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An alternative method of marking small components is to print 3 digits on them: 2 value digits followed by the power of ten multiplier. Thus the value of a resistor marked 472 is 4,700 ohms; a capacitor marked 104 is 100 nF (100,000 pF). This can be confusing; a resistor marked "472" could in principle be a 472 ohm unit, and we must rely upon experience to interpret markings. It is sometime not obvious whether a colour coded component is a resistor, capacitor, or inductor, and this must be deduced by knowledge of its circuit function, or by measurement (capacitors have infinite resistance; unfortunately, so do faulty open-circuit resistors). Color codes are also used to identify individual wires in a multi-wire cable, particularly for telephone and digital cables. It is simple to identify both ends of a wire by its colour coding. Cable marking is not restricted to single colours. Typically, solid blue, say, may be used for one live conductor, while blue and white stripes may be used for the related earth return which forms a twisted pair with it. ==Resistors, capacitors and inductors= Resistor values are always coded in ohms, capacitors in Picofarads (pF), and inductors in Microhenries (µH). band A is first significant figure of component value band B is the second significant figure band C is the decimal multiplier band D if present, indicates tolerance of value in percent (no color means 20%) For example, a resistor with bands of '' yellow, violet, red, and gold '' will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%. Resistors manufactured for military use may also include a fifth band which indicates component failure rate ( Reliability ); refer to MIL-STD-199 for further details. Tight tolerance resistors may have three bands for significant figures rather than two, and/or an additional band indicating Temperature Coefficient . All coded components will have at least two value bands and a multiplier; other bands are optional (italicised below). The Standard EIA Color Code Table per EIA-RS-279 is as follows: Resistors]] A useful Mnemonic for remembering the first ten color codes is
Historically, mnemonics reflected the attitudes of the times, and raciness assisted memorability. Technicians in New Jersey as late as the seventies could be heard teaching the tasteless
A more staid memory aide is the fact that the central part of the code follows the Color Spectrum . SEE ALSO
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