse is ...
3
votes
3answers
278 views

Are PTC fuses called some other way?

I recently learnt about the existence of PTC fuses, and I'd like to use one for an USB power supply I'm building. I guess there are PTC fuses on the PC side, but you never know. I went happily to buy ...
3
votes
4answers
1k views

Need help debugging my project: Fuses popping like crazy, but I can't find the reason why

I recently made a voltage and current controlled supply from a kit I found. It worked for about 15 minutes and then fuses started popping. Unfortunately, I have no idea why, because power supply ...
3
votes
5answers
1k views

How do you use a fuse with a rating of Amp-Hours?

Sorry, this may be me being slow, but... An amp-hour is 1 amp over 1 hour - simple enough. Now I have 2 fuses - one is rated in amps, the other in amp-hours. Can I I use one in place of the other? ...
3
votes
1answer
123 views

Question regarding fuses

What is the difference between thermal fuse and MOV and polyfuse.Which is faster and also which companies produce polyfuse, especially in Asia. I have to search for a component that can save my ...
3
votes
2answers
517 views

transformer blows fuse at no load

I'm building a multi channel power amp and I am having trouble with the power supply. I'm in Europe, so I've got 230v mains and I'm running into a transformer which brings it down to 60v. The ...
3
votes
2answers
1k views

Why do PTC fuses have different voltage ratings depending on package size / hold current?

I've been trying to figure out the PTC fuse I want to use in a little automotive power supply circuit and I'm a little disconcerted by the max Vdc ratings most of these things have. For instance, ...
3
votes
1answer
187 views

How can I protect the amplifier behind a headphone jack when interfacing with external circuitry?

I am wanting to mess with the output of my guitar amp. Not actually opening it up, just taking the headphone-output and connecting it to a breadboard and such. What form of protection, if any, ...
3
votes
1answer
295 views

Why use a double fuse for a relay-controlled heater?

After this question, another refrigerator "mistery" :-) This is the schematic of a no-frost refrigerator that I had to fix because the no-frost system failed and a huge quantity of ice clogged the ...
2
votes
3answers
776 views

How can I design a robust and professional power supply circuit?

I'm planning on doing a large project that would include an ARM microcontroller @ 50 MHz interfacing with a graphic LCD, user buttons, some sensors and some actuators (DC motors, valves) controlled ...
2
votes
5answers
503 views

Why do 0.02A fuses not protect a person? Why no protection from shocks?

I understand the user here so that fuses do not protect people from shocks. I am planning to put put fuses such as fast-blown fuses and PPTC fuses around all kind of positions such as ...
2
votes
1answer
610 views

Do fuse blow on ampere or effect?

I have a faulty car (bad central locking engines) and a fuse is blowing every time I open/lock the it. I'm looking to do a quick fix, and just replace it with an automatic fuse. The car runs on ~12V, ...
2
votes
2answers
151 views

Negative Voltage Breakers?

I've been reading a bit on negative voltage, but I have a question that will probably reveal some ignorance, so I apologize ahead of time. If someone tells me that they want a (2) 5A breakers, (1) ...
2
votes
1answer
4k views

How to check if my multimeter's fuse is damaged?

I recently bought a cheap multimeter. I played around measuring stuff on simple circuits and I think I managed to damage it as I don't seem to be able to measure current anymore (always get zero ...
2
votes
1answer
183 views

Will an opening fuse cause an inductive kick, or not?

I'm looking at designing a high-current crowbar circuit. We need to blow a 1400A fuse on demand. One question that has arisen is, what about inductive kick? If you short a large capacitor through a ...
2
votes
4answers
281 views

Overload protection for battery

My 6-year-old son has shown some interest in electronics, and I thought I'd get him some basic components (motors, LEDs, buzzers, etc) and let him experiment (using alligator clips and the like -- no ...
2
votes
1answer
2k views

What does 3AG mean in “Fuse Block 3AG”?

I have read from a vendor website. It mentions 3AG fuse block. What does 3AG mean?
2
votes
1answer
192 views

Are those some kind of timed-resetting fuses in DMMs?

Yesterday, I did something dumb, in a hurry. I wanted to check the AC voltage at the terminals of a hair-dryer, to determine the voltage being applied to the terminals of the AC fan behind it. ...
2
votes
2answers
894 views

Low value manually resettable adjustable electronic fuse

I might be asking for too much with this one, but I hope it is out there. I would like a fuse that can be reset, but not automatically. I need to be able to know that the fuse is blowing and with a ...
2
votes
3answers
983 views

How do glass tube fuses work?

This may be the an unspeakably stupid question for an electrical/computer engineering student to ask, but I ran across a few parts I didn't recognize (which, after some research, I found out were ...
2
votes
2answers
519 views

Should a fuse with the correct amps, but is physically too small, still power my stereo unit?

I'm not sure if I'm asking the right kind of question for this site. But if someone could help me, I'd be grateful: I blew a 125V 2.5A fuse in my home stereo head unit. I couldn't find that fuse at ...
2
votes
1answer
112 views

Computing ampacity a of small fuse from change in temp on breakdown

I'm trying to design an experiment for an entry-level electronics course involving burning out fuses of an unknown rating and determining their rating by the temperature they were when they failed. Is ...
1
vote
1answer
209 views

What are the dangers of a DIY fuse in a multimeter?

For the past few years I have been running my Fluke 79III without a fuse in it's F44.100A 1kV fuse holder. This has meant that I've been unable to use the 40mA circuit. When I blew the old fuse, I ...