Rich, If the fuse is properly selected it will not open until the equipment fails. In that case the unit needs to be repaired anyway. I learned the hard way to select fuses to open under true fault conditions and not nuisance open.
Dave Cuthbert Micron Technology From: [email protected] [mailto:[email protected]] On Behalf Of Richard Nute Sent: Thursday, March 11, 2004 12:53 PM To: Stone, Richard Cc: peter merguerian; [email protected] Subject: Re: Wide Voltage Range ITE Product with a 250 V 3.0 / 3.15 A fuse Hi Richard: > why cant the 3 amp only be marked? > its the lower current rating > thus best protective of a product, 1. A 3-amp fuse is not readily available outside North America. Most people want to replace a fuse NOW, and not wait for a special order. If a 3.15-amp fuse provides equal protection, then a marking indicating both ratings satisfies users through- out the world. 2. A lower current rating does not necessarily provide the best protection. The fuse rating is selected on the basis of the consequences of a fault condition. For fault currents below the fuse rating (yet more than the input rating), other safeguards must provide protection against fire or whatever other hazards may exist. The fuse is a safeguard only for fault currents exceeding the fuse rating. An excessively low current fuse may operate on normal current spikes, and thus be a nuisance by requiring frequent replacement. This may prompt the user to replace the fuse with one of a higher rating, which in turn may compromise the safety of the product. > many labels of ratings for equipment > state 110/220, yet, you only see the lower > voltage's ( 110)'s current(higher) rating on the product, > please educate me why this fuse situation > is more critical/important than a units overall current > marking stamped on the power ratings. The input current rating is a normal- condition current. The fuse rating is selected to limit the maximum fault- condition current. The input current rating of the product is used to choose the current ratings of many primary-circuit components such as appliance couplers, switches, wire size, power cord size, etc. It also gives the user an idea of the load on his mains distribution system. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
