Why cant you use a 250 volt fuse on a 480 volt circuit?

The main reason why is that it would be very deceptive to consumers. For example. a 120v circuit that draws one amp; might be able to be converted to 240v that would only draw 1/2 amp. At 480v, that same circuit would only draw 1/4 amp, so you would need to be able to figure out what amperage you need at 480v. Now there is also more to understand with this. A 480v ac system consists of three phases, the most common is 3 phases of 277v. If you measured one phase to ground you would read 277, if you measured phase to phase, you would read 480v. There are also other varaitions including 240v to ground and 480 phase to phase. Depending on the tap off of the transformer you might actually be able to use a 250v fuse on each phase. Since each phase is fused separately, I can guarantee you will never find one that reads 480v to ground. If none of this makes sense, than you should go to the store and purchase the 480v fuse, or call an electrician.

Fuses have a small connecting link in them that melts in response to the current. Ratings below 32 volts can use almost any type of metal link in air, and it will safely interrupt the circuit. As the voltage rating goes higher, special exotic properties of metals and filler materials have to be used to safely stop the current. If the fuses does not have the correct properties to stop the current arc, the fuse can explode or become a conductor feeding a short circuit! This could cause switchboard failure or personnal inuries.