Hi,
No, not from motor. This ring was in the motor starter box. The motor is 25
feet away. This ring took the circuit to a breaker in the motor starter box.
The screw holding the ring was very tight. The back side of the ring looks
fine. The discoloring of the crimped barrel suggests the heat was generated
where the wire entered the barrel.
I can see shiny faces on the ring where the screw must have compressed the
ring to the terminal block.
Neither the ring or barrel was cracked. Before I opened the barrel I could
bend the wire and nothing in the barrel moved, the barrel crimp was quite
tight.
I will remove some insulation and see if there is a wire breaks, good idea.
The only vibration would be a small amount when the breaker open and closes.
The box was mounted on to plywood and that was on a cinder block wall.
Thanks,
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Upton, Shawn
Sent: Wednesday, March 31, 2010 4:23 PM
To: [log in to unmask]
Subject: Re: [TN] Failed Ring Terminal
Heat conducted up the ring terminal from the motor? What did the
backside of the ring look like--did it make good contact, or was it
lousy, causing higher current draw, which then over-heated the wire? I
wonder how far down the wire that corriosion goes--I wonder if the wire
resistance is high, causing the wire itself to be the heat source.
Lastly, is that ring terminal cracked? It looks like it is almost
broken in half. I also don't see a log of markings from the screw when
you removed it--I'd expect fresh marks, scratches, from the bolt as it
was removed. Might it be flex induced, cracking the ring, but also
creating a broken wire a few inches away from the ring terminal?
Shawn Upton, KB1CKT
Test Engineer
Allegro MicroSystems, Inc
[log in to unmask]
603.626.2429/fax: 603.641.5336
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, March 31, 2010 3:55 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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