Fuse: fast blown vs slow blown

How dangerous is it to replace a 500mA fast-brown fuse with a 500mA slow-brown one?

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Reply to
Man-wai Chang
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"Man-wai Chang"

** Confucius once say:

" The quick brown fox jumps over the lazy dog "

Think about it ...........

.... Phil

Reply to
Phil Allison

you!

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The danger, on a scale from 1 to 10 is 8. Some equipment can be damaged in a millisecond, so a slow-blown fuse can result in a ruined piece of equipment. For example, an integrated circuit could need 12 volts, but you plug in the wrong wall wart that has no labels on it. It has 18 volts instead of 12 volts, but it uses the same diameter coaxial connector. A fast fuse protects in 400 microseconds, but the slow blow does not blow that fast so the 45 nanometer digital device gets melted in 1000 microseconds.

Reply to
Globemaker

"Globemaker"

The danger, on a scale from 1 to 10 is 8. Some equipment can be damaged in a millisecond, so a slow-blown fuse can result in a ruined piece of equipment. For example, an integrated circuit could need 12 volts, but you plug in the wrong wall wart that has no labels on it. It has 18 volts instead of 12 volts, but it uses the same diameter coaxial connector. A fast fuse protects in 400 microseconds, but the slow blow does not blow that fast so the 45 nanometer digital device gets melted in 1000 microseconds.

** Globemaker is one of those personages who sincerely believes that " Star Trek " is a documentary.

And he has pointy ears too.

Beam me up Scotty ........

... Phil

Reply to
Phil Allison

It depends entirely on the equipment. Slow-blow fuses used to be more expensive than fast-blow fuses, and tend to be less available. So a designer's knee-jerk reaction may be to specify a fast-blow fuse 'because it's there'.

So there's a good chance that you can drop your slow-blow fuse in there and everything will be fine, but if you do and burn something up, don't come crying to me. I would hesitate to do so myself unless I knew what was in the product, and felt that a slow-blow would work OK. I would also hesitate to replace the fuse unless I knew why the original had blown -- fuses blow for reasons, and if the equipment is dorked and blowing fuses, then putting in more fuses will just make it more dorked.

Your best bet is to get the right fuse, and at least try to fix the fault before you turn the equipment on with your shiny new fuse.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

For a multimeter, is it always better to use a fast blow fuse?

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Reply to
Man-wai Chang

Is the 13A BS1362 fuse a fast blow one?

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   @~@   Might, Courage, Vision, SINCERITY.
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Reply to
Man-wai Chang

It depends on the multimeter. I'd stick with the fast blow fuse and stop putting it in 'voltage' mode when you've got it connected to measure current.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

Check to make sure that the fuse isn't being used as the current shunt

-- if it is, then you don't just need the right current rating, you need a matched fuse.

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

It's a glass one, 500mA fast blow according to the manual.

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   @~@   Might, Courage, Vision, SINCERITY.
  / v \  Simplicity is Beauty! May the Force and farces be with you!
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Reply to
Man-wai Chang

Chuckle. If a fuse were used as a current shunt, then when the fuse blows, instead of a few millivolts across the fuse, the meter now gets the full voltage of whatever is being measured. The fuse holder contact resistance will probably be larger than the wire resistance in the fuse (fast blow). I don't think anyone uses a fuse as a current shunt.

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Reply to
Jeff Liebermann

That's the number of the plug, not the fuse:

It does have a fuse inside, but I don't know the value or type.

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Reply to
Jeff Liebermann

That's 'current' mode when you've got it connected to measure voltage, yes?

--Winston

Reply to
Winston

Uhhh...

D'oh!

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Tim Wescott
Wescott Design Services
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Reply to
Tim Wescott

yes

Reply to
Jamie

Hush, you wasn't suppose to notice that! Built in obsolescence.

Jamie

Reply to
Jamie

Too hard to calibrate. :)

I used some test fixtures on the PRC-77 QA line for module interchangability that had to be returned to the cal lab if a module blew a fuse. !@#$%^&*( RCA/NATO design. @#$%^&*

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Reply to
Michael A. Terrell

Hope this helps answer your question!

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John :-#)#

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Reply to
John Robertson

Man-wai Chang Inscribed thus:

No !

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Best Regards:
                          Baron.
Reply to
Baron

"Jeff Liebermann"

** Funny, I have any number of fuses in my bins with "BS 1362" printed on them.
**From the very same Wiki:

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A 13A, BS 1362 fuse is very much a Slow Blow !

.... Phil

Reply to
Phil Allison

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