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The fuse can be tested with or without the use of a multimeter. If the fuse is clear, the broken fuse link could be easily seen by the naked eye, unless the fuse is very tiny. Fuses can be tested by swapping, use of light bulbs, and, of course, the use of a multimeter.
When checking a fuse where the contact is visible (such as a glass fuse), you can visually examine it. A metal fuse link is seen very well in glass fuses. You can easily spot if the wire is still attached and if the fuse is still functional.
If you suspect a blown fuse, remove it safely and try inspecting it with a bright light. Sometimes it is hard to see a wire (or link) break due to darkened glass as a result of the fuse bursting.
A break in a 10A fuse is considerably simpler to see than a break in a 250mA fuse. A magnifying glass or even enlarging it on a photograph (if on a phone camera) can help with this endeavor.
Here are the most common ways to test a fuse:
Test #1. Fuse swapping
The safest and simplest approach to test a fuse is to use a multimeter, but if you don’t have one, how do you test a fuse? Very simple! Fuse swapping!
A quick switch of fuses can be an excellent approach to check the integrity of a fuse if you have another portion of the equipment with an identical fuse. This is how you do it:
- Step 1. Take off the faulty fuse from the circuit (and make sure you remember which fuse is which).
- Step 2. Find an identical fuse and determine which circuit it protects.
- Step 3. Remove the known good fuse and exchange it with the fuse (that we think is blown), in the functioning circuit.
If the circuit continues to function with the “possibly faulty” fuse, it is likely that the fuse is in good working order and the fault is somewhere else in the system.
If the previously working circuit fails to function with the fuse, then, the fuse has blown and must be replaced.
** Warning! If you use the good fuse in the questionable circuit, be prepared for that fuse to blow as well.
Test #2. Light bulb
Another interesting (and effective) way of checking a fuse is to put a light bulb to work! An incandescent light bulb with a socket can be used as a rapid stand-in for a multimeter if the voltage of the circuit with the blown fuse is known.
When working on live circuits, make sure you observe all the safety rules and wear the necessary protective equipment. Make sure there is no exposed metal that could create a short circuit or shock you.
- Step 1. Connect one wire to the neutral/common side of the fuse and the other to the line side. If there is enough voltage, the bulb will turn on.
- Step 2. Move the wire from the line side of the fuse to the load side. The light will turn on if the fuse is good. If the bulb fails to illuminate, the fuse has blown and must be replaced.
When you don’t have access to a solenoid type meter, this test is also a fantastic technique to determine if a voltage measurement is for real. Here is another way to make test light when necessary:
If you like to have a bunch of “cool” tools in your road arsenal, just like me, you may want to check out this test light (comes in a digital version as well). It is the easiest way to check a car fuse (for example):
Here are some light testers for you (sold on Amazon, paid link) and they are not expensive at all:
And here is a digital circuit tester from Amazon (paid link). It works just like the light bulb, only it will show you voltage on a digital screen:
Test #3. Continuity Tester
There are many different types of circuit testers out there. Continuity Tester is another easy way to check your fuses for problems. It is a low-cost alternative to multimeters and this is how you use it:
- Step 1. By pressing the metal probe to the corresponding clip on your continuity tester, you can make sure it’s operating. It should light up if it’s working.
- Step 2. To test a fuse, simply contact the probe and clips to the end of the fuse, as you would with a multimeter. The fuse is operating if the tester lights up.
** Important! Before testing, make sure there is NO electricity flowing through the fuse.
This is how you use this continuity tool to check fuses:
Test #4. Multimeter
The best approach for testing fuses is to use a multimeter. The current flow, voltage, and electrical current can all be tested with a multimeter.
Multimeter uses one lead to send a current and the other to measure it. You can measure a fuse’s continuity or ohms to test it. If you have a simple multimeter on hand, here is how you do it:
- Step 1. Connect the red lead to the ohms (Ω) socket and the black lead to the common socket.
- Step 2. Set the dial to Ohms (because we’ll be measuring resistance).
- Step 3. If the metal points are not touching each other, your multimeter should read: “1”. Touch the metal points of your multimeter together to see if it’s working. The reading on your multimeter should be extremely close to zero. Remember this number!
- Step 4. Make sure the fuse doesn’t have any current flowing through it. Connect the metal points to the fuse’s opposing ends (since fuses are not polarized, it doesn’t matter which end of the fuse meets which tip).
If the multimeter reads – 1, your fuse is blown. If it reads the same number as when you touched the metal points, then your fuse is good.
This test is very similar to the Ohms test, only you put your multimeter in the “continuity” setting, instead of Ohms (Ω):
When you touch the metal points of your multimeter together you will hear a beeping sound. The same sound will be when you touch opposing ends of a fuse.
If there is no sound, the fuse is blown.
This article is for informational purposes ONLY and is NOT a replacement for professional advice!