calculate amp power with fuse size

When we attempt to figure out how much power an amplifier is capable of producing, the first thing we do is look at the number of fuses and the current rating on said fuses. Then we whip out our calculators and begin doing the math. Number of fuses (X) current rating (X) (12, 13.8 or 14.4 volts.) Then multiply that by .6, .7, .8 or .9 depending on the class of amplifier. There is a major flaw in using this equation. Most fuses have 3 ratings that they must comply to in order to be UL approved. The range in which they are rated at are as follows. 100%, 135% and 200%. The fuse at 100% of it's rated capacity will never open. At 135% of it's current rating, it will take no longer than one hour to open. At 200% of it's current handling capacity the fuse should open in under 2 minutes. I know we like to use this to show them how inaccurate the power rating is on their VolfenBahn or AudioHag amplifier, but without an actual ammeter, we are only guessing.  The amp may have 90 amps worth of fuses, but it is probably pulling 120 amps or more on some notes.

http://www.bussmann.com/library/bifs/2017.pdf

The above link is for GMA type fuses, the largest fuse available in that chassis is a 10 amp. It was just the first chart I could find to help explain it. The rating is the same on all types of glass fuses.

Good post.  That always struck my interest.  I have had tech support from a few manufacures tell me that the amps we're installing are drawing way more than the rated fuses on the amps, and now it all makes sense.

And some bigger amps come with no fuses on the amps at all, which would make those calculations very hard to do.  Bottom line I guess would be to purchase your products from reputable manufacture's.