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| On 9 Jun 2005 08:57:18 GMT, phil-news-nospam@ipal.net wrote:
quote:
>On Thu, 09 Jun 2005 00:49:32 GMT Bob <licku45@yqahoo.com> wrote:
>
>| Another suggestion to add.
>| Utility brouwn outs. They are becoming more and more common,
>| especially on hot days. Low voltage causes the motors to pull more
>| current, tripping the breaker. Once a breaker has tripped, it takes
>| less to make it trip the next time, and less the next time etc. etc. I
>| had to replace my breaker last year, it just wouldn't hold in when the
>| AC started.
>
>Thermal element degradation?
Probably. I like to think of it as "thermal memory". Most thermal
elements in breakers are bi-metal strips. As current flows, the strip
heats up and because one side expands faster than the other, it bends
and hits a spring loaded trip bar that activates the breaker
mechanism. Do that several times, and it no longer comes all the way
back to the original position, meaning it takes less time to trip
again.
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