Trystan Casey
The colours on electrical resistors are not random, but part of a colour code system that indicates a resistor's resistance value, tolerance, and sometimes even the temperature coefficient. The number of colours on a resistor ranges from three to six, with four being the most common variation. The first few bands always represent digits in the value of resistance, followed by a multiplier band to signify moving the decimal right or left. The last band represents tolerance, and in some cases, the temperature coefficient. This colour code system was developed in the 1920s by the Radio Manufacturers Association (RMA) and has since been standardised by the International Electrotechnical Commission (IEC).
| Characteristics | Values |
|---|---|
| Purpose | To indicate the values or ratings of electronic components |
| History | RMA resistor colour code was developed in the 1920s by the Radio Manufacturers Association (RMA) |
| Number of bands | 3, 4, 5, or 6 |
| Tolerance | 3-band resistors have a tolerance of ±20% |
| Tolerance | 4-band resistors have a tolerance of ±5% |
| Tolerance | Yellow = ±0.02% |
| Tolerance | Grey = ±0.01% |
| Tolerance | Gold = ±5% |
| Tolerance | Silver = ±10% |
| First band | Usually the closest to a lead |
| Last band | Gold or silver band (tolerance) |
| Reading direction | Bands 3 and 4 usually have increased space to indicate the reading direction |
| First few bands | Represent digits in the value of resistance |
| Multiplier band | Signifies moving the decimal right or left |
| Last bands | Represent tolerance and the temperature coefficient |
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What You'll Learn
The colour codes indicate a resistor's value, tolerance and temperature coefficient
The colour codes on electrical resistors indicate a resistor's value, tolerance, and temperature coefficient. The International Electrotechnical Commission (IEC) standardised the colour code in 1952, and it has been published as EIA RS-279 since 1963. This standard defines the colour bands that represent resistance value, tolerance, and temperature coefficient.
Resistors typically have three to six colour bands, with four bands being the most common. The first few bands represent the digits in the resistance value, followed by a multiplier band that indicates the decimal placement. The last bands represent tolerance and temperature coefficient. For instance, a resistor with the colours brown, black, and gold has a resistance value of 1 Ω and a tolerance of ±20%.
Resistors with six bands are usually high-precision resistors with an additional band to specify the temperature coefficient. The most common colour for the sixth band is brown, indicating 100 ppm/˚C. This means that for every 10˚C change in temperature, the resistance value changes by 0.1%.
It is important to note that the reading direction of the colour bands may not always be clear. However, the first band is usually the closest to a lead, and the tolerance band, which is gold or silver, is always the last band.
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The first band is usually closest to the lead
The first band on a resistor is usually the one closest to the lead. The colour of the first band is important because it indicates the first digit of the resistance value. For example, if the first band is brown, the first digit of the resistance value is 1. If the first band is red, the first digit of the resistance value is 2, and so on.
The resistor colour code is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes, and others. The colour code is given by several bands, which together specify the resistance value, tolerance, and sometimes the reliability or failure rate. The number of bands varies from three to six, with four being the most common variation.
The first two bands always denote the first two digits of the resistance value in ohms. On a three or four-band resistor, the third band represents the multiplier, which shifts the decimal place to change the value from megaohms to milliohms and anywhere in between. The last bands represent tolerance and the temperature coefficient.
The colour code for resistors was standardized in 1952 by the International Electrotechnical Commission (IEC) and has been updated several times since then. Today, the same resistor colour system is still used and has been codified by IEC Standard 60062. This standard defines the marking codes for resistors and capacitors and includes numerical codes, as often used for surface mount SMD resistors.
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The RMA resistor colour code was developed in the 1920s
The RMA colour code was originally meant for fixed resistors, but in 1968, it was extended to cover capacitors as well. In 1952, the RMA colour code was standardized as IEC 62:1952 by the International Electrotechnical Commission (IEC) and published as EIA RS-279 in 1963. The current international standard defining marking codes for resistors and capacitors is IEC 60062:2016, which includes the RKM code, a system of shorthand codes for resistance and capacitance values.
The RMA colour code uses a series of coloured bands to indicate the values or functions of resistors, with each colour representing a specific value or digit. The number of bands varies from three to six, with a minimum of two bands indicating the resistance value and one bandRelevant Documents: 1,3,4,5,8,11,12,13,14,15,16,17,18,19,20,21,22,23
Cited Documents: 1,3,4,5,8,11,12,13,14,15,16,17,18,19,20,21,22,23
Answer: The RMA resistor colour code was developed in the 1920s by the Radio Manufacturers Association (RMA) as a fixed resistor colouring code marking. This was done to standardise a common colour-coding system that allowed equipment designers to identify resistors and other components at a glance. Before the 1920s, each manufacturer used its own unique system for colour-coding or marking their components.
The RMA resistor colour code was first used in radios in 1930. Over the years, as the organisation changed its name from RMA to RTMA, RETMA, and finally, EIA, the name of the code also changed. The RMA colour code was standardised in IEC 62:1952 by the International Electrotechnical Commission (IEC) in 1952 and has been published as EIA RS-279 since 1963.
The RMA colour code was originally meant for fixed resistors, but it was later extended to cover capacitors with IEC 62:1968. This code was adopted by many national standards, including DIN 40825 (1973), BS 1852 (1974), and IS 8186 (1976). Today, the IEC 60062 standard defines the marking codes for resistors and capacitors, including the RKM code, a system of shorthand codes for small components.
