Stephen
I think I wasn't making myself clear here. The voltage I was referring to was the voltage across the fuse itself (i.e. the differential voltage between one end and the other). This is a function of the internal resistance of the fuse compared with the resistance of the rest of the circuit, and the voltage across the whole circuit.
If (say) the fuse has a 1 ohm internal resistance and the rest of the circuit has a 99 ohm resistance, the total being 100 ohms, then 100 volts applied across the circuit produces a current of 1 amp through the whole circuit, including the fuse. But the fuse has a resistance of 1 ohm and is carrying 1 amp, so the voltage across the fuse (between one end and the other) is 1 volt. So should this fuse therefore be rated at 1 volt or 100 volts? Does it matter?!
The current rating of a fuse depends on its internal resistance and the difference in voltage at its two ends. These are what determine both the current it is passing (V/R), and the power it is dissipating (V^2/R or VI). But the 'V' in these expressions is the voltage across the fuse rather than the voltage in the rest of the circuit.
Cheers,
Andy
--------------------------------------- Andy Nicholl Dunfermline, Scotland Fax 0870 130 4955 email [EMAIL PROTECTED] ----------------------------------------
-----Original Message----- From: Duo/2400 List [mailto:[EMAIL PROTECTED] On Behalf Of Stephen Sent: 07 January 2004 18:25 To: Duo/2400 List Subject: [Duo2400] Re: 2400 fuse
??? The voltage rating of a fuse is VERY important. I don't know how much damaged Marine electronic gear I've seen over the years where someone used a 120v fuse instead of a 12v fuse of the same amperage. P = VI, power equals volts times amps.
Stephen
Hi!
There would not normally be a voltage rating for a fuse, because they work on the amount of current passed, not the voltage. 5 amps at 1 volt is the same as 5 amps at 110 volts as far as a fuse is concerned.
A fuse has a very low resistance, and works (blows) only on the basis of the differential voltage between the two ends, not the absolute voltage. I=V/R if I remember correctly.
There may of course be other considerations, such as size or rate of blow, but a voltage rating will normally only refer to the amount of insulation in the construction of the fuse, etc., which prevents arcing
over to other nearby components.
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