A Short Thread On Colour Code For Carbon Resistors

A closed path or loop made up of electrical components that allow electrons to flow through them is known as an electric circuit. The main components of an electric circuit are transistors, resistors, inductors, capacitors, and diodes. We can connect these components through an electric wire. By the end of this article, you will be able to explain the colour code for carbon resistors and get a coherent answer to your question, ‘how to remember the colour code for carbon resistors’.

A resistor is an electrical component limiting or regulating electric current flow in an electrical circuit. There are many different resistors – carbon composition resistor, thermistor, carbon film resistor, etc. A carbon resistor is a very common resistor. They are easy to operate or inset in an electrical circuit. We can know their resistivity from the colour code for carbon resistors. 

Carbon Resistor

The primary component present in most electrical gadgets is a carbon resistor. It limits the flow of current in the circuits. Carbon resistors have been in use for a long time.

• By definition, a Carbon Resistor is a resistor that comprises small carbon fragments with a cylindrical shaped binder and terminal lead on the other end.

• Carbon Resistors are widely popular over their Tungsten, Platinum, Brass, or Nichrome counterparts due to their resistance capabilities to withstand higher-energy pulses. They are relatively inexpensive, compact, and can be directly installed on circuit boards.

• Carbon Resistors can withstand temperatures of up to 350°C and voltages of up to 15KV.

Composition Of A Carbon Resistor

The main components of a Carbon Resistor are as follows:

• A Ceramic Core

• Carbon Film over the Ceramic Core

• Nickel Caps on both ends

• Lead over both the Nickel Caps for insulation

• A protective epoxy layer over the Resistor

The method used to create this Carbon Resistor is called ‘The Deposition Method’, where pure graphite (carbon) is placed on the ceramic body of the resistor. This inhibits the resistor from tolerating high electric current without being damaged.

Colour Code For Carbon Resistors

Pertaining to the tiny size of the Carbon Resistors, the Radio Manufacturers Association (RMA) invented the Resistor Colour Codes in the 1920s.

They introduced this technique of coding the value of resistance through colour bands because it was very difficult to print the actual resistance value on the tiny Carbon Resistors.

• The power rating of any leaded resistor is specified by a number of colour bands, which collectively determine the value of resistance, tolerance, and dependability rates.

• There might be three to six colour bands on a resistor.

Method To Read The Colour Bands

If you hold a Carbon Resistor horizontally, you will notice some colour bands grouped together on one end and another metallic (gold or silver) band on the other side. Hold the section with grouped colour bands to your left, as resistors are always read from left to right.

• The first two bands indicate the value of resistance in Ohms.

• The third band denotes the decimal multiplier.

• The fourth metallic band represents the tolerance of the resistor at 10% or 5%.

• If there is no fourth band, the tolerance is assumed to be 20%.

Colour Code For Carbon Resistors: Table

In order to understand the Colour Codes, let us go through this table:

Now, let’s take an example to understand this concept better.

You came across a Carbon Resistor with four colour bands (Yellow, Violet, Orange, and Gold) on it. Hold the resistor with the colours Yellow, Violet, and Orange to your left.

• As we know, the first two bands of the resistor represent the first and second significant numbers, which are Yellow and Violet. As per the table mentioned above, they hold the value ‘4’ and ‘7’, respectively.

• The third band denotes the multiplier value, which would be 10³ for the Orange band.

•  The last band represents tolerance or % error in the result; for the Gold band, this value is ±5%.

Now, as per the given information, let’s try to figure out the Resistance Value for this Carbon Resistor:

Resistor Nominal Value would be: First value (4), Second value (7) * Multiplier value of third band (10³), i.e.,

47*10³= 47000 Ω or 47kΩ with a tolerance of ±5%

Similarly, we can easily decode the value of resistance containing different coloured bands with the help of the table mentioned above.

The question arises of memorising the table as it holds importance for determining the values. 

Remembering The Colour Code For Carbon Resistors

Mugging up an entire table is very cumbersome for all of us. 

Luckily, scientists had given us some respite when they introduced a way of remembering these codes in a more fun way.

• You can remember these codes with the help of the phrase, “BB ROY of Great Britain had a Very Good Wife.”

The letters in the upper case represent the first letter of the colours and their position, i.e., Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Grey, and White.

Conclusion

We now know what a Carbon Resistor is, what it is made up of, and how it is beneficial to its other counterparts. We also discussed the colour code for the carbon resistor and calculated the resistance value with these codes. We now know the easy trick of remembering the colour code for carbon resistors.

NOTE: You could come across a carbon resistor with five or six colour bands. These are generally high precision resistors with a different colour band that indicates a third significant digit.

In this scenario, the third colour band becomes an additional digit to the first and second colour bands. The fourth colour band becomes the multiplier in this case, and the fifth colour band denotes tolerance.