Today's Message Index:
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1. 10:46 AM - Re: Warm Extension Cord (Robert L. Nuckolls, III)
2. 04:25 PM - Re: Warm Extension Cord (user9253)
Message 1
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| Subject: | Re: Warm Extension Cord |
At 10:50 PM 5/13/2016, you wrote:
>Yeah, short, incomplete response. I know better. Mea Culpa. (did I
>say that correctly?)
>
>I assumed the resistive thermal rise and lack of cooling from a pile
>of cable were a given.
>
>I have foggy memories of stories from an ancient electrical
>instructor, possibly unfounded, of inexperienced electricians
>separating A/C phases in conduit resulting in catastrophic thermal failure...
Interesting . . . I'll have to ponder that a bit.
I too have an anecdotal recollection of noises
emanating from overhead conduits when some high-
inrush machine was turned on back in Electro-Mech's
shops.
After mentioning it to one of the grey-beard
electricians who came out to add some outlets,
he explained that when the installer pulls three
separate conductors into a conduit, the electromagnetic
repulsion between adjacent conductors is free to
initiate some degree of 'thrashing about' within
the conduit.
He allowed as how it didn't make much difference
in a factory environment . . . but when his
company ran heavy duty wiring over, say, the
suspended ceilings of an office, their practice
was to pull in twisted trios so that the
conductors were not so free to move away
from each other.
Years ago I had a video taken of a large
loop of wire laying on a floor that was suddenly
energized with a very high current. The
loop of wire writhed on the floor like
a giant snake.
There's a youtube video that demonstrates
the potential for attraction/repulsion
forces between two conductors.
https://youtu.be/GW7PvSR9VUo
Of course, this is a purely mechanical
consequence of magnetic forces. The heating effect
you cited is another matter. The only thing I
can think of right now is that large AC
currents not flowing in equal-opposite,
close-proximity would induce eddy-currents
in the surrounding conduit which can only raise
the temperature of the conduit.
That would be an interesting physics lab
experiment. Thanks for posing the hypothesis!
Bob . . .
Message 2
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| Subject: | Re: Warm Extension Cord |
Years ago I took a college course on the National Electrical Code. The instructor
was an electrical inspector. He told about inspecting the electrical installation
in a commercial building. The installer had done a very neat job with
all of the white neutral wires in one conduit and all of the hot wires in another
conduit coming from the electrical service panel. After the building was
occupied, the tenant called the inspector complaining about hot conduits.
The installer had to come back and rewire the panel with the hot and neutral wires
from each circuit sharing the same conduit.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=456268#456268
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