Fuse Voltage Ratings

Everyone knows what the amperage rating on a fuse is for and what it means. But do you know what the voltage rating is for? Maybe not what you think.

Quite a few people think that the voltage rating of a fuse indicates the voltage that the fuse will blow (or break) at, like what the amperage rating specifies.  In fact, the opposite is true.

The voltage rating of a fuse is its “arc over” rating, or how much voltage a blown fuse can withstand without an arc forming between both ends of the fuse.  If an arc forms it would effectively bypass the blown fuse, reapplying power to whatever circuit the blown fuse was trying to protect.

Because of this, you want to make sure that the voltage rating of a fuse exceeds the normal voltage it will be operating under.  This is obviously different than how you select the amperage rating of the fuse, where you want a rating that is as close as you can get to the normal operating demands of the circuit it is protecting.  Without going under, of course.

For example, if you have a 200v circuit that pulls a max of 2.7 amps, a 3 amp @ 250v fuse might be appropriate, while a 3 amp @ 200v fuse would not be.