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David Lee
Guest
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 Posted:
Fri Dec 09, 2005 1:35 am Post subject:
Re: Seek resistance table for main flex |
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Dave Platt...
| Quote: | Run 20 amps through a heavy-duty extension cord, lose a few volts due to
IR
drop, and you can end up with quite a few tens of watts of heat to be
lost. Under prolonged load this might, perhaps, be enough to affect
the integrity of the cord's insulation somewhat, or even cause a
thermal burn.
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Somewhat more than somewhat! 13A through a typical coiled extension cable
(in a plastic drum) is enough to melt the drum and insulation - I've seen it
happen! My present 9m 13A extension cable is rated 13A fully unwound but
only 8A wound.
Excess extension cable should be neatly but loosely coiled to prevent a trip
hazard whilst maintaining adaquate cooling.
David
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Dave Platt
Guest
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| Posted:
Fri Dec 09, 2005 1:35 am Post subject:
Re: Seek resistance table for main flex |
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In article <972695BCD95A517E53A@66.250.146.159>,
JS <j_simmonmds@nomailthankyou.com> wrote:
| Quote: | Hmmm. Yes. :-)
I was hoping to use a compass deflection as a way of telling how much
heat/power was being lost in neatly wrapped coiled of mains flex.
Surely there is a loss of something due to the neatness - or perhaps
not?
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Lower probability of managing to "accidentally" trip an unwanted
in-law over the mounds of loose cable lying around on the floor? Some
would call that a significant loss :-)
Semi-seriously, though - I believe that the actual power loss in the
wire, and thus the total amount of heat generated, is as close to
identical in the two cases as makes no difference.
The reason for not coiling up high-amperage mains cable is probably
one of heat dissipation, rather than heat generation. If the cable is
lying out in a straight line, or just piled up loosely, it can shed
the waste heat effectively via radiation, conduction to the ground,
and convection into the air. If you coil it up on a spindle of some
sort, the heat generated in the inner turns of the coil will have no
easy means of escape... it can only get out via conduction through the
outer turns of the coil, which are rubber- or plastic-insulated and
thus have a high thermal resistance.
Run 20 amps through a heavy-duty extension cord, lose a few volts due to IR
drop, and you can end up with quite a few tens of watts of heat to be
lost. Under prolonged load this might, perhaps, be enough to affect
the integrity of the cord's insulation somewhat, or even cause a
thermal burn.
--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads! |
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Ian Stirling
Guest
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| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Seek resistance table for main flex |
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In sci.engr.lighting Franc Zabkar <fzabkar@iinternode.on.net> wrote:
| Quote: | On Thu, 08 Dec 2005 02:22:25 GMT, JS <j_simmonmds@nomailthankyou.com
put finger to keyboard and composed:
On Wed 07 Dec 2005 18:24:48, Victor Roberts
xxx@lighting-research.com> wrote:
But you must never use the cable whilst tightly coiled up
(unless you have deliberately overspecified its capacity). A
coiled cable has a much higher AC impedance due to induction and
can overheat alarmingly.
snip
I have often wondered about how much of an effect my very neat
coils of mains flexes for my PC was having! And I really do seem
to have a lot of devices which plug into the mains.
What about the magentic or ERF effects of a tightly coiled main
flex? Say, 12 neat-ish turns with a diameter of 5 or 6 inches
.... How much of a nuisance might such a thing be to electronic
equipment like my PC?
The magnetic field produced by any number of turns of mains flex is
zero. Think about it.
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For differential mode current only.
For common mode signals, like RFI on all three wires, probably not.
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Ian Stirling
Guest
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| Posted:
Sun Dec 11, 2005 4:18 pm Post subject:
Re: Seek resistance table for main flex |
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In sci.engr.lighting JS <j_simmonmds@nomailthankyou.com> wrote:
| Quote: | Table 4H3B gives the volt drop of the cable in mV/A/m. You
should allow for a maximum of 2% drop in voltage at the far end
of your flex.
I'm not sure *why* you would want to know the resistance per se,
but you can work out the resistance from these figures.
Hi Rumble
I was hoping to measure the resistence across the live/neutral pins
of the mains plug and then deduct the resistence of the main lead
(which is approx 10m of 1.0 mm^2).
From the result I was looking to know what the cold bulb resistence
is and from that infer the wattage.
The idea is to save opening up the housing and taking the bulb out to
measure the resistence.
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Unfortunatrely, the cold resistnace of a bulb has very little to do
with its hot resistance.
Design differences may even mean one with lower wattage has a lower
cold resistance.
Does your multimeter happen to have an AC current measurement? |
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