Yikes! What did I start? I seem to have an affinity for this - my recent
for sale post touched off a smoking shack debate.
Nonetheless, thank you again to all who responded. I am going to go ahead
and mount it in a box and attach with spade connectors.
Kirk
AI4PZ
On 6/18/06, Rideout Family <wa6ipd@dslextreme.com> wrote:
>
> Marsh, the reason fuses are required with motors is the short circuit
> current or AIC (ampere interrupting capacity). It would not be unusual
> for a three phase 40hp motor to fail and have a short circuit of 100,000
> amperes. The maximum rating of circuit breakers is 50,000 AIC so the
> breaker will explode. Fuses for 40hp motors would be required to have
> ratings of 250,000 AIC. Next time you visit Home Depot check their
> fuses you will find several price ranges which are related to the AIC.
> As for 400hp motors they sometimes use what looks like a circuit breaker
> but is only a disconnect and an integral part of the unit is a fuse.
> All large motors are protected by fuses.
>
> Best
>
> Art
>
>
> KA5M@aol.com 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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> >
> >
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