Actually YOU were, when you asked me how much electricity "that mess actually
used".
That mess was the end of that 40 ft run of conduit. Whatever, I can do
calculations
on most anything.

>The discussion was about what happens with a single

>connection inside that junciton box. If it is a high

>resistance sufficient to cause even a slight reduction

>in the power available to other loads on the circuit, it

>is going to get hot and either burn through and become

>an open, or start a fire.

Sorry, Pop, you lose again. Actually the thread started out about a hot conduit
and
morphed into your "hot contact flambe'" theory. Whatever, let's do a contact.

How 'bout this one?

http://www.neon-john.com/images/Burned_contact.jpg

That contact is about 1.5" tall average, and about an inch wide. The surface
area of
one side is therefore 1.5 sq inches. For both sides, 3 sq inches. Let's add
another
square inch to account for the mating blade that isn't visible in the photo, for
a
total of 4 sq inches or 0.333 sq ft.

I've measured that blade tip at over 600 deg with a infrared pyrometer. Since
the
heating is uneven, especially along the blade, let's use 450 deg as an average
temperature. And since the box gets hot, let's use 30 deg as the ambient. This
is
conservative since when I made the measurements I had to have the door open and
that
exposed most of the contact to 20 deg ambient. We'll stay conservative. The
emissivity of oxidized copper is 0.98 according to my table. We now have enough
to
compute the radiated energy.

Remember this page?

http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/stefan.html#c3

Plugging all that in, the result is 96.5 watts. Again assuming twice the
convective
losses or 193 watts, the total comes out to 289 watts.

That seems reasonable, as in the heat of summer I've had to open the box and
place a
fan on it to keep conducted heat from blowing the fuse. It also seems
reasonable for
how hot a metal box that size would get with a 300 watt heater inside.

Cost

Let's use the same assumptions from my last post. 80 hours a week, 4 weeks in
the
month or 320 hours in the month. 0.289kW * 320 hours is 93kWh. At 9 cents a
kWh,
that's $8.34 for the month. Which is, last time I looked, > 20 cents a month.

So. Again, feel free to plug in any numbers that you like; I've held your hand
and
led you through the methodology. While you're cogitating, keep in mind that I
took
no credit for losses through the bulk of the blade, the hinge or the fuse and
holder.
Since enough heat conducts down the blade to contribute to the fuse's melting
below
its amp rating, that amount of heat is non-trivial.

Regardless of any assumptions you might choose, this one hot connection certainly
used more than your "20 cents a month" claim. Strike 2.

Nor does your claim withstand scrutiny that a hot connection that is dissipating
significant power will burn up. Strike 3. You're outta here.

Such a hot joint IS a risk but not of fire at this power level. The only real
risk
is of an outage if the thing finally oxidizes sufficiently that it doesn't make
contact anymore or that it arcs and melts. No fire possible inside that metal
switchgear.

The risk of outage and in larger gear, fire or explosion AND the operating cost
of
the joint is why companies hire people like me to do energy audits and thermal
scans.
The main driving force with every client I've ever had was cost - cost of an
outage
and cost of operating that hot joint.

>You've compared grapefruit and oranges, but we were

>talking about apples.

So now we talk about apples, only for you to demonstrate that you don't know them
either. Every time you open your yap you dig your ignorance hole a bit deeper.
Why
don't you give it a rest before you bury yourself (deeper) in stupidity.

John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Okay, okay, I'll take it back ... UNfuck you!

Posted by Mike on January 27, 2008, 5:47 pm

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> let's go back to that Stefan-Boltzmann calculator and do a little

>math.

Forget Stefan-Boltzmann and look at the volts, amps and ohms *that* is
what matters.

--

Posted by on January 27, 2008, 7:59 pm

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>> let's go back to that Stefan-Boltzmann calculator and do a little

>>math.

>Forget Stefan-Boltzmann and look at the volts, amps and ohms *that* is

>what matters.

Actually, it is a good fire, a cold one, and a suitable wench that
matters.

Posted by Stormin Mormon on January 25, 2008, 9:31 am

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Thank you for a (second) real life proof.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
.

Really? Then according to your expert theory, my restaurant ought to have
burned
down long ago.

http://www.neon-john.com/images/Wiring_overload.jpg

That photo is of what is left of the original 40s vintage 3 phase indoor
meter box.
Long since bypassed as a meter base, it still passed up to 300 amps at
times. That's
either #4 or #2 cloth covered, rubber insulated wire in the service
entrance. #4, I
think. It's obviously been hot enough to slag the rubber insulation but
somehow it
just keeps on truckin'. Of course, the wire is in rigid conduit and despite
your
declaration to the contrary, steel still doesn't burn very well.

That conduit has been too hot to touch on occasion. I monitored it closely
in the
summer time. I'd have loved to have replaced it but the city says that I
can't do my
own electrical work and I'm not about to pay someone else to do it so...
It's been
there since the 40s and it'll probably be there until the building is torn
down.

Perhaps you ought to look at the other post I made in this thread about how
to
compute irradiative losses from a hot object. The concept is simple enough
for
someone even of your caliber to understand.

Maybe you ought to get your code book out too. At various places it
discusses the
losses involved in various wire and cable temperature rises.

John

--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Nothing in life is to be feared. It is only to be understood. -Marie Curie

Posted by Floyd L. Davidson on January 25, 2008, 1:37 pm

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>Thank you for a (second) real life proof.

So where is the connection that got hot in his example????

>--

>Christopher A. Young

>Learn more about Jesus

> www.lds.org

>Really? Then according to your expert theory, my restaurant ought to have

>burned

>down long ago.

>http://www.neon-john.com/images/Wiring_overload.jpg

>That photo is of what is left of the original 40s vintage 3 phase indoor

>meter box.

>Long since bypassed as a meter base, it still passed up to 300 amps at

>times. That's

>either #4 or #2 cloth covered, rubber insulated wire in the service

>entrance. #4, I

>think. It's obviously been hot enough to slag the rubber insulation but

>somehow it

>just keeps on truckin'. Of course, the wire is in rigid conduit and despite

>your

>declaration to the contrary, steel still doesn't burn very well.

>That conduit has been too hot to touch on occasion. I monitored it closely

>in the

>summer time. I'd have loved to have replaced it but the city says that I

>can't do my

>own electrical work and I'm not about to pay someone else to do it so...

>It's been

>there since the 40s and it'll probably be there until the building is torn

>down.

>Perhaps you ought to look at the other post I made in this thread about how

>to

>compute irradiative losses from a hot object. The concept is simple enough

>for

>someone even of your caliber to understand.

>Maybe you ought to get your code book out too. At various places it

>discusses the

>losses involved in various wire and cable temperature rises.

>John

>--

>John De Armond

>See my website for my current email address

>http://www.neon-john.comhttp://www.johndearmond.com <-- best little blog on the

net!

>Tellico Plains, Occupied TN

>Nothing in life is to be feared. It is only to be understood. -Marie Curie

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

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