Resistors tend to have a DeltaR/R specification and they define the conditions under which the DeltaR/R characteristic is met. For example http://www.vishay.com/docs/20035/dcrcwe3.pdf Some specifications such as power dissipation include a DeltaR/R requirement. It is often the DeltaR/R that determines the power dissipation for a size of resistor for a given manufacturer. If you actually want to fuse the resistor then I think that is probably a minefield, and you are on your own................... :-) Regards Rex Rex Waygood Technical Manager Hansatech EMS provides value manufacturing through engineering and quality Hansatech EMS Limited Benson Road Nuffield Industrial Estate Poole Dorset BH17 0RY +44 (0)1202 338200 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair Hogg Sent: 02 December 2010 20:39 To: [log in to unmask] Subject: [TN] [Somewhat NTC] When does a resistor become a fuse? This is a little off the normal Technet topic genre, but I was wondering if anyone out there may have some data on how long a resistor can withstand overcurrent before it changes resistance / fuses open? I'm taling about a standard 0805 carbon film resistor, for example 100 ohms: at 1 mA it drops 100 mV and dissipates 100 uW, no big deal for a 125 mW device at 10 mA it drops 1 V and dissipates 10 mW, still no big deal at 100 mA it drops 10 V and dissipates 1 W, until the resistance increases dramatically How much of a time duration can the device withstand at 100 mA? Is there a correlation between overload and time? The graph in http://www.koaspeer.com/pdfs/Thick_Film_Pulse_Limitation.pdf seems to indicate that an 0805 (2A on the graph) can dissipate 1.5 W for 1 second. Does this make sense? Thanks, Blair --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------