On Nov 26, 15:45, John Allain wrote: 3AG means "Automobile Glass size 3". I suspect those designations have more to do with heating, rupturing, voltage, overload capacity, and most especially materials, shape, and dimensions, than with "slow" or "fast". Maybe, but how much is "slightly"? The slow-blow was probably intended to cope with short-duration inrush current, but reliably blow if the current was too high for more than perhaps a few seconds. A "fast" fuse will typically blow at 250% - 350% of the nominal value within 1-2 seconds, but a "very fast" fuse might blow within 0.2 seconds. I've seen some "very fast" fuses described as blowing at 1000% current within 0.001 seconds. That's only 10 times nominal current rating, so it wouldn't allow for much of an inrush current! As far as I know (and I am not an expert, just someone who is sad enough to read lots of catalogues), the difference between slow/medium/fast/very fast is primarily tolerance to short-duration overloads like that, ie like inrush current. Nope, see above. Fuses aren't expensive. I'd try to find the right one. -- Pete Peter Turnbull Network Manager University of York