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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: What's wrong with the aluminum wiring? posted by GTF on July 8, 2006 at 20:32:52:
Aluminum hardens with time as it goes through a phase of recrystallization. It takes years and years at ambient temperature, but it does and it goes.
Then, it becomes much harder but brittler, and strained areas, like under a tight screw in any power interconnect, are prone to breaking or to flowing aside. Result, the links are no more tight.
As soon as local pressure becomes on the order of the atmospheric pressure, bare aluminum areas (where oxyde was once expelled off by strain when the screw was tightened ) oxidize.
Since aluminum oxyde is an excellent insulator, the link resistance increases (furthermore since many aluminum threads are broken). After years, you are at risk of a localized heating then fire.
That's why EU codes forbid aluminum wiring. I don't know for the US NEC.
Obviously, the former doesn't apply to large thick aluminum bus bars, never found in a residential flat or house anyway.
At a time, some manufacturers tried to mitigate the problem by alloying aluminum with meatls like nickel or cobalt which are known to "lock" the recrystallization process by increasing its activation energy, so it would take centuries instead of years. But it badly affects the ohmic resistivity, so...
That said, since copper prices are skyrocketting, I bet some chemists and metallurgist will create a new aluminum-based alloy. Not yet now to my knowledge.
BTW, airborne wiring uses only copper (sometimes silver plated), in spite of its weight. A plane does vibrate a lot...
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Follow Ups
- Nothings as thick bar bus; but a no-no as wire - Jacques 09:37:43 07/09/06 (8)
- The explanationsI read were slightly different - Soundmind 11:24:50 07/09/06 (7)
- No arcing until the final fire! - Jacques 12:27:09 07/09/06 (5)
- Re: No arcing until the final fire! - chris_w 02:38:45 07/16/06 (3)
- This is much closer to my experience, arcing can continue for a considerable time nt - Soundmind 18:05:45 07/18/06 (0)
- Yep - Ted Smith 10:03:16 07/16/06 (1)
- Re: Yep - Soundmind 18:22:51 07/18/06 (0)
- you will find a similar problem with underfloor "flatwire" in open landscape offices - Soundmind 13:57:25 07/09/06 (0)
- If their installed correctly there's no problem. - GTF 12:05:17 07/09/06 (0)
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