Product Code Database
An electronic color code or electronic colour code (see spelling differences) is used to indicate the values or ratings of electronic components, usually for , but also for , , 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.
In the 1920s, the RMA resistor color code was developed by the Radio Manufacturers Association (RMA) as a fixed resistor coloring code marking. In 1930, the first Radio receiver with RMA color-coded resistors were built. Over many decades, as the organization name changed (RMA, RTMA, RETMA, EIA) so was the name of the code. Though known most recently as EIA color code, the four name variations are found in books, magazines, catalogs, and other documents over more than years.
In 1952, it was standardized in by the International Electrotechnical Commission (IEC) and since 1963 also published as EIA RS-279. Originally only meant to be used for fixed resistors, the color code was extended to also cover capacitors with . The code was adopted by many national standards like DIN 40825 (1973), BS 1852 (1974) and IS 8186 (1976). The current international standard defining marking codes for resistors and capacitors is . In addition to the color code, these standards define a letter and digit code named RKM code for resistors and capacitors.
Color bands were used because they were easily and cheaply printed on tiny components. However, there were drawbacks, especially for color blind people. Overheating of a component or dirt accumulation may make it impossible to distinguish brown from red or orange. Advances in printing technology have now made printed numbers more practical on small components. The values of components in surface mount packages are marked with printed alphanumeric codes instead of a color code.
In the above example, a resistor with bands of red, violet, green, and gold has first digit 2 (red; see table below), second digit 7 (violet), followed by 5 (green) zeroes: . Gold signifies that the tolerance is ±5%.
Precision resistors may be marked with a five band system, to include three significant digits, a power of 10 multiplier (number of trailing zeroes, and a tolerance band. An extra-wide first band indicates a wire-wound resistor. Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer to MIL-HDBK-199 for further details.
Tight tolerance resistors may have three bands for significant figures rather than two, or an additional band indicating temperature coefficient of resistance (TCR), in units of ppm/Kelvin.
All coded components have at least two value bands and a multiplier; other bands are optional.
The standard color code per is as follows:
Resistors use various E series of preferred numbers for their specific values, which are determined by their tolerance. These values repeat for every decade of magnitude: ... 0.68, 6.8, 68, 680, ... For resistors of 20% tolerance the E6 series, with six values: 10, 15, 22, 33, 47, 68, then 100, 150, ... is used; each value is approximately the previous value multiplied by . For 10% tolerance resistors the E12 series, with as multiplier, is used; similar schemes up to E192, for 0.5% or tighter tolerance are used. The separation between the values is related to the tolerance so that adjacent values at the extremes of tolerance approximately just overlap; for example, in the E6 series is 12, while is also 12.
Zero ohm resistors, marked with a single black band, are lengths of wire wrapped in a resistor-like body which can be mounted on a printed-circuit board (PCB) by automatic component-insertion equipment. They are typically used on PCBs as insulating "bridges" where two tracks would otherwise cross, or as soldered-in jumper wires for setting configurations.
The physical size of a resistor is indicative of the power it can dissipate.
There is an important difference between the use of three and of four bands to indicate resistance. The same resistance is encoded by:
The colors are sorted in ascending order of visible light photon frequency/energy like in a rainbow to make them easy to remember and to reduce the significance of possible read errors due to color shifts and fading over time: red (2), orange (3), yellow (4), green (5), blue (6), violet (7). Black (0) has no energy, brown (1) has a little more, white (9) has everything and grey (8) is like white, but less intense.
Extra bands on ceramic capacitors identify the voltage rating class and temperature coefficient characteristics. A broad black band was applied to some tubular paper capacitors to indicate the end that had the outer electrode; this allowed this end to be connected to chassis ground to provide some shielding against hum and noise pickup.
Polyester Film capacitor and "gum drop" tantalum electrolytic capacitors may also be color-coded to give the value, working voltage and tolerance.
A similar six-dot code by EIA had the top row as first, second and third significant digits and the bottom row as voltage rating (in hundreds of volts; no color indicated 500 volts), tolerance, and multiplier. A three-dot EIA code was used for 500 volt 20% tolerance capacitors, and the dots signified first and second significant digits and the multiplier. Such capacitors were common in vacuum tube equipment and in surplus for a generation after the war but are unavailable now.
Audio transformers for vacuum tube equipment were coded blue for the finishing lead of the primary, red for the B+ lead of the primary, brown for a primary center tap, green for the finishing lead of the secondary, black for grid lead of the secondary, and yellow for a tapped secondary. Each lead had a different color since relative polarity or phase was more important for these transformers. Intermediate-frequency tuned transformers were coded blue and red for the primary and green and black for the secondary.
Building wiring under the US National Electrical Code and the Canadian Electrical Code is identified by colors to show energized, neutral, and grounding conductors, and to identify phases. Other color codes are used in the UK and other areas to identify building wiring or flexible cable wiring.
Mains electrical wiring, both in a building and on equipment, was once usually red for live, black for neutral, and green for earth, but this was changed as it was a hazard for color-blind people, who might confuse red and green; different countries use different conventions. Red and black are frequently used for positive and negative of battery or other single-voltage DC wiring.
Thermocouple wires and extension cables are identified by color code for the type of thermocouple; interchanging thermocouples with unsuitable extension wires destroys the accuracy of the measurement.
Automotive wiring is color-coded but standards vary by manufacturer; differing SAE and DIN standards exist.
Modern personal computer peripheral cables and connectors are color-coded to simplify connection of speakers, microphones, mice, keyboards and other peripherals, usually according to coloring schemes following recommendations such as PC System Design Guide, PoweredUSB, ATX, etc.
A common convention for wiring systems in industrial buildings is: black jacket – AC less than , blue jacket – DC or communications, orange jacket – medium voltage or , red jacket or higher. Red-jacketed cable is also used for relatively low-voltage fire alarm wiring, but has a much different appearance.
Local area network cables may also have non-standardised jacket colors identifying, for example, process control network vs. office automation networks, or to identify redundant network connections, but these codes vary by organization and facility.
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