Fuseology or what we should know about fuses

A while back we discussed special cases in electrical systems and defined these as “short” and “open” circuits.  I posed a question about which of these special cases would most likely result in a blown fuse.  The correct answer is that a short circuit will most likely blow a fuse because the current flow in a short circuit tries to go to infinity.  The purpose of the fuse is to limit the current flow by “blowing”, thus preventing excess current from flowing in the circuit.

Fuses come in many styles, types and ratings.  Most of us are aware of fuse amp ratings such as 1 amp, 10 amp, 20 amp, etc.  Although the amp rating of a fuse can be complicated, a simple interpretation would be to say that the amp rating is the current flow above which the fuse will blow.  We will leave it at that for now and talk more about fuse amp ratings in a later article.

A second fuse rating that is important is the voltage rating of the fuse.   Very simply, this is the maximum voltage that can appear in the circuit where the fuse is used.

There are reasons why a circuit designer chooses a particular fuse to use in a circuit.  Because of this you should always replace a blown fuse with another fuse with identical or similar ratings.

Since a blown fuse can occur due to electrical faults in a system, it is important to be able to tell when a fuse is blown.  There are at least three ways to tell when a fuse has blown.  One is to look at the fuse to see if it appears to be blown.  Another way is to check the resistance of the fuse with a multimeter.  A good fuse should read 0 ohms on the lowest resistance range.  A blown fuse will read infinite.  If you are going to check a fuse with an ohm meter, please make certain there is no power in the circuit.  A third method to check for a blown fuse is to use a voltmeter.  This method gets a bit trickier and we will discuss that, and maybe get into meter usage next time.

Until then, happy camping!!