EEVblog 1377 - The Amazing UNPREDICTABILITY of Fuses!

How long does it take for your 400mA multimeter fuse to blow at 600mA?
Grab a chair and watch!
The amazing unpredictability of fusing current ratings at low overloads.
Forum: www.eevblog.com/forum/blog/ee...
Subscribe on Odysee: odysee.com/@eevblog:7
EEVblog Web Site: www.eevblog.com
The 2nd EEVblog Channel: / eevblog2
EEVdiscover: / eevdiscover
Support the EEVblog through Patreon! / eevblog
AliExpress Affiliate: s.click.aliexpress.com/e/c2LRpe8g
Buy anything through that link and Dave gets a commission at no cost to you.
Donate With Bitcoin & Other Crypto Currencies!
www.eevblog.com/crypto-currency/
T-Shirts: teespring.com/stores/eevblog

[@AppliedScience]

Very useful to know! Thanks for doing the tests. I never considered thermal hazard from a near-limit fuse.

[@jkobain]

Dave:

[@toddtempleton6514]

I always keep in mind Murphy's Law of Fuses: A $300 picture tube will protect a 10 cent fuse by blowing first.

[@bumbixp]

Not may channels on KZbin where the audience agrees with: "that would be a fascinating video, tour of a fuse factory". :)

[@jort93z]

That variance is insane. Much more than I expected.

[@westinthewest]

For electrical installations here in the UK, overcurrent is considered separately as overload and fault current. For a multimeter, the usual reason for the fuse blowing is when you forget you're on the current range and you decide to measure the voltage of your car battery. This is when the fuse's I2t rating is important as it must limit that burst of energy before it fries the A/D converter or whatever components are unfortunate enough to be in the way.

[@SlykeThePhoxenix]

You know what they say "Anything's a fuse if you're brave enough".

[@jessicav2031]

I always figured that fuses really are just to protect against shorts and near-shorts. Perhaps similar to a spark gap...only for when things are going really wrong. It seems that the trip tolerance is even worse than I expected!

[@reddev5420]

Kudos for sticking at this Dave! The SIBA was crazy! This video would have blown my mind back in the day when I thought a 300mA fuse would blow the instant the current reached 301mA. :D

[@curtwuollet2912]

In power electronics, a blown fuse usually means an active device has shorted to protect the fuse.

[@lazyjackass77]

Not enough smoke was produced during the making of this video.

[@mikeselectricstuff]

That Siba was marked FF - this would be faster than normal fast blow (Frickin' Fast ?)

[@vinayakjadhav1719]

Wife: What are you doing ?

[@MarcoTedaldi]

An older electronics engineer once told me more or less that lesson:"the only thing defined about a fuse is, that it should not blow at rated current"...

[@williamsquires3070]

It’s one of those new Schrodinger’s quantum fuses; they’re both blown and not blown at the same time. It’s not until you measure it on the continuity/diode-test range on your meter that you know for sure. 😉

[@FalkBay]

I've seen many fuse holders on PV installations melted because of the heat that they dissipate. Thank you for this valuable information.

[@McTroyd]

Open an online casino! EE nerds place their bets on when the fuse will blow. Huge money maker right there! 🤑🤓🤣

[@sternis1]

Very useful information! I've done some work with fuses in appliances, but I've never thought about this. Thank you!

[@Fix_It_Again_Tony]

Fuses were one of the biggest eye-openers when my team started to develop intrinsically safe hardware for explosive atmospheres. The standard (IEC 60079-11) automatically assumes 1.7x the rated current can flow continuously. Then, if you want your fuse to be used as a current limiting device on which safety depends you need to multiply the I_rated * 1.7 figure by an additional factor of 1.5. So the current assumed to flow through the fuse continuously is I_rated * 1.7 * 1.5. For a 400 mA fuse this is 1.02 A. It can make it really hard to meet the power derating requirements of all the downstream components when 2.55 times the rated current can flow. No parts can be run at higher then 2/3 the rated power if safety depends on that component.

[@arielbriner]

Thanks for investing the time on this one Dave. Finally I have something to point clients to when trying to explain why designing fusing strategies is so hard!