On Fri, 25 Jan 2008 09:35:40 -0900,
(Floyd L. Davidson) wrote:
Neon John wrote:
The conduit between the meter base and that box is about 40 ft of 2" rigid conduit.
Learn to read and respond to the topic of discussion.
You are talking about a 40 foot run of cable. Nobody
else is.
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...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 ... UN**** you!