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High tension leads or high tension cables or spark plug wires or spark plug cables are the wires that connect a distributor, ignition coil, or magneto to each of the spark plugs in some types of internal combustion engine. "High tension lead" or "cable" is also used for any electrical cable carrying a high voltage in any context. ''Tension'' in this instance is a synonym for voltage. High tension leads, like many engine components, wear out over time. Each lead contains only one wire, as the current does not return through the same lead, but through the earthed/grounded engine which is connected to the opposite battery terminal (negative terminal on modern engines) high tension may also be referred to as HT. ==Description== Spark plug wires have an outer insulation several times thicker than the conductor, made of a very flexible and heat-resistant material such as silicone or EPDM rubber. The thick insulation prevents arcing from the cable to an earthed engine component. A rubber "boot" covers each terminal. Dielectric grease can be used to improve insulation; a small amount can be applied in the inside of the rubber boot at each end of each wire to help seal out moisture. Printing on spark plug wires may include a brand name, insulation thickness (in millimeters), insulation material type, cylinder number, and conductor type (suppressor or solid wire). The wire from each spark plug is just long enough to reach the distributor, without excess. Each end of a spark plug wire has a metal terminal that clips onto the spark plug and distributor, coil, or magneto. There are dedicated spark plug wire pliers, tools designed for removing the terminal from a spark plug without damaging it. To reduce radio frequency interference (RFI) produced by the spark being radiated by the wires, which may cause malfunction of sensitive electronic systems in modern vehicles or interfere with the car radio, various means in the spark plug and associated lead have been used over time to reduce the nuisance: # Copper conductors (no suppression) # Resistor in spark plug with copper conductor # Compressed carbon powder as conductor in the lead to act as a resistor # Stainless steel wire wound as a coil in the lead with a resistance of about 1300 ohms/meter since 1980s. This acts as an inductor and a resistor 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「high tension leads」の詳細全文を読む スポンサード リンク
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