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#130247 - 02/27/06 02:36 PM Under the hood of melting wires  
bwise121  Offline
Member
Joined: Sep 2003
Posts: 114
Sacramento, CA USA
Say you have a 14 gauge wire that has been greatly overloaded to the point that it melts the copper conductor.
What is happening at the atomic/electron level that causes this to happen. I'm trying to get a better picture of curent flow.

Thanks


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#130248 - 02/27/06 08:24 PM Re: Under the hood of melting wires  
JoeTestingEngr  Offline
Member
Joined: Nov 2005
Posts: 785
Chicago, Il.
Maybe I'm over simplifying things but I view it as two different issues:
1.) Resistive heating of the conductor.
2.) The temperature at which elements change to their molten or gaseous states.

You can melt a fuse element or vaporize it depending on fault currents and I'm sure we've all seen both types.
Joe


[This message has been edited by JoeTestingEngr (edited 02-27-2006).]


#130249 - 02/27/06 08:56 PM Re: Under the hood of melting wires  
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
nowhere usa
We could think about it like this:

One amp of current flow is equal to 6,280,000,000,000,000,000 electrons moving per second.

So if we say that 30amps of current flowing at a continous rate will melt a 14 ga wire, then 188,400,000,000,000,000,000 electrons moving per second would be our answer.

Make sense?


Dnk...


#130250 - 02/28/06 11:33 PM Re: Under the hood of melting wires  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
Mr. Wise, the simplistic answer is that the heat is caused by physical friction.


Larry Fine
Fine Electric Co.
fineelectricco.com

#130251 - 03/01/06 01:31 AM Re: Under the hood of melting wires  
Dave T  Offline
Member
Joined: Jan 2005
Posts: 155
Waukesha, WI, USA
My thinks that with all of those electrons trying to squeeze through that tiny wire the electrons just plain explode outward like a balloon when they can't make it to the other end of the wire. Or, using that water theory, when you try to put too much water pressure on a hose that can't handle ot the hose explodes.
To heck with that friction and heating theory.
Now back to my martini.


#130252 - 03/01/06 08:15 AM Re: Under the hood of melting wires  
WFO  Offline
Member
Joined: Sep 2005
Posts: 202
Cat Spring, TX
At one time I was confused by the fact that temperature increased resistance, since in almost all chemical applications where molecules bond, heat is considered a catalyst.

Then someone explained that it was merely a matter of the atoms getting farther and farther apart from expansion as they heated, thus making the "gap" the electron was required to jump larger and, therefore, increased the resistance.

I guess this could be taken one step further to the point that the atomic structure expands to the point the molecules no longer bond adequately, and go from a rigid state to a molten one.

....or maybe not [Linked Image]



[This message has been edited by WFO (edited 03-01-2006).]


#130253 - 03/01/06 05:41 PM Re: Under the hood of melting wires  
Alan Belson  Offline
Member
Joined: Mar 2005
Posts: 1,803
Mayenne N. France
Correct. Van der Waals
and London forces are weak molecular bonds tending to hold substances together as solids or liquids. Increasing motion of molecules due to raised temperature strains against these forces. Total breaking of the forces causes the substance to melt or boil at a specific temperature and pressure. The increase in temperature in a conductor carrying current comes from friction of the electrons passing. Electrons are not electricity, any more than water is pounds per square inch. You cannot bottle a kick up the ass; it's a force not a substance.
Not quite sure why electrical resistance increases with temperature in metals, because it decreases with temperature in carbon.

Alan


Wood work but can't!


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