Fuses and How They Work

A Simple Explanation

Each electrical component, whether its a motor, light bulb, toaster, etc., draws so much power when it runs.  The mfg's label each appliance to tell people and technicians how much that particular appliance draws. 

For example, if you have a, a microwave and a toaster.  The microwave draws 8.9 amps and the toaster 5 amps.  That would come to 9.4 amps.  The circuit that they are connect to needs to be large enough to carry that load with no problem.  The typical goal is 80% of circuit capacity so if you are drawing 9.4 amps and that's supposed to be 80% of the total circuits ability, you would go up to the next size fuze or breaker to handle that circuit.  The next common size is a 15 amp breaker which uses #14 wire.  You could have a few receptacles and lights on this circuit also.

Wire is also 'sized' and capable of carrying so much juice.  Some wire is solid, some stranded.  Each has a particular rating. 

Fuses, put simply, are small pieces of wire that are capable of carrying so much electricity.  If you try to use an appliance that is rated for more than the fuse, the wire in the fuse will burn in two, opening the circuit.  The smaller fuse, the smaller the wire or metal strip.  The larger, likewise, the larger the wire or strip.

Fuses don't just 'get old' or anything of the sort unless there is water damage and the element is rusted and/or corroding such as in extremely moist applications.  If a fuse blows, there is or was a problem in the circuit.  Some attention needs to be paid to the appliance to determine the problem.  If not resolved it'll keep doing it over and over.

Often times we find bad connections in electrical panels, control panels and the like.  If you loosen a lug on the breaker in your electric panel, you'll find that it will run hotter, heating up the line from there to the appliance.  The appliance, not knowing whats going on keeps drawing the power it needs to run.  The same thing that happens when a fuse blows, the weakest link burns in two.  In the meantime, everything downstream, the windings, the wire, the controls all get hot.  Over time, it will ruin each component and/or burn up.

If circuits are not sized correctly, when things do 'burn up', they won't blow the fuse.  If you've got a 60 amp fuse where a 30 amp should be, there's gonna be some fire flying before the fuse blows.  Sort of like arc welding.  Its not good.

Air Conditioners are a good example of this.  If a unit requires a 40 amp fuse and they have a 60 amp breaker on the circuit with a 60 amp fuse, there's gonna be some fire and additional equipment damage.  It more than likely will stay contained, but the additional damage to the unit is unnecessary and considerable.

Make sure your circuits are fused correctly and of appropriate size.

The label on the outside of each unit, refrigerator, etc., will tell you what that particular applance should draw.  Make sure the fuse size and breaker size are the same for individual circuits such as an air conditioner where there is nothing else on the circuit but that.

Got questions?  Keep it brief but ask away.  E-mail me from the main page.