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tomtruty
02-23-2009, 04:29 PM
I'm trying to understand the theory behind resistive ignition wires. According to Ohm's law a resistor limits current in a given system. Is that why radio noise is reduced when using resistance wires in place of simple copper wires? I'm assuming that limiting the current reduces RF emissions to an acceptable level?

Schurkey
01-13-2012, 09:48 AM
Yup. Voltage ionizes the gap at the plug and between rotor and cap., but without current flow, a resistor doesn't affect voltage. Once the gaps are ionized and conductive, current flows through a conductor which produces a magnetic field; reducing the amperage with a resistor weakens the magnetic field. Therefore less RFI emitted.

Another way to reduce the RFI is to build the conductor to form an electrical "choke"; and that's the theory behind helically-wound plug wires.

The third way is to allow the wires to produce RFI, but then use a metal shield to prevent the RFI from transmitting beyond the shield (Older Corvettes had the steel "box" around the distributor and plug wires; some plug wires have a steel braid as a shield that is then grounded to the engine.