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. > --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.557 / Virus Database: 349 - Release Date: 30/12/2003 ---------- Duo/2400 List, The friendliest place on the Net! A listserv for users and fans of Mac subportables. FAQ at <http://www.themacintoshguy.com/lists/DuoListFAQ.shtml> Be sure to visit Mac2400! <http://www.sineware.com/mac2400> To unsubscribe, E-mail to: <[EMAIL PROTECTED]> To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]> Need help from a real person? Try. <[EMAIL PROTECTED]> ---------- Dr. Bott | 10/100 Ethernet for your 2400 is finally here! MPC-100 | <http://www.drbott.com/prod/mpc100.html> RoadTools $30 PodiumPad available at Apple retail stores, $20 Traveler CoolPad at Staples. Both in white for iBooks at <http://roadtools.com> Midwest Mac Parts ][ <http://www.midwestmac.com> After-market parts for Macs. ][ 888-356-1104 ][ MacResQ Specials: LaCie SCSI CDR From $99! PowerBook 3400/200 Only $879! Norton AntiVirus 6 Only $19! We Stock PARTS! <http://www.macresq.com>
