RE: poor power factor coils

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 07:25 AM 4/19/2004 -0600, you wrote:
>Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
> >WIth my microwave oven transformers, 2 of them almost shorted on
> >their outputs tends to cause my 35 amp breaker to blow. However it almost
> >never blows the 16 amp fuse.  WOuld this be because of the high peak
> >currents from a poor power factor?
>
>Sort of all of those things ;) Firstly, a fuse has a different response
>characteristic to a breaker. The reason being that the fuse has to heat up
>before it can melt, but the breaker is operated by magnetic forces that work
>instantly. A 16 amp fuse will stand 32A or more for a minute or so, whereas
>a 35A breaker usually pops at 35A no matter what. So you often see overloads
>popping a breaker before they blow a fuse.

The circuit breakers in your house have a time/overload characteristic much 
like a fuse.  A 200% overload will trip a lot faster than a 120% overload. 
They're also thermally actuated (bimetallic element and snap action switch).

In industrial applications, you'll see magnetically operated switches or, 
more commonly, combined magnetic and thermal switches.  They allow you to 
set the peak current separately from the average current (which is 
important when starting motors under load, where the starting current might 
be 3-4 times the running current)