Fw: (ET) fuses and breakers

["Randy Kanary" <rj kanarysweb com>]

RJ Kanary@ Bandi Bros. Inc. ATRA ® Member Shop
Member TRNi 1&2 Since 1998
ASE® Certified Master Auto Technician Since 1992
Member Tech Line Associates Since 1987
rj kanarysweb com




----- Original Message -----
From: Randy Kanary <rj kanarysweb com>
To: Larry Elie <lelie ford com>
Sent: Monday, November 01, 1999 1:15 PM
Subject: Re: (ET) fuses and breakers


Larry, the 40 or 50A circuit breaker "under the hood" is the one that
protects the charger wiring in the event of a rectifier short. [C.B.2]
.C.B.1, the 100A Klixon®, primarily provides .armature overcurrent
protection, but when it opens it kills just about everything. The only 
major
load it does not protect directly is PTO. Hope this helps!

RJ Kanary@ Bandi Bros. Inc. ATRA ® Member Shop
Member TRNi 1&2 Since 1998
ASE® Certified Master Auto Technician Since 1992
Member Tech Line Associates Since 1987
rj kanarysweb com




----- Original Message -----
From: Larry Elie <lelie ford com>
To: <elec-trak cosmos5 phy tufts edu>; 'David Howard' <howie sssnet com>
Sent: Monday, November 01, 1999 9:57 AM
Subject: RE: (ET) fuses and breakers


Thanks for setting us straight Dave.  I was the confused individual who
proceeded
to spawn confusion.  I have done fuse testing (20+ years ago) but never 
done
a
breaker test in my life.  I should have guessed an I square R for the power
in the
'passive' device.  Duh.

Now the problem.  Even today, someone posted shunt values for the meter of
an
E-20.  Note the E-20 has a 50 Amp breaker on the armature.  The values for
the
green range extended to 75 Amps.  This compares rather well to the values I
saw with a Hall-Effect Clip-on (to my Fluke digital) on my E12.  The yellow
range
extended to 121 Amps, and the red ended at 156 amps.  I was able (by 
pushing
on a dirt pile with the blade to nearly pin the meter (~200 Amps at Hall)
for tens of seconds.
I have pushed gravel for over an hour between the upper green and yellow.
These are
on the order of 100 Amps, or more than twice the value of the 40 Amp 
breaker
in my
E12.  I have never tripped it.  Someone else posted a clip-on value of 600
Amps, which
I think should take out the fusible link, but it didn't.  Even for a
'slow-blow' breaker, I have
a hard time understanding how this could work.  Secondly, even at 100 Amps,
we
are only talking about something like 5 HP; and GE's 'rating' would be as
bad as
the Sears ratings on their saws.  At 40 amps, my GE would be about 2 HP,
making
Sears look honest.  Sure, part of the 'rating' might include the deck
motors, but they
are only about 1 HP (by my calculations... now suspect) each.  I do design
of high-field
devices (clutches) for part of my job, and I am having some real problems
here.

The bottom line is how can an E-20 win in a tractor pull?  And how does a 
40
Amp breaker
handle 100 Amps for over an hour?

Larry Elie


----------
From: David Howard[SMTP:howie sssnet com]
Sent: Sunday, October 31, 1999 7:39 AM
To: elec-trak cosmos5 phy tufts edu
Subject: (ET) fuses and breakers

    There has been alot of confusion and misinformation on the fuses and
breakers.  The equation stated before for heating in an electrical circuit
is not right.  The temperature in a circuit is related to the current (I)
squared times the resistance of the circuit or device in the circuit or I^2
* R. Someone wrote about the different fuse voltage ratings and thinking
that the higher voltage rating ment that you had to have that voltage and
current to cause the fuse to blow.  Not true!!!  the voltage ratings show
what type of fuse is needed to ensure that when the fuse operates and  that
the circuit opens.  Whenever a fuse opens, an arc is created across the
opening element.  If the gap is not large enough then the circuit can
actually stay energized instead of opening.  This gap that is required is
determined by the system's voltage.  So whether you have a 30 amp 
automotive
fuse ( rated at 12 V ) or a household fuse at 30 amp ( rated at 120 or 220 
V
) they both blow at 30 amp.  It is just that the automotive fuse is smaller
than the household fuse because it only has to ensure an open circuit at 12
V instead of 120 V or 220 V.

    A fuse is a relatively  instantaneous device. Up to about 102 % of its
rating a fuse will work.  Above that, the element inside will rapidly melt
and separate, opening the circuit.

    A breaker, on the other hand does not instantly open when its rating is
exceeded.  The most common breaker that we see is the Bimetalic element.  
It
works by having two different metals that heat diffently.  As they heat 
they
move and cause the circuit to open circuit.  As the metals cool they move
back and the circuit can be made again.  When a breakers rating is 
exceeded,
the breakers opertate on what is known a an I^2 T curve.  That is current
vs. Time curve.  The higher the current the faster the breaker trips until
it is actully an instantaneous device also.

    The same thing applies the the breaker elements.  Because the 
temerature
of the element is I^2*R, it does not matter what the voltage rating of the
breaker. It will still go at the same current.

    There are different types of breakers and fuses.  Some are "quick blow"
and some are "slow blow".  depending on your application you might need to
experiment with differnt types to find on that provides for turning the
component on and still provide running protection.

    If you have any questions please respond.  I work in the electrical
testing and maintenance field and do this for a living.  We have a high
current machine that we use to test 480 V breakers.  This machine only puts
out .5 to 2.0 V while providing up to 50,000 amps. So we trip breakers 
every
day with low voltage but the proper amount of current.

Dave Howard
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