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I couldn't figure out the maximum amount of continuous current can a 4 meter 0.085 Ohm wire carry? Also, for 300 milliseconds can it handle 100Amps? Provided a powerful fan cooling it?

What about 100A continuous current with a cooling unit(industrial fans)?

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  • \$\begingroup\$ 300ms is duration, what is the duty cycle? How much voltage drop across the wire can you live with? \$\endgroup\$ Apr 20 '15 at 16:05
  • \$\begingroup\$ What size (diameter) is the wire? \$\endgroup\$ Apr 20 '15 at 16:06
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    \$\begingroup\$ Is that 0.085 measured resistance, or 0.085 ohms per foot, per inch, per mile, per kilometer, per square ironing board...? \$\endgroup\$
    – Majenko
    Apr 20 '15 at 16:12
  • \$\begingroup\$ Not sure how to calculate the duty cycle haven't worked out the data yet. The diameter of the wire is 1mm, 0.085 is calculated resistance in mm, used the formula R = pL/A converted everything to mm before that. \$\endgroup\$
    – Pupil
    Apr 20 '15 at 16:18
  • \$\begingroup\$ That's 0.085 ohms per mm? \$\endgroup\$
    – Majenko
    Apr 20 '15 at 17:26
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If copper wire, that's about an AWG 18 wire. 100A is above the fusing current of an AWG 18 copper wire, so without some kind of cooling the copper will actually melt with 100A continuous.

300ms (with sufficient time between pulses for the wire to cool) might be "okay" due to the heat capacity of the wire (you'd have calculate it out) but the wire will get very hot and probably smoke a bit, and perhaps could set things on fire. Any insulation other than something like a quartz tube might be degraded or destroyed, and the wire will tend to oxidize and droop under gravity.

If the wire is other than copper then then answers will be somewhat different, but the approach would be the same.

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  • \$\begingroup\$ Do you know of any conductor that has the potential to surpass copper by major folds? I know of graphene which I heard has the potential to carry 1000x of copper at a much lighter lighter weight. \$\endgroup\$
    – Pupil
    Apr 20 '15 at 16:10
  • \$\begingroup\$ @Key: use a superconductor, much lighter and much easier to handle and produce than graphene. \$\endgroup\$
    – PlasmaHH
    Apr 20 '15 at 16:17
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    \$\begingroup\$ @Key what are the actual requirements? Why not just use a fatter copper wire? \$\endgroup\$ Apr 20 '15 at 16:36
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    \$\begingroup\$ @SpehroPefhany, your wiki AWG link also lists fusing current for shorter times. 1 sec and 32 ms. As a "back of the envelope" calculation, I find 1 meter of AWG wire has a volume of ~0.79 cm^3, heat capacity of copper is about 3.5 J/(K*cm^3) so 2.75 J/K. and I get 100 A for 1 sec would raise the temp by less than 100 C .(assuming no math mistakes.) If I use the 1 sec. fusing current I get a temp rise of ~800 C. That seems reasonable. \$\endgroup\$ Apr 20 '15 at 17:40
  • \$\begingroup\$ @GeorgeHerold Seems reasonable to me, and fits with everyday experience in things like car jumper cables. \$\endgroup\$ Apr 20 '15 at 17:42

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