Colour Code for Resistors: We know that the resistance value, tolerance, and wattage rating are the main specification of resistors. They are generally printed onto its body as numbers or letters when the body of the resistor has a large surface area to read the print, such as large power resistors. But these specifications must be shown in another manner when the resistor is little like a 14 watt carbon or film type because the print would be too small to read. So to overcome this problem, coloured bands are printed on small resistors to indicate both their resistive value and their tolerance, with the physical size of the resistor indicating its wattage rating. These coloured painted bands produce a system of identification generally known as a Resistor Colour Code.

Resistors and their Types

A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors are generally of the following two major types:-
1. Wire Bound Resistors
2. Carbon Resistors

1. Wire Bound Resistors:- It is made by winding the wires of an alloy like nichrome, manganin, or constantan, etc. Materials are so chosen such that their resistivities are relatively less sensitive to temperature.

2. Carbon Resistors:- In carbon resistors, carbon with a suitable binding agent is moulded into a cylinder. Wire leads have connected the resistor to a circuit. Carbon resistors are compact and inexpensive. Hence, colour codes are used to give their significant values.

Resistor Colour Code

Resistor colour code is one of the electronic colour codes used to know the values of leaded resistors. This type of electronic colour code was used for years, and even today, resistor colour codes are considered to be the best and appropriate method. Usually, printing the values of the resistors in figures is not a good method since it will get erased during the handling process. So we make use of the resistor colour codes chart to determine the value of the resistors. Higher range resistors are mostly made from carbon. We generally use carbon resistors because they are compact, less expensive, hence it is used extensively in electronic circuits.

Colour Codes are used to give values to the carbon resistors because they are small in size. So, printing these numbers on large electronic components can be easy, but resistors are usually very tiny, and it is challenging to print resistance values on them. Hence, instead of directly printing the numbers, we print the colour codes or colour bands, and these colour bands represent the electrical resistance value, the tolerance rate, and sometimes the reliability or failure rates. These colour bands are called resistor colour codes. For indicating the value of a resistor, the use of colour bands on the body of a resistor is most common. Electronic Industries Association (EIA) standardized the Colour-coding system.

Resistor Colour Code Chart

The chart below shows how to determine the resistance value and tolerance for resistors. This table can also be used to specify the colour of the bands when the values are known.

How to Remember:- To remember the value of colour coding used for carbon resistor, the blew sentence is found to be of great help (where bold letters stand for colours). It is remembered as B ROY Great Britain Very Good Wife wearing Gold Silver necklace’.

How does Resistor Colour Code Work?

The resistors have a set of co-axial coloured rings on them whose significance is listed in the table of the resistor colour code chart. To get the specification of a resistor, hold the resistor in such a way that bands with smaller gaps should be on your left hand side. The resistor colour code mark is always based on reading one band at a time, starting from the left to the right, with the larger width tolerance band oriented to the right side, indicating its tolerance. For example, In the 4-band resistor, The first two bands from the left end indicate the first two significant figures of the resistance in ohms. The third band indicates the decimal multiplier.

The last band represents the tolerance or possible variation in percentage about the indicated values. Each digit of the resistor’s value is represented by the set of individual coloured rings or bands in spectral order. The first digit is identified by matching the colour of the first band with its associated number within the digit column from the colour chart, and this represents the first digit of the resistance value. Similarly,  the second digit is identified by matching the colour of the second band with its associated number in the digit column of the colour chart. Hence finally, after writing all the digits in sequence and by using multiplier, we get the resistance value and so on.

Reading Resistor Codes

These are tips given to read the colour code:

1. To read them, hold the resistor such that the tolerance band is on your right. The tolerance band is placed a little further away from the other bands, and its colour is generally gold or silver.
2. The reading direction might not always be clear. Sometimes, the reading direction can be obtained by the increased space between bands 3 and 4. As the gold or silver band (the tolerance) is always the last band
3. Starting from your left, note down all the colours of the bands and write them down in sequence.
4. Next, use the resistor colour code chart to see which digits they represent and get their values.

Examples

Reading a typical \(4-\)band, \(5-\)band, and \(6-\)band resistor:-

\(4-\)Band Resistor: The four-band colour code variation is mostly used. In these resistors, the first two bands represent the resistance value, the next one for the multiplier, and the last one for the tolerance. In the example given below, from the left, these bands are green, blue, red, and gold. By using the colour code chart, we have:

(a) 4- Band Resistor

The colours are noted from left to right.
Colour \(1 →\) Green \(→\) First significant figure \(→ 5\)
Colour \(2 →\) Blue \(→\) Second significant figure \(→ 6\)
Colour \(3 →\) Red \(→\) Decimal multiplier \(→ 100\)
Colour \(4 →\) Golden \(→\) Tolerance or possible variation in percentage \(→ ± 5\%\)
\(R = (56 × 10^2 ± 5\%)\)
\(R = (5600 ± 5\%)\)
The resistance value, therefore, lies between \(5320\,\rm{Ω}\) and \(5880\,\rm{Ω}\).

