Just because you have a filter rated 6A, it does not mean you need to protect it with a 6A or smaller fuse. With regard to ITE standards, if your product passes safety tests without a fuse, relying only on branch circuit protection, you are not required to have a fuse in the product. If your product fails safety testing with only branch circuit protection, and a smaller fuse is needed to provide safety, then that fuse becomes required for safety reasons. It is also important to choose and label fuse sizes appropriate to the country of use, for example IEC fuses internationally, and UL/CSA fuses in North America. This applies to fuse size, rating and time curves. The fuse size has nothing to do with the rating of the product. Fuse sizes come in standard increments. If you have a product which will not run reliably at a standard fuse size which provides safety, you have a design problem which needs to be solved. Note that a 5A fuse does not blow at 5 amps. It blows at a higher current. How high and how quick depends on fuse curves available from the manufacturers. IEC fuses typically blow at currents closer to their ratings than US fuses.
Sometimes you will choose a high value fuse, for example a 10 amp fuse on a 2 amp product, in order to improve reliability. The fuse can blow and prevent fires if the power supply fails, but not blow due power surges, startup transients, etc. Sometimes you will choose a fuse very close to the actual product consumption, for example in order to protect against burnout during brownouts, realizing that fuse replacement may be frequent but product repair costs will be kept low. Sometimes designers will use two fuses, one larger one internally and not replaceable, since users frequently pay little attention to correct fusing and will upsize during replacement. Bob [email protected] wrote: > Group, > > I have an interesting problem with a mains filter and fuse. We have a > product with a 6 amp filter that can draw up to a maximum of about 5.8A. The > filter has a built in 20mm fuse holder and we would normally fit a T type HBC > fuse. > > The problem is that all fuses appear to be available in prefered values, the > nearest of which being 5 (too small) or 6.3 (too large) > > I'm sure that this is not the first time someone has encountered this so your > comments would be appreciated. Ideally we are looking for a 20mm 6AT HBC fuse > with european and UL approval or recognition. Does anyone know where I can > obtain such a fuse? > > Many thanks is advance, > > Duncan Hobbs. > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Jim Bacher: [email protected] > Michael Garretson: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
