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 ...

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27
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\$ ...
25
votes
4answers
2k views

Can thin sections of copper traces be used as fuses?

Is it safe to use thin sections of copper traces as one-shot fuses when cost is important, but when it is also vital to protect the rest of the circuitry? Should the solder mask be removed at that ...
21
votes
5answers
19k 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 ...
18
votes
5answers
33k 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. ...
16
votes
4answers
4k views

Why did my fuse blow after 3+ years of no problems?

For several years, I have had a solenoid wired to the 24VDC output of a PLC (Rockewell Automation 1769-OB16). To protect the PLC output card, a fast-acting 500mA fuse was installed between the PLC ...
13
votes
6answers
84k 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 ...
11
votes
6answers
2k views

How To Know If a Fuse Will Work Properly?

I want to know what kind of periodic test we use to test if a current-limiting fuse will normaly open and protect an electronic circuit (a battery charger) if a failure occur (short circuit or over ...
10
votes
4answers
8k 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 ...
10
votes
2answers
279 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 ...
10
votes
1answer
837 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 ...
9
votes
4answers
4k 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 ...
8
votes
4answers
3k 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
5answers
50k 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 ...
8
votes
3answers
570 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
522 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
4answers
1k views

Why aren't high-current ammeters protected with a fuse

Why is it that the low-current range on an ammeter (200mA) is fused and not the 20A range? I recently lost a multimeter because I connected the ammeter in parallel with a power source by mistake. ...
7
votes
2answers
1k 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 its 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 ...
7
votes
6answers
24k 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 ...
7
votes
3answers
3k 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. ...
7
votes
3answers
4k 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 ...
7
votes
1answer
2k 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 ...
7
votes
3answers
9k 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 ...
7
votes
2answers
13k 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 ...
6
votes
8answers
1k views

Can I use a 10A light switch with an appliance with a 13A fuse?

I have a vacuum cleaner, which I wish to add a switch to, so that I can leave it plugged in all the time and use the switch to turn it on and off. The vacuum cleaner has a fuse rated 13 Amps. I ...
6
votes
2answers
1k views

Short circuit protection for high current wearable: fuse, polyswitch, TBU, circuit breaker, something else?

I am thinking about design elements for a rather high current, battery powered, wearable application. Maximum current of 40A at 5V, but typically around a third to a half of that. Power would come ...
6
votes
1answer
676 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
229 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
4answers
8k 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 ...
5
votes
5answers
2k 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
3answers
415 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 ...
5
votes
3answers
4k 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 ...
5
votes
3answers
348 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 ...
5
votes
1answer
206 views

Why can't I blow a fuse?

In the book I am reading, there is an experiment that consists of connecting an automotive style fuse and a 1.5V battery to observe blowing of a fuse. However my fuse does not blow. I have repeated ...
5
votes
3answers
1k 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
1answer
68 views

How does a fuse affect creepage reqirements?

I am designing a mains-powered device that has to comply with IEC 60079-15 (Non-incedive industrial eqipment). Creepage distances in this standard are inherited from IEC 60664, pollution degree 3. For ...
5
votes
3answers
274 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
4answers
981 views

How can I detect fuse failure?

I have two components in parallel on a DC circuit driven by a single momentary switch. Each component is individually fused. I need to detect failure of either fuse and in that event power on a ...
4
votes
5answers
734 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 ...
4
votes
2answers
622 views

Did I choose the correct fuse for my USB powered circuit?

I need to drive a circuit (operational current 150mA) with a USB port. I would like to protect the port with a fuse and from this question I concluded, that what I want is a PTC fuse. Is that the ...
4
votes
1answer
2k 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
2answers
601 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
2answers
398 views

Current Determination - 12V to 5V (USB Output)

I am attempting to determine the current in an automotive installation of a 12V to 5V converter that will supply a USB output. Max output on the 5V side will be 3 Amps. ...
3
votes
2answers
476 views

Filtering Capacitors before the fuse or after the fuse while limiting inrush current?

There are basically two questions I have for this circuit. 1) Which capacitor configuration is good? before fuse or after fuse 2) How do I limit my inrush current? My thoughts: I am confused ...
3
votes
2answers
509 views

Are regular fuses temperature sensitive?

Are common fuses, like AT car fuses, temperature sensitive? Say a 12v 5A fast blow fuse, would it have any significant change in its reaction at 0ºF than it would at 100ºF? In either time to blow or ...
3
votes
4answers
2k 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
3k 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
358 views

What is this Externally-Triggered Fuse?

In the datasheet for an overvoltage protector (TI BQ771815) there is a device I don't recognize: It is used in the datasheet as a fuse which can be opened by an external signal from the overvoltage ...
3
votes
1answer
204 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
3answers
3k 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
3answers
165 views

Is this the proper way to fuse a DC/DC Converter?

I am designing a solar power system for camping. I'll use a couple different DC/DC converters to provide DC voltages for the specific items I want to power. I want to properly fuse the various ...