Bad fuse that looks OK

[dogememe]

I was reading a post on the forum where someone mentioned fuses can be bad without looking bad.

I am sure it’s technically possible but I’m curious if anyone has actually first hand experienced this? Where a fuse does not look bad (not burnt, filament not broken, etc) but was not good when tested with a meter and/or replaced.

Look forward to your replies.

 

[Ausfahrt]

I have experienced this but it only takes a few seconds to check the resistance with a meter.

 

[SHOZ]

I've seen it too . Usually some discoloration on the actual fuse material.

 

[ls1mike]

See it all the time on Submarines. This is a thing. I always put a meter on them.

 

[Chris142]

Was pretty common on the old glass fuses. They would open inside the metal end where you can't see it.

 

[E150GT]

Older german fuses would corrode on the tips and not work. The fuse was still good but you had to twist them or remove them to clean the tips off. It was always good practice to rotate them every so often.

 

[tessaseveride]

I see it sometimes on automotive fuses. The fuse will even pass continuity tests. It just won't carry a load without substantial voltage drop.

 

[ragtoplvr]

Yes, I have seen this on both the old glass type and the newer blade type

Rod

 

[Dave Sherman]

My dad's 1976 Grumman Tiger (light plane) went through a rash of fuses failing, but not because they burned out. Our reasoning was age and years of vibration took their toll and the thin metal fuse just cracked internally.

 

[Lubener]

Only way to check a fuse is with a meter. Visually doesn't always work.

 

[X15]

I see it sometimes on automotive fuses. The fuse will even pass continuity tests. It just won't carry a load without substantial voltage drop.

Checking voltage drop is key, static resistance tests only tell you so much.

Blade type fuses often have small little exposed squares of metal on the top that you can touch multimeter probes to and check for voltage drop. Usually it should be a small amount of millivolts, if you see the full battery voltage that means the fuse is open.

 

[tessaseveride]

Checking voltage drop is key, static resistance tests only tell you so much.

Blade type fuses often have small little exposed squares of metal on the top that you can touch multimeter probes to and check for voltage drop. Usually it should be a small amount of millivolts, if you see the full battery voltage that means the fuse is open.

Right. That's what I'm saying. I used to check continuity all the time because that's what I was taught. Got burned on too many fuses that would show continuity, but wouldn't carry a load. I've changed my process since.

 

[X15]

Right. That's what I'm saying. I used to check continuity all the time because that's what I was taught. Got burned on too many fuses that would show continuity, but wouldn't carry a load. I've changed my process since.

Yes, I too had to learn the hard way!

it's especially important when checking relays:

Identifying Suspected Relay Failures

Read guidance from TE engineers about how to identify and verify possible issues with relay performance.

www.te.com

 

[mrbreezeet1]

That's how's comes you always check for power on both sides of a fuse under the conditions it's supposed to have power.
You don't just look at a fuse and say it's good!
Or just replace it with a new fuse and say it's good~!!

 

[Elkins45]

I went crazy trying to figure out why my lighter wasn’t working. The fuse looked good and had continuity. Finally I just put in a new fuse anyway and that fixed it.

 

[4329]

I was reading a post on the forum where someone mentioned fuses can be bad without looking bad.

I am sure it’s technically possible but I’m curious if anyone has actually first hand experienced this? Where a fuse does not look bad (not burnt, filament not broken, etc) but was not good when tested with a meter and/or replaced.

Look forward to your replies.

Had a few customers trying to convince me that their fuses where ok based on appearance, every time they where wrong. Check with a test light as this will put a small load on the fuse unlike a multimeter that will not load the circuit.

 

[mrbreezeet1]

I went crazy trying to figure out why my lighter wasn’t working. The fuse looked good and had continuity. Finally, I just put in a new fuse anyway and that fixed it.

Yeah, couldn't handle the load. As mentioned above, sometimes we need a load on any circuit when testing. But FWIW a 12 V test/pick light is a better load than a DVOM.

 

[mrbreezeet1]

Had a few customers trying to convince me that their fuses where ok based on appearance, every time they where wrong. Check with a test light as this will put a small load on the fuse unlike a multimeter that will not load the circuit.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
THIS {I see I am late to the party as usual }

Yeah, couldn't handle the load. As mentioned above, sometimes we need a load on any circuit when testing. But FWIW a 12 V test/pick light is a better load than a DVOM.

 

[mrbreezeet1]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Yeah, I give big important information, meanwhile someone else already said it, I just don't read the whole thread before I run my jibber jabber.

 

[oil pan 4]

I was reading a post on the forum where someone mentioned fuses can be bad without looking bad.

I am sure it’s technically possible but I’m curious if anyone has actually first hand experienced this? Where a fuse does not look bad (not burnt, filament not broken, etc) but was not good when tested with a meter and/or replaced.

Look forward to your replies.

I had a fuse where the fuse wire was just broken, not burnt out. It was in use when it failed. I'm guessing I turned the car off, everything was working fine and while the car was off and there was no current flow the fuse wire broke after it cooled down.