Kevin.
that was an odd question my friend. What benefit do you have of a catastroph
failure photo? Sure, I have all kinds of photo material, but to scan
hundreds of reports to find a particular photo takes time. Instead I go
directly to your question. It depends (Doug TM) on the kind of circuitry
you have. Resistive? Inductive? Current limitation? Lead material? Heat
paths? Lead cross section area? Lead length? etc
Let's compare with a gold bond 1 mil wire. Despite it's thinness, it's
capable of taking 6 amperes DC for some milliseconds. Then imagine a
component lead!! Maybe a hundred amperes instantly. Overcurrent can
appear as a) a inrush current high enough to rise the resistive current so
fast that you melt the lead within milliseconds. The temperature reaches
thousands degrees and the hottest part of the lead vaporises. Typically, it
acts like an explosion. Melt metal spreads around, oxides and soot covers
the surroundings and there is a smell of burnt material. The voltage drops,
some major fuse breaks and nothing more happens. This is the most positive
scenario. What is far more dangerous is if the voltage does not drop (it
can increase instead, inductive load) but continues to feed, arcing can
start and put fire to surrounding components. So, my answer is: if the
overcurrent disintegrates a lead, there will NOT be left a smooth and clean
metal, because that is against all physical laws. With one exception.
Theoretically, if the short circuit current is 'unlimited' and dt/T is
'zero' , the lead may break by electromechanical forces rather than by
thermal causes. The inventors have tried for may years to design fuses that
behave like that. If your leg broke by overcurrent and is still smooth and
clean, hurry , take patent .
My two amperes
Inge
--------------------------------------------------
From: "Glidden, Kevin" <[log in to unmask]>
Sent: den 20 May 2010 19:53
To: <[log in to unmask]>
Subject: [TN] Visual clues of over-current for leads
> Hello,
>
> Can anyone describe or provide photos of what one might expect a lead that
> has been subjected to such a high current that it damaged (burned?
> disintegrated?) the lead?
>
> Would you expect to see charring all the time? Is it possible to see
> smooth, clean surfaces with just a section of the lead missing?
>
>
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