Article
If you work with electrical processes or electronics, fuses are 
obviously a part of your life. While circuit breakers are used for many 
applications, the good old fusible link in its various forms and 
iterations is still a necessary part of many circuits.<br><br>Fuses come
 in different shapes, sizes, and functions. When choosing a fuse for a 
circuit, choose carefully. The characteristics vary widely, and you need
 to use the one for the application you're designing.

Fuses – The Weakest Link is Often Your Strongest Link

Steve Maurer, IME
If you work with electrical processes or electronics, fuses are obviously a part of your life. While circuit breakers are used for many applications, the good old fusible link in its various forms and iterations is still a necessary part of many circuits.

Fuses come in different shapes, sizes, and functions. When choosing a fuse for a circuit, choose carefully. The characteristics vary widely, and you need to use the one for the application you're designing.

And that goes double when replacing a blown one. You might be tempted to use just any old fuse, particularly if an exact replacement isn't readily available.

Not. Good.

Finally, before we get into fuse types and their uses, I want to address a somewhat funny, but entirely serious issue. Before you change the fuse, troubleshoot the system to discover why it failed in the first place. Of course, the obvious reason is to prevent a repeat performance.

If there's a problem with a component or system, it needs corrected. And I highly recommend you don't perform the old "smoke test" to troubleshoot. I've seen alleged troubleshooters use increasingly higher-amp fuses to pinpoint the issue. They think that by "letting the smoke out," they're saving time.

That is amateurish and can lead to safety issues as well as expensive machine or system damage.
Now you might find nothing wrong, and that's entirely possible. Nothing lasts forever and that includes fuses. Just like an incandescent light bulb, fuses can burn out. They might fail for various reasons, including heat buildup, continuous high voltage drops and other factors.

Remember, fuses are calibrated devices, "tuned" to fail at a certain amperage. Particularly for time-delay fuses on motor circuits, they can be subjected to inrush amperages at start up. The more often they're stressed, the sooner they'll fail.

So, before you change that fuse, make sure you understand why you're replacing it.
The weakest link in your overcurrent protection plan … could be your strongest link for safety.

Why Do We Need Overcurrent Protection Anyway?
Overcurrent states happen on every electrical system eventually. No matter how well-designed, all will experience them. The overcurrent, even if moderate, can do some real damage if not removed quickly.

System components overheat and fry. Insulation melts or vaporizes. Conductors, contactors, and other components can literally go up in smoke. And the fires, explosions, and poisonous fumes can cause people to panic and even injure them. Deaths from these conditions are a real possibility.

Of course, the National Electrical Code, OSHA, UL, and other regulatory bodies have rules and standards in place to keep the potential for injury and damage down. But you must design systems that are properly protected … and ensure the fuses used meet the codes and standards.

Use the Right Fuse
Because systems and even types of overloads vary, it's necessary to use the correct fuse type and class for the application. On motor and drive circuits, you probably need a time-delay fuse. This handles some overload in the circuit, caused by inrush.

Other circuits need a fast-acting fuse. This protects sensitive electronic components that may be damaged quickly by an overload condition.

Check with UL and NEC® information and guidance if designing a circuit. And if you're troubleshooting or making repairs, use a direct replacement. Some newer technology fuses may be possible for that. Often, they're designed for even better protection than the original. Some fuses have indicators that change color when the fuse is blown. This can significantly cut down on time spent troubleshooting.
And remember that the fuse holders are just as important. Many are designed to be "finger safe." And for some applications, they are built to reject fuses that aren't the correct type. Don't force the incorrect fuse because the potential for damage increases if you do.

In any event, make sure you're using the correct fuse. The weakest link in the circuit is also your strongest link for the safety of your device, your property … and your people.
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