\(5-\)Band Resistor: Resistors with high precision have an extra band to indicate a third significant digit. Therefore, the first three bands indicate the significant digits, the fourth band represents the multiplying factor, and the fifth band represents the tolerance. In example (b), we have:

(b) 5- Band Resistor

The colours are noted from left to right :
Colour \(1 →\) Brown \(→\) First significant figure \(→ 1\)
Colour \(2 →\) Yellow \(→\) Second significant figure \(→ 4\)
Colour \(3 →\) Purple \(→\) Second significant figure \(→ 7\)
Colour \(4 →\) Black \(→\) Decimal multiplier \(→ 1\)
Colour \(5 →\) Green \(→\) Tolerance or possible variation in percentage \(→ 0.5\%\)
\(R = (147 × 1 ± 0.5\%)\)
\(R = (147 ± 0.5\%)\)

\(6-\)Band Resistor: The first three colour bands represent significant digits, the fourth band represents the decimal multiplier, the fifth band represents the tolerance, and the sixth band represents the temperature coefficient. Resistors with \(6\) bands are usually for high precision resistors that have an additional band to specify the temperature coefficient \((\rm{ppm/K})\).
From the given figure (c), the colours are noted from left to right we have:

(c) 6- Band Resistor

Colour \(1 →\) Orange \(→\) First significant figure \(→ 3\)
Colour \(2 →\) Red \(→\) Second significant figure \(→ 2\)
Colour \(3 →\) Brown \(→\) Second significant figure \(→ 1\)
Colour \(4 →\) Green \(→\) Decimal multiplier \(→ × 10\)
Colour \(5 →\) Brown \(→\) Tolerance or possible variation in percentage \(→ 1\%\)
Colour \(6 →\) Red \(→\) TCR \(→ 50\,\rm{ppm/K}\)
\(R = (321 × 10 ± 1\%)\)
\(R = (3210 ± 1\%)\)

Colour Code for Resistors – Sample Problems

Q.1. The four colours on a resistor are brown, yellow, green, and gold, as read from left to right. What is resistance corresponding to these colours?

Ans: From the table, we can write that
Brown colour \(→ 1\)
Yellow colour \(→ 4\)
Green colour \(→ 10^5\) and
Gold colour \(→ 5\%\)
Then, we can write the Resistance value as:-
\(R = (14 × 10^5 ± 5\%).\)

Summary

Resistors are the devices that control or limit the flow of current and also provide a voltage drop in electrical circuits. Because carbon resistors are physically small, so it is difficult to print all the resistance values in numbers, that’s why they are colour-coded to identify their resistance and their tolerance value easily in ohms. The resistors have a set of co-axial coloured rings in which the colours are noted from left to right, and then the resistor colour code chart is used to represent the significance of the colours printed on it.

FAQs on Colour Code for Resistors

Q.1. Why are resistors colour-coded?
Ans: Resistors are coded with colours to give the specification of resistors. Coloured bands are used to quickly identify a resistor’s resistive value and its percentage of tolerance.

Q.2. What happens if we use the wrong resistor?
Ans: The equipment will cease to function in short order either by the resistor itself burning up or by the heat; it generates burning up an adjacent component or possibly the circuit board it’s mounted on or even foil pattern on the circuit board or maybe all three.

Q.3. Where do we use resistors in everyday life?
Ans: Resistors are present everywhere in our life. All electronic boards and devices utilize them. It is present in our laptop boards, mobile phone kits, and motherboards, home accessories circuits, and in all SMD resistors. They are also used in kettles, lamps, headphones, and almost all electronic/electrical devices.

Q.4. What is the difference between resistor and resistance?
Ans: Resistance is the property of a conductor, which determines the quantity of current that passes through it when a potential difference is applied across it. And a resistor is an electrical component that has predetermined electrical resistance, like 1 ohm, 10 ohms, 100 ohms, 10000 ohms etc.

Q.5. How does a resistor colour code work?
Ans: The resistor’s bands are made of several colours, which together specify the resistance value, tolerance, and sometimes the reliability rate. Resistors with high precision have five bands. In 5-band resistors, the first three bands indicate the significant digits, the fourth band represents the multiplier, and the fifth band represents the tolerance.