| Electronics > Beginners |
| 10A Fuse on Multimeter |
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| skillz21:
Ok, it makes so much more sense now ;D the 600v is for after it blows, got it! One question, how does it actually know when its 10A? Doesn't the heat produced depend on the wattage? |
| wraper:
Voltage rating has nothing to do with when fuse will blow or how much power it will dissipate. All that matters is current rating. Voltage rating on the other hand shows what max voltage it is guaranteed to interrupt. If actual voltage is higher than fuse rating, it may start to arc instead of interrupting current flow. |
| cowana:
The fuse will have a certain resistance, say for example 0.05 ohms. When there is 10A passing through it, this will create a specific voltage drop (0.05 * 10 = 0.5V in this case). That equates to 5W dissipation in the element, which melts it. The fuse doesn't care that it was in line of a 12V rail (or whatever it is) - the power dissipation in the element just depends on the voltage drop across the fuse. |
| Adam60:
Your meter is probably rated CAT III and part of that rating system is explained vefy well above. Google ABCs of multimeter safety by Fluke and you can read about the different categories and their specifications. I believe there are currently 4 of them |
| Nerull:
--- Quote from: skillz21 on January 08, 2019, 09:24:39 pm ---Ok, it makes so much more sense now ;D the 600v is for after it blows, got it! One question, how does it actually know when its 10A? Doesn't the heat produced depend on the wattage? --- End quote --- Ohms law. The fuse has a fixed resistance (well, its probably not actually fixed, but we'll pretend it is). Since resistance is fixed, 10A will always result in the same power. P=I^2 * R. If a fuse requires 1W to blow and has a resistance of 0.1 ohms, than we can calculate that the fuse will blow at I = sqrt(P/R) = sqrt(10) = 3.1A. Thus we would rate that as a 3.1A fuse. The voltage throughout the rest of the device is completely irrelevant to the voltage across the fuse. At 10A a fuse will always drop a given voltage and dissipate a given power depending only on its resistance, no matter what voltages exist elsewhere. |
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