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The input voltage is 220v in single phase.
How many watt consumed for Kanthal A1 (heat wire) AWG18 for 30m at 1400 degree Celcius ?
How many If I use NiCr 60 or 80 with AWG18 ?

Does anybody know the formula ? Does your formula apply for NiChrome wire ?

I read the following below and confused :
Formula between wire size and current
1000 watts, 220 volt, 52" length, Coiled Nichrome wire

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AWG 18 has a nominal diameter of 1.016mm, and a cross section of 0.8107mm^2. The resistivity of Kanthal A1 is 1,45Ω-mm^2/m at 20 celcius. So the total resistance of 30m will be 53.65Ω at 20 degr.

The temperature factor of resistivity Ct at 1,400 degr. is given by the manufactures as 1.05 so the resistance at this temeprature will be 56.34Ω. So the consumed power will be P=220^2/56.34 or about 860W.

1400 degrees is the maximum contius temperature that you can use A1. As for V80 this temperature is the melting point, so you can not use for the specific application. You can check now by yourself the use of Nichr 60 alloy.

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    \$\begingroup\$ @ Sidhi Ciang R=ρxL/A. ρ is the resistivity of the alloy in Ω-mm^2/m and it is given by the manufcturer under physical properties usually at 20 degr. Celc. \$\endgroup\$ – GR Tech Jan 3 '15 at 3:29
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    \$\begingroup\$ Correct....You didn't miss asomething. Here it is 5:30 in the morning and I miss to dring coffee....I will edit. Thanks \$\endgroup\$ – GR Tech Jan 3 '15 at 3:31
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    \$\begingroup\$ Formula for area from diameter is?? \$\endgroup\$ – Spehro Pefhany Jan 3 '15 at 3:37
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    \$\begingroup\$ @ Spehro Pefhany ..the usual one πxr^2....after the coffe!! \$\endgroup\$ – GR Tech Jan 3 '15 at 3:44
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    \$\begingroup\$ Diameter of AWG 18 is 1.016mm so r=0.508mm. Cross section area is 0.8107mm^2. Correct? 1,45x30/0,8107=53,65. Correct? \$\endgroup\$ – GR Tech Jan 3 '15 at 3:53
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Easy to work this out from first principles.

The formula for power is \$P = \frac{ V^2}{R} \$ where V is the RMS voltage.

The formula for resistance is \$ R = \frac{\rho L}{A} \$

So, simply find the resistivity of Kanthal A-1 at 1400'C, the diameter of AWG 18 wire (1.024mm) will give you the cross-sectional area and work out the watts, using your given RMS voltage and wire length. Pay attention to the units.

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