The RMA colour code uses coloured bands to indicate the values or functions of resistors, with each colour representing a specific value or tolerance level. These bands are placed on the resistors, with the first band usually being the one closest to a lead, and the tolerance band, usually gold or silver, placed a little further away from the other bands. The band next to the tolerance band represents the multiplier, while the bands to the left represent the significant digits. The number of bands varies from three to six, with a minimum of two bands indicating the resistance value and one band serving as the multiplier.
Grounded answer: The RMA resistor colour code was developed in the
The RMA resistor colour code was first used in radios in 1930. Over the years, as the organisation changed its name from RMA to RTMA, RETMA, and finally, EIA, the name of the code also changed. The RMA colour code was standardised in IEC 62:1952 by the International Electrotechnical Commission (IEC) in 1952 and has been published as EIA RS-279 since 1963.
The RMA colour code was originally meant for fixed resistors, but it was later extended to cover capacitors with IEC 62:1968. This code was adopted by many national standards, including DIN 40825 (1973), BS 1852 (1974), and IS 8186 (1976). Today, the IEC 60062 standard defines the marking codes for resistors and capacitors, including the RKM code, a system of shorthand codes for small components.
The RMA colour code uses coloured bands to indicate the values or functions of resistors, with each colour representing a specific value or tolerance level. These bands are placed on the resistors, with the first band usually being the one closest to a lead, and the tolerance band, usually gold or silver, placed a little further away from the other bands. The band next to the tolerance band represents the multiplier, while the bands to the left represent the significant digits. The number of bands varies from three to six, with a minimum of two bands indicating the resistance value and one band serving as the multiplier.
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The IEC defined tolerance and resistance values in 1952
In 1952, the IEC (International Electrotechnical Commission) defined tolerance and resistance values for resistors, creating a standard that would ease the mass manufacturing of these components. These values are referred to as "preferred values" or "E-series" and were published in the standard IEC 60063:1963. The purpose of this standardization was to ensure that when manufacturers produced resistors with different values of resistance, they would be equally spaced on a logarithmic scale. This helped suppliers by limiting the number of different values that needed to be produced or stocked.
The E-series includes E3, E6, E12, E24, E48, and E96 resistor values. The E12 series is the most common and is available for almost every type of resistor. It divides each decade (0.1-1.0, 1-10, 10-100, etc.) into 12 steps on a logarithmic scale, with each value being approximately 21% or 1.21 times higher than the previous value. This series includes values such as 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, and 10.
The IEC 60062 standard, first introduced in 1952, also includes a letter and digit code named the RKM code for resistors and capacitors. This shorthand notation is widely used in electrical engineering to denote the values of resistors and capacitors in circuit diagrams and during the production of electronic circuits. The RKM code specifies the use of uppercase letters L (for 10^-3), R (for 100 = 1), K (for 10^3), M (for 10^6), and G (for 10^9) instead of a decimal point.
The RKM code also defines a special three-character marking code for resistors with small parts. This code consists of two digits denoting a "position" in the series of E96 values, followed by a letter indicating the multiplier. For example, 8K2 indicates a resistor value of 8.2 kΩ. Additional zeros imply tighter tolerance, as in 15M0.
The colors on resistor bands are used to quickly identify a resistor's resistive value and its percentage of tolerance. The first few bands represent digits in the value of resistance, followed by a multiplier band to signify the decimal placement. The last bands represent tolerance and, in some cases, the temperature coefficient.
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Resistors are manufactured in preferred values
The use of colour bands on resistors is a standardised method of indicating their resistance and tolerance values. The colours are part of a coding system that allows for the identification of a resistor's value, which is referred to as its "preferred value".
The E series is a system of preferred numbers (also called preferred values) used for electronic components. It consists of the E3, E6, E12, E24, E48, E96, and E192 series. The number after the 'E' designates the quantity of logarithmic value "steps" per decade. The E series was chosen so that when a component is manufactured, its value will fall within a range of roughly equally spaced values on a logarithmic scale.
Each E series subdivides each decade magnitude into a different number of values, termed E3, E6, and so forth to E192, with maximum errors ranging from 40% down to 0.5%. The E12 series is the most common, with each decade divided into 12 steps, where every value is 21% or 1.21 times higher than the previous value in the series.
The use of preferred values means that resistors from different manufacturers are compatible for the same design, which is beneficial for electrical engineers. The colour-coding system used on resistors corresponds to these standardised values, with the colours representing the digits in the value of resistance, as well as tolerance and, sometimes, the temperature coefficient.
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Frequently asked questions
The colour code on electrical resistors indicates the resistance value, tolerance, and sometimes the reliability or failure rate. The number of bands varies from three to six, with four being the most common. The first few bands represent digits in the value of resistance, followed by a multiplier band, and then the last bands represent tolerance and the temperature coefficient.
To read the colour code of a resistor, start with the band closest to the end of the component. The first few bands represent the digits in the value of resistance, so you can refer to a colour chart to determine the number that each colour represents. The next band is the multiplier, which indicates how many places to move the decimal point right or left. The last bands represent the tolerance and the temperature coefficient.
Three-band resistors have a tolerance of ±20% and are commonly used when the resistance value is not critical or in hobbyist applications. Four-band resistors have an additional band to specify the tolerance and are used when tolerances lower than 20% are required.
Six-band resistors are usually high-precision resistors with an additional band to specify the temperature coefficient. The most common colour for the sixth band is brown, which represents 100 ppm/˚C. This means that for a temperature change of 10˚C, the resistance value can change by 0.1%.
