Electronic color code
RMA (Radio Manufacturers Association) Resistor Color Code Guide, ca. 1945–1955.
A 100 kΩ, 5% axial-lead resistor
The electronic color code is used to indicate the values or ratings of electronic components, usually for resistors, but also forcapacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunicationscables.
The electronic color code was developed in the early 1920s by the Radio Manufacturers Association (RMA), later the Radio Electronics Television Manufacturers' Association(RETMA), now part of the Electronic Industries Alliance (EIA)[1] Therefore, the code was known as RMA, RTMA, RETMA or EIA color code. In 1952, it was standardized in IEC 62:1952 by the International Electrotechnical Commission (IEC) and since 1963 also published as EIA RS-279.[2] Originally only meant to be used for fixed resistors, the color code was extended to also cover capacitors with IEC 62:1968. 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 isIEC 60062:2016[3] and EN 60062:2016.
(In addition to the color code, these standards also define a letter and digit code for resistors and capacitors.)
Colorbands 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 practical on small components. Where passive components come in surface mountpackages, their values are identified with printed alphanumeric codes instead of a color code.
Resistor color-coding
A 2260 Ω, 1% precision resistor with 5 color bands (E96 series), from top 2-2-6-1-1; the last two brown bands indicate the multiplier (×10), and the 1% tolerance. The larger gap before the tolerance band is somewhat difficult to distinguish.
To distinguish left from right there is a gap between the C and D bands.
- band A is the first significant figure of component value (left side)
- band B is the second significant figure (some precision resistors have a third significant figure, and thus five bands).
- band C is the decimal multiplier
- band D if present, indicates tolerance of value in percent (no band means 20%)
For example, a resistor with bands of yellow, violet, red, and gold has first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4465and 4935 ohms.
Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer toMIL-HDBK-199[4] for further details.
Tight tolerance resistors may have three bands for significant figures rather than two, or an additional band indicating temperature coefficient, in units of ppm/K.
All coded components have at least two value bands and a multiplier; other bands are optional.
The standard color code per IEC 60062:2016is as follows:
One decade of the E12 series (there are twelve preferred values per decade of values) shown with their electronic color codes on resistors
A 0 Ω resistor, marked with a single black band
Resistors use preferred numbers for their specific values, which are determined by theirtolerance. These values repeat for every decade of magnitude: 6.8, 68, 680, and so forth. In the E24 series the values are related by the 24th root of 10, while E12 series are related by the 12th root of 10, and E6 series by the sixth root of 10. The tolerance of device values is arranged so that every value corresponds to a preferred number, within the required tolerance.
Zero ohm resistors are made as lengths of wire wrapped in a resistor-shaped body which can be substituted for another resistor value in automatic insertion equipment. They are marked with a single black band.[7]
The 'body-end-dot' or 'body-tip-spot' system was used for radial-lead (and other cylindrical) composition resistors sometimes still found in very old equipment; the first band was given by the body color, the second band by the color of the end of the resistor, and the multiplier by a dot or band around the middle of the resistor. The other end of the resistor was colored gold or silver to give the tolerance, otherwise it was 20%.[8][9][10][11]
Capacitor color-coding
Capacitors may be marked with 4 or more colored bands or dots. The colors encode the first and second most significant digits of the value, and the third color the decimal multiplier in picofarads. Additional bands have meanings which may vary from one type to another. Low-tolerance capacitors may begin with the first 3 (rather than 2) digits of the value. It is usually, but not always, possible to work out what scheme is used by the particular colors used. Cylindrical capacitors marked with bands may look likeresistors.
Extra bands on ceramic capacitors identify the voltage rating class and temperature coefficient characteristics.[8] 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.
Inductor color-coding
IEC 60062 / EN 60062 don't define a color code for inductances, but various manufacturers of inductors utilize the resistor color code for this purpose.[12] A white tolerance ring may indicate custom specifications.[12]
Diode part number
The part number for diodes is sometimes also encoded as colored rings around the diode, using the same numerals as for other parts. The JEDEC "1N" prefix was assumed, and the balance of the part number was given by three or four rings. The 1N4148 would then be color coded as yellow (4), brown (1), yellow (4), grey (8).
Postage stamp capacitors and war standard coding
Postage-stamp mica capacitorsmarked with the EIA 3-dot and 6-dot color codes, giving capacitance value, tolerance, working voltage, and temperature characteristic. This style of capacitor was used in vacuum-tube equipment.
Capacitors of the rectangular "postage stamp" form made for military use during World War II used American War Standard(AWS) or Joint Army Navy (JAN) coding in six dots stamped on the capacitor. An arrow on the top row of dots pointed to the right, indicating the reading order. From left to right the top dots were: either black, indicating JANmica, or silver, indicating AWS paper; first significant digit; and second significant digit. The bottom three dots indicated temperature characteristic, tolerance, and decimal multiplier. The characteristic was black for±1000 ppm/°C, brown for ±500, red for ±200, orange for ±100, yellow for −20 to +100 ppm/°C, and green for 0 to +70 ppm/°C.
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.[13]
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