History and Standardization
– RMA resistor color code guide developed by the Radio Manufacturers Association (RMA)
– First radios with RMA color-coded resistors built in 1930
– Name variations of the code over 93 years (RMA, RTMA, RETMA, EIA)
– Standardized in IEC 62:1952 by the International Electrotechnical Commission (IEC)
– Extended to cover capacitors with IEC 62:1968
Resistors
– E12 series with twelve preferred values per decade
– 0Ω resistor (zero ohm) marked with a single black band
– Color band system used to indicate component value and tolerance
– Precision resistors may have a five band system for added accuracy
– Resistors for military use may include a fifth band indicating component failure rate
Color Band System
– First significant figure of component value indicated by the first band
– Second significant figure indicated by the second band
– Decimal multiplier indicated by the third band
– Tolerance of value in percent indicated by the fourth band
– Precision resistors may have an extra-wide first band or additional bands for temperature coefficient of resistance
Capacitors
– Capacitors may be marked with 4 or more colored bands or dots
– Colors encode the first and second most significant digits of the value in picofarads
– Third color represents the decimal multiplier
– Additional bands may have varying meanings
– Low-tolerance capacitors may have the first 3 digits of the value marked
Other Components
– Inductors: Manufacturers of small inductors use the resistor color code system
– Diodes: Small JEDEC 1N-coded diodes are sometimes encoded using the standard color code
– Wire: Wires may be color-coded to identify their function, voltage class, polarity, phase, or circuit
– Transformer: Power transformers used in North American vacuum-tube equipment were color-coded to identify leads Source: https://en.wikipedia.org/wiki/Electronic_color_code
An electronic color code or electronic colour code (see spelling differences) is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunications cables. Different codes are used for wire leads on devices such as transformers or in building wiring.
