Hard wire

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mickeyrench

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edison, n.j.
Is it normal for a wire in this case a #4 thhn cu to get a solid hard feeling to it where it doesn't feel like a stranded wire. This wire has been in service for 12 years on 3 phase 460 v vfd. I checked at 4 locations where it connects to the fuses and in and out of the vfd the first 10 inches or so the wire has a completly different feeling to it and I would like to know is this something to be concerned about?
 
Sounds to me like it has been the victim of a good deal of overheating through the years. The overheating has been at (or near) the points connection, so the wire in the middle has not seen the same damage. Loose connections can get you there, for one example.


Can you tell if the hard feel has to do more with the insulation becoming hard, then with something about the copper becoming hard?
 
Can't really tell if it is insulation or the wire itself. We were having a little problem with the vfd falling out while running and i was looking every where for the cause. Tech says its a board ,and we are still waiting for him to get one.
Thanks for the help.
 
Copper is heated to anneal it and make it softer, not harder. Although it requires over 1000 degrees F. Oxidation and vibration will make copper harder. I would say the heat hardened the insulation.
 
Some wire is shipped out as hard drawn copper sometimes. Especially when you re using the precut mc whips it creates havoc on ones fingers when terminating /Devicing we did a Mariot hotel where this was used and your hands are ground chuck by the end of the day eliminating some of the labor saved by using pre cut tails for a 400 room hotel.
 
quogueelectric said:
Some wire is shipped out as hard drawn copper sometimes. Especially when you re using the precut mc whips it creates havoc on ones fingers when terminating /Devicing we did a Mariot hotel where this was used and your hands are ground chuck by the end of the day eliminating some of the labor saved by using pre cut tails for a 400 room hotel.
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I remember years ago we had a lot of extra hard wire. I never decided if it was some cheap manufacturing process, or if it sat in a warehouse so long it oxidized. This is a big problem with soft copper tubing in coils. If they set a few years you will kink them trying to unroll it. In refrigeration we occasionally have to heat up some copper til it is dull red(1150 deg. F) and when it cools it is as soft as new copper. You have to run nitrogen through it to keep down the carbon soot, the same as if you were brazing it.
 
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ZZZ said:
Copper is heated to anneal it and make it softer, not harder. Although it requires over 1000 degrees F. Oxidation and vibration will make copper harder. I would say the heat hardened the insulation.
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If copper is brought up to a certain temperature, it can change the annealing of the copper and the result will be the copper gets harder.
This process may not be called annealing, but none the less, it still occurs.


I am not sure of the temperatures, but this I learned in one of my classes many years ago.
 
I've seen this happen where a bad connection in a wirenut overheats. A few inches of the copper wire becomes very hard from the heat. It's not the insulation hardening, because the insulation has melted off the wire.
 
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