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If I have a copper wire and a nichrome wire of the same gauge (e.g. 30 awg) with the same current passing through them. why does the nichrome heat up significantly.

Also, the length of the wires are the same (e.g. 1 foot), the voltage is the same (e.g. 12 volts). The current is being varied by PWM.

Question: What is it about nichrome that causes it to heat up so much?

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Nichrome wire has far, far higher resistance per unit length at a given cross section. It's an alloy chosen for that property.

The power dissipated in a resistor is the product of the resistance and current, so a larger resistance at the same current means more power dissipated as heat.

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  • \$\begingroup\$ So it's about the metals resistance, not the current. So if I passed 500V through a 1K resistor it should catch fire? \$\endgroup\$ – user3045 Apr 28 '13 at 15:50
  • \$\begingroup\$ So if I pass 1.5 Amps into 1 inch of nichrome it will reach 300 Degrees same as if I passed 1.5 Amps into 1 foot. \$\endgroup\$ – user3045 Apr 28 '13 at 15:56
  • \$\begingroup\$ To a first order, the amount of heat which something like an (uncoiled) wire can shed to its environment is proportional to its length, and so is its overall resistance. So the temperature reached would depend on the current, but not on the length. However, the total resistance, total power, and voltage to achieve that current would increase with the length. In short lengths though, heat loss through the electrical connectors would be a factor. \$\endgroup\$ – Chris Stratton Apr 28 '13 at 16:01
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Nicrome wire has a high resistance, it has a high melting point and it can remain red hot for a long time without getting oxidized or 'burning out'

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  • \$\begingroup\$ Yeah, the important attributes of Nichrome are three: High resistance, high melting point, and chemical inertness. \$\endgroup\$ – Hot Licks Jan 16 '15 at 13:12
  • \$\begingroup\$ @HotLicks I think there are 2 more good properties in nichrome - non-magnetic and mechanical properies. I didn't mentioned chemical properties in my answer, I added it now, thanks for pointing that. \$\endgroup\$ – Kamil Jan 16 '15 at 13:20
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Nichrome is an resistive alloy. It has very useful properties as heating wire:

  • high melting point
  • high resistance
  • chemical inertness
  • non-magnetic
  • good mechanical properties

The reason why it heats up more is high resistance. In comparison to good conductors like copper - it is possible to transform more electrical energy into heat by using wire with same gauge and length at same current or voltage.

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