The strength of the magenetic field caused by current is a function of current and rate of change of current, not the material. Carbon is used in automobile ignition circuits for other reasons than prevention of noise (which is caused by the 'static' caused by the sparks at the plugs not by the magnetic field in the ignition wires. The magnetic field in wires of the ignition system is very low because the current is very low, although the voltages are very high. Magnetism caused by current is not lower in Carbon conductors for the same current.
Respectfully, Bob P.
