Page 17 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

The first two colour bands indicate the first two digits in the numeric value of resistance. The third colour band
indicates the multiplier. The first two digits are multiplied by the multiplier to obtain the actual resistance value.
The forth colour band indicates the tolerance in percentage.
Example

Resistance value : If the colour band on a resistor are in the order- Red, Violet, Orange and Gold, then the value
of the resistor is 27,000 ohms with +5% tolerance.

First Second Third Fourth
colour colour colour colour
Red Violet Orange Gold
2 7 1000(10 ) ±5%
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Tolerance value: The fourth band (tolerance) indicates the resistance range within which is the actual value falls.
In the above example, the tolerance is ±5%. ±5% of 27000 is 1350 ohms. Therefore, the value of the resistor
is any value between 25650 ohms and 28350 ohms. The resistors with lower value of tolerance (precision) are
costlier than normal value of resistors.
For less than ten ohms, the third band will be either golden or silver.
The colours are,
Gold - 10-1 = 1/10 = 0.1
Silver - 10-2 = 1/100 = 0.01
Example (Refer Fig 9)
Fig 9

Colour of Colour of Colour of
1st Band 2nd Band 3rd Band
Orange White Gold
3 9 1/10
thus, the value of resistor is 39/10 or 3.9 ohms.
Large value resistances are expressed in kilo ohms and megohms. Letter ‘k’ stands for kilo and M stands for
mega. One kilo equals 1000 (103) and one mega equals 1000000 (106). The resistance values are expressed
as

1000 ohms = 1 k
1800 ohms = 1k 8
100 ohms = 0.1 k
10000 ohms = 0.1 M
1500000 ohms = 1 M 5.

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CITS : Power - Electrician & Wireman - Lesson 60-69