Good post Marsh.
A good electrical engineer or electronics engineer use's a device
that is proven to protect the system he has designed.
Tom - W4BQF
At Sunday 03:17 PM 6/18/2006, you wrote:
>I'm reluctant to jump into the fray, but I guess I just cannot resist....
>
>I cannot think of an overcurrent protective device I've run across in the
>past 35 years working for a manufacturer of electrical controls and power
>distribution equipment that was not an inverse time curve
>device. In other words,
>the higher the overcurrent, the faster the device opens. Typically,
>fuses are
>quicker than circuit breakers because of the reasons Art mentions, no moving
>mechanical parts. Of course there are plenty of exceptions, such as
>time delay
>fuses and very fast-acting specialty circuit breakers.
>
>However, I do not understand where Art comes up with fuses being required for
>large industrial motor circuits. I can show him lots of large, up to 400HP
>on 480V 3-phase, motor applications where a circuit breaker, or more likely a
>magnetic trip only circuit breaker, feeds a motor starter that controls the
>motor. Sometimes both a circuit breaker and fuses are used in series. An
>example is adjustable frequency drive applications, where it is not
>uncommon to have
>fast-acting fuses on the input side of the drive even when the drive has an
>input circuit breaker. The fuses are there because they can clear a
>fault very
>quickly.
>
>One thing is for sure. Somewhere there is a time current curve for the fuse
>or circuit breaker you are considering for your application that
>tells you how
>fast the device will open based on the percentage of overload.
>
>The fuse versus circuit breaker debate has been going on for a long, long
>time, and nothing I'm going to write here is going to bring it to an end.
>
>73,
>Marsh, KA5M
>
>
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Tom
"I couldn't repair your brakes, so I made your horn louder."
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