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Monday, 18 March 2019

Colour Coding of Resistors

Resistors are made in different sizes and shapes. Some resistors are large enough in size to have their value printed on the body. However there are some resistors that are too small in size to have numbers printed on them. Therefore colour coding is used.


Colour coding is the process in which colours are used to indicate numerical values. The use of bands or stripes is the most common system for colour coding the fixed resistors.

The colour coding for carbon resistors with axial leads is shown in Figure. Moulded carbon resistors have four colour bands printed on one end of the outer casing.
Moulded Carbon Composition Resistor
The colour bands are read from left to right from the end which has the bands closest to it as shown in Figure. The first band indicates the first significant digit and second band indicates second digit while the third band indicates decimal multiplier or number of zeros followed by first two digits. The fourth band indicates the tolerance – the amount by which the actual resistance R can be different from the printed value. Absence of fourth band means the tolerance is ±20%. The table gives the colour code for resisters.

Table - Colour Code:

Colour
Digit
Multiplier
Tolerance
Black
0
100 = 1

Brown
1
101 = 10
±1%
Red
2
102
±2%
Orange
3
103
-
Yellow
4
104
-
Green
5
105

Blue
6
106

Violet
7
107

Gray
8
108

White
9
109

Gold
-
10-1
±5%
Silver
-
10-2
±10%
No colour
-
-
±20%
Pink colour
-
-
High Stability

From the table it can be noted that the darkest colours indicate lowest numbers and lighter colours indicate highest numbers.

The colour coding for wire wound resistors with axial leads is sown in Figure. Note that the first band is double the width for wire wound resistors compared to the rest of the bands. Colour coding is same as that of carbon composition resistors.

Film resistors will have five strips instead of four. In this case the first three bands give first three digits, fourth band gives the multiplier and the fifth band gives the tolerance. These resistors have more precise values with lower tolerance values of ± 0.1 to ± 2 percent.

Resistors below 10Ω will have a third strip of gold or silver which have 0.1 or 0.01 multiplier as shown in Table.

Body End Dot System:

This system is discontinued standard. The numerical values associated with each colour are the same as that of the axial lead resistors.

In these resistors body colour indicates the first digit, one tip colour indicates the second digit, dot colour indicates the number of zeroes or the multiplier and the other tip indicates the tolerance if any.


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