Brymen BM867s: Fuse contradiction

[mcc]

Hi,

( I am no native speaker -- sorry for any confusion my wods may spend...it is not intended

this is my first posting to this forum.
I want say a BIG THANK YOU to Dave for all the very informative videos
and for makeing the way he make the videos! Great stuff! Thumbs up!

I have a Brymen BM867s (no "T" before "BM"). On the front between the COM jack
and the mA/uA it says: "MAX 0.6A, HBC fused".
The manual says "0.44A HBC FUSE" for that.

0.6 A makes sense to me ... due to the 50000 counts.
0.44 A make lesser sense regarding this.
Normally I would think: 0.6A to a 0.44A fuse would blow it up.

What is wrong (and why it is so nevertheless):
The printing on the meter or
the printing on in the manual?

Thanks a lot for any help in advance!
Cheers
mcc

[IanB]

I think nothing is wrong. It takes a very large over current through a fuse to break it. Passing 0.6 A through a 0.44 A fuse for short periods will be fine.

[mcc]

I think nothing is wrong. It takes a very large over current through a fuse to break it. Passing 0.6 A through a 0.44 A fuse for short periods will be fine.

Hi Ian,

thanks a lot for the information!
How long is "a short period of time"?

Cheers
mcc

[Hydrawerk]

Find a datasheet of a HRC fuse.

[wraper]

At room temperature, fuses usually need almost two times of the rated current to blow at all. At lower currents they will hold infinitely.

[mcc]

Find a datasheet of a HRC fuse.

Did this before. 0.6A is not specified...

Cheers
mcc

[Hydrawerk]

See this SIBA  5021006.0,44.
http://www.download.siba.de/pdf/artikel/5021006.pdf

[mcc]

At room temperature, fuses usually need almost two times of the rated current to blow at all. At lower currents they will hold infinitely.

..that is: At room temperature a fuse does not blow at all when 0.6A is applied?
Isn't that in contradiction to for they are build for: Protecting against overload... ?

Only my two cents...your multimeter may vary ...

Cheers
mcc

[Hydrawerk]

This graph says it clearly. http://www.littelfuse.com/~/media/electrical/datasheets/fuses/industrial-and-ul-fuses/littelfuse_fuse_flu_datasheet.pdf

[mcc]

See this SIBA  5021006.0,44.
http://www.download.siba.de/pdf/artikel/5021006.pdf

Ok, that is more specific...had a BUSSMAN datasheet before.
Nonetheless for me it is a contradiction, that a 0.44A fuse will blow after
three years when 0.6A are applied.
Electronics are faster than this, I thnk....

Cheers
mcc

[mcc]

This graph says it clearly. http://www.littelfuse.com/~/media/electrical/datasheets/fuses/industrial-and-ul-fuses/littelfuse_fuse_flu_datasheet.pdf

Ok...seems something like 'more than 1000secs'...
Logarthmic scaling make estimations beyond paper sheet edges
a little diffcult...

Cheers
mcc

[SeanB]

0.44A means the fuse will survive this forever in the operating temperature range. Thus if you drop below the maximum temperature by a large amount ( a lot of fuses are specced at 70C, as many of them are used in enclosures that will run at this internally from generated heat from curreent flow) then they can carry a higher current before the heating inside causes it to melt.

As well there is variation in thickness of the wire or strip used, and this, along with slight changes in the alloy composition either in the batch or from batch to batch, gives this range. Remember the function of a fuse is to protect the cable, and to prevent fires from overcurrent, in most if not all cases they are not going to protect electronics. The fuse has to fail before the cable, so if the cable will handle the current for x minuted before melting the insulation, the fuse just has to blow before that time.