Volt Wire Feed
 Working Union Carbide VI-252C Wire Feed Welder, 3 Phase, 250 Amp, 230/460 Volt US $400.00 
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How do I build a low-amperage circuit for standard 15-amp 120VAC electricity?
I want to plug into a standard household outlet and just take a fraction of an amp for a heater element (just a strip of NiCr wire). I don't understand how I can build a circuit to do that: A standard outlet feeds 120 volts at 15 amps into the circuit. To limit the amperage I would need a resistor that can dissipate almost (120V)^2/15A?! What am I missing?
The outlet provides 120 Volts of AC. That is equivalent to a kind of electrical pressure. The outlet is CAPABLE of providing 15 amps of current. How many amps actually flow depends on the characteristics of the appliance. In the simplest case, resistance (measured in Ohms) is the characteristic that determines the amount of current ( Amps ) that will flow.
OHMS LAW:
The current that will flow is equal to the voltage divided by the resistance. Amps = Volts / Ohms
Say you want the NiCr wire to just take a tenth of an amp from the outlet;
0.1 amps = 120 V / Unknown Ohms
Rearranging: Unknown Ohms = 120V / 0.1 A
Unknown ohms = 1200 ohms
That's the total ohms. If your heater wire is only say 100 ohms, you will need to add 1100 ohms in series. The power dissipated in the resistor will be 0.1 squared times 1200 = 11 watts.
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