Paul,
I agree. Soldering takes SO much longer and it can make a mess of the
insulation, looks bad. But, if this terminal had been soldered it would
still be working.
Though, 40 Years in my Dad's barn is more than I would asks of ANYTHING!
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Edwards
Sent: Wednesday, March 31, 2010 5:24 PM
To: [log in to unmask]
Subject: Re: [TN] Failed Ring Terminal
Bob,
A soldered crimp terminal is best for high reliability joints...
The surface of the individual strands of wire that makeup the conductor
oxidize (and/or corrode) because they are exposed to the environment and
increase the strand to strand resistance... As the current travels from the
conductor core to the contact surface area of the crimp connector it
differentially heats the strands in the conductor until you preferred
current paths... The Cu then starts to thermal cycle under load and causes
crystallization and failure of the Cu...
A solid solder joint eliminated this problem because of the soldered Cu
interfaces are complete involved in the solder joint.
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, March 31, 2010 12:55 PM
To: [log in to unmask]
Subject: [TN] Failed Ring Terminal
Hi,
Why would a crimped ring terminal fail and over heat? Can anyone suggest
failure modes as to why the resistance would increase?
I would guess a soldered connection would be better?
See www.kondner.com/files/failedringterm.jpg
That insulator was yellow at one time it is now brown and the insulation at
that end of the wire is very brittle. The wire size is #10.
This ring terminal came from a Furnas Electric motor starter for a 5hp 240V
AC motor that draws about 28 amps. It was installed back in 1968. It was
installed in a dingy barn in a silo pit where most of the steel enclosures
are covered with rust. All kinds of nasty odors as there are plenty of cows
in the area. It is quite amazing that it went this long, but I wonder why it
failed.
The crimp seemed tight but it had obviously over heated. Other such ring
terminal on the same circuit are fine. The crimps were made in the factory
and not by some guy with a simple hand tool.
I ground off the edges which allowed me to open the crimp with minimal wire
damage. I was surprised that much of the wire looked quite clean.
I am just curious what folks would suggest.
Thanks,
Bob Kondner
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