Electronic color code

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Electronic color codes are used to indicate the values or ratings of electronic components, very commomly for resistors, but also for capacitors, inductors, and others. The advantage of colour coding is that essential information can be marked on physically small components of cylindrical or similar shape without the need to read tiny, easily rubbed off, printing. Most low-power resistors are of suitable size and shape; capacitors and inductors less often so. Where space is available, information on value, tolerance, etc. is usually printed on components instead of colour-coding.

An alternative method of marking small components is to print 3 digits on them: 2 value digits followed by the power of ten multiplier. Thus the value of a resistor marked 472 is 4,700 ohms; a capacitor marked 104 is 100 nF (100,000 pF). This can be confusing; a resistor marked "472" could in principle be a 472 ohm unit, and we must rely upon experience to interpret markings.

It is sometime not obvious whether a colour coded component is a resistor, capacitor, or inductor, and this must be deduced by knowledge of its circuit function, or by measurement (capacitors have infinite resistance; unfortunately, so do faulty open-circuit resistors).

Color codes are also used to identify individual wires in a multi-wire cable, particularly for telephone and digital cables. It is simple to identify both ends of a wire by its colour coding. Cable marking is not restricted to single colours. Typically, solid blue, say, may be used for one live conductor, while blue and white stripes may be used for the related earth return which forms a twisted pair with it.

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Resistors, capacitors, and inductors

Image:Resistor bands.png

Resistor values are always coded in ohms, capacitors in picofarads (pF), and inductors in microhenries (µH).

band A is first significant figure of component value
band B is the second significant figure
band C is the decimal multiplier
band D if present, indicates tolerance of value in percent (no color means 20%)

For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%.

Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer to MIL-STD-199 for further details.

Tight tolerance resistors may have three bands for significant figures rather than two, and/or an additional band indicating temperature coefficient.

All coded components will have at least two value bands and a multiplier; other bands are optional (italicised below).

The Standard EIA Color Code Table per EIA-RS-279 is as follows:

Color	Value digit 1	Value digit 2	Value digit 3	Multiplier	Tolerance	Temp. Coefficient
Black	0	0	0	×10⁰
Brown	1	1	1	×10¹	±1% (F)	100 ppm
Red	2	2	2	×10²	±2% (G)	50 ppm
Orange	3	3	3	×10³		15 ppm
Yellow	4	4	4	×10⁴		25 ppm
Green	5	5	5	×10⁵	±0.5% (D)
Blue	6	6	6	×10⁶	±0.25% (C)
Violet	7	7	7	×10⁷	±0.1% (B)
Gray	8	8	8	×10⁸	±0.05% (A)
White	9	9	9	×10⁹
Gold				×0.1	±5% (J)
Silver				×0.01	±10% (K)
None					±20% (M)

Image:Resistors-photo.JPG Image:Condensators.JPG

A useful mnemonic for remembering the first ten color codes is

Better Be Right Or Your Great Big Venture Goes West

where the first letter matches the first letter of the color code, by order of increasing magnitude. An alternative mnemonic is

Bad Beer Rots Our Young Guts, But Vodka Goes Well

Historically, mnemonics reflected the attitudes of the times, and raciness assisted memorability. Technicians in New JerseyTemplate:Fact as late as the seventies could be heard teaching the tasteless