> -----Original Message----- > From: Kai Keskinen [mailto:kalevi@xxxxxxxxxx] > Sent: Thursday, 26 August 2004 10:42 > To: Mark.Hofmann@xxxxxxxxxxxxxxx; a.ingraham@xxxxxxxx; 'Si-List' > Subject: [SI-LIST] Re: Can a thin PCB trace be used as a reliable fuse >=20 > Yes, you can use a thin trace as fuse. How do you fix the thing when the > "fuse" goes? Do you build a new pcb and populate it again? The whole poin= t > of a fuse is that you change the fuse if there is a fault. You don't thro= w > away the PCB. >=20 > Cheers, >=20 There are a range of applications where SMT or through-hole fuses are used = (i.e. not the easily replaceable socketed fuses). As pointed out by Bren= t, they may be used because of their low cost or special characteristics = and they are usually the last line of defence, protecting against some ca= tastrophic event which very rarely occurs but can't be ignored, such as s= afety or fire hazard concerns. These days, the cost of the service technician just touching the board woul= d be prohibitive because of the overheads involved, so usually the board = or the whole box just gets replaced. Who would want to repair something = that costs, say, $25 when new? Out with the old, in with the new! Besid= es, an event serious enough to blow the fuse, may have already caused oth= er, not immediately obvious problems. You don't want that board coming b= ack in 3 weeks for yet another repair! Sometimes non-repairable fuses can be found on telco grade interface boards= . Among other things, these fuses may protect from a short between the t= ransmission cable and power lines. Now, how often does that occur??! St= ill, as different cabling might meet in e.g. service tunnels, one does wa= nt some protection and regulations may require it, accordingly. =20 The bulky, easily replaceable fuses sometimes may not be practical or simpl= y can't be used. So when that proverbial lightning strikes, the user is = probably not too surprised to hear that his/her interface card is toast b= ut you still want to be sure that that's all that goes in their system, s= o you throw in a small, non-repairable fuse or two... Cheers, Sandor ------ Sandor Daranyi Snr Design Engineer ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu