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nuckolls.bob(at)aeroelect
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 Posted: Mon Aug 18, 2014 6:44 pm Post subject: Real life lessons in wire ratings . . . |
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Last weekend, Dr. Dee and I spent Friday/Saturday
supporting our son's shaved ice and cotton candy
business during "Old Settlers Days" in Mulvane, KS.
Temperature in upper 90s. Shaved ice trailer with
lights, rooftop a/c, freezer and shaved ice machine
running on ac mains through 100', 12AWG extension
cord not unlike that pictured below. Total current
draw on the order of 13 amps.
[img]cid:.0[/img]
Approximately 70' of cord was spooled out leaving about
30' still coiled on the reel. After 3 or 4 hours operation,
a vendor on the row behind us asked if that 'smoke and
bad smell' was something to be concerned about.
I swapped out the smoking cord for a spare.
I un-spooled the rest of the cord and discovered that
when not allowed the benefits of cooling air, the wrapped
up coils got pretty hot. The cord that was spooled out
was warmer than ambient but not markedly so. Voltage
at plug end under load was 124 volts . . . inside trailer
it was 117 volts for a round trip drop of about 7 volts.
Nonetheless, insulation on the poorly cooled wires
inside the yellow jacket fused together. In some places
the yellow jacket was breached and/or fused to adjacent
turns.
This cord reel is designed to encourage rolling out only
that cordage which is needed . . . but if you're going
to load it to near max ratings, then it's a good idea
to un-spool the entire length.
A profound demonstration of how temp rise on
a wire is exacerbated by constriction of free air cooling.
I cut off the damaged 30', installed a new plug and
left the full in-service length of cord laid out on
the ground for the rest of the event. Voltage drop
went down to just over 5 volts on the shortened cord.
Bob . . .
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raymondj(at)frontiernet.n
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| Posted: Tue Aug 19, 2014 11:59 am Post subject: Real life lessons in wire ratings . . . |
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Was the insulation on the individual conductors compromised? Was there
any indication that there was the threat of an actual short occurring or
was it just a matter of the outer jacket melting?
Who was the manufacturer and/or what brand name was the cord sold under?
Raymond Julian
Kettle River, MN
The things we admire in men, kindness and generosity, openness, honesty,
understanding and feeling are the concomitants of failure in our system.
And those traits we detest, sharpness, greed, acquisitiveness, meanness,
egotism and self-interest are the traits of success. And while men
admire the quality of the first they love the produce of the second.
-John Steinbeck, novelist, Nobel laureate (1902-1968)
On 08/18/2014 09:43 PM, Robert L. Nuckolls, III wrote:
| Quote: | Last weekend, Dr. Dee and I spent Friday/Saturday
supporting our son's shaved ice and cotton candy
business during "Old Settlers Days" in Mulvane, KS.
Temperature in upper 90s. Shaved ice trailer with
lights, rooftop a/c, freezer and shaved ice machine
running on ac mains through 100', 12AWG extension
cord not unlike that pictured below. Total current
draw on the order of 13 amps.
Emacs!
Approximately 70' of cord was spooled out leaving about
30' still coiled on the reel. After 3 or 4 hours operation,
a vendor on the row behind us asked if that 'smoke and
bad smell' was something to be concerned about.
I swapped out the smoking cord for a spare.
I un-spooled the rest of the cord and discovered that
when not allowed the benefits of cooling air, the wrapped
up coils got pretty hot. The cord that was spooled out
was warmer than ambient but not markedly so. Voltage
at plug end under load was 124 volts . . . inside trailer
it was 117 volts for a round trip drop of about 7 volts.
Nonetheless, insulation on the poorly cooled wires
inside the yellow jacket fused together. In some places
the yellow jacket was breached and/or fused to adjacent
turns.
This cord reel is designed to encourage rolling out only
that cordage which is needed . . . but if you're going
to load it to near max ratings, then it's a good idea
to un-spool the entire length.
A profound demonstration of how temp rise on
a wire is exacerbated by constriction of free air cooling.
I cut off the damaged 30', installed a new plug and
left the full in-service length of cord laid out on
the ground for the rest of the event. Voltage drop
went down to just over 5 volts on the shortened cord.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Tue Aug 19, 2014 4:22 pm Post subject: Real life lessons in wire ratings . . . |
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At 02:58 PM 8/19/2014, you wrote:
| Quote: | --> AeroElectric-List message posted by: rayj <raymondj(at)frontiernet.net>
Was the insulation on the individual conductors compromised? Was there any indication that there was the threat of an actual short occurring or was it just a matter of the outer jacket melting? |
No, all levels of insulation was being deformed.
Temperatures were high enough to cause visible
smoke. No short before it was unplugged.
| Quote: | | Who was the manufacturer and/or what brand name was the cord sold under? |
It's not a NEMA graded cordage but no reason to
believe it's not adequate to the ratings common to
the wire (12AWG). The portions that were laying
out on the ground were 'happy' . . . only those
turns deprived of opan-air cooling got into
trouble. Wire bundles in airplane will do the same
thing.
[img]cid:.0[/img]
Here's a piece of 22759, 10AWG in a bundle
'protected' by silicone impregnated fiberglas
transiting a hot environment. Got hot enough
for the Tefzel wrap to separate at edge bond.
Bob . . .
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