“Resistance is useless.”Hitchhiker’s Guide To The Galaxy
Resistors are a necessary part of any electrical system. They provide the ability to limit current and signal flow, among many other uses. There are numerous different types of resistors, all varying in size and power, but we’re going to take a closer look at arguably the most common type- axial resistors.
Axial resistors are pretty easily recognizable, even to people who know little about electronics. Chances are you’ve seen these tiny little dumbbell-shaped components around. You may have also noticed a lot of them have different colored bands going around them. These colors actually indicate just how much resistance each little guy can provide.
Below is a table that shows every value of each color used in the International Electrotechnical Commision’s standard color-coding system. The colors all have different attributes depending on their position around the resistor.
Reading these colors may seem like a daunting task at first glance, but it’s actually simple enough for just about anyone to figure out. The first thing to look out for is how many bands the resistor has. It can be anywhere from 3 to 6. Single-band resistors (also called zero-ohm links) also exist, almost always designated by a single black stripe. They provide essentially no resistance and are mostly used for bridging gaps, not as actual resistors.
Keep in mind that after you identify a resistor, it doesn’t matter what orientation you install it in. Axial resistors have no polarity.
3- and 4-Band Resistors
Three- and four-band are the most common types of axial resistors. For three-band, the first two colors represent two-digit numerals. The third band indicates the mathematical power of those two numerals. Four-band resistors are the same, with the fourth color representing tolerance (electrical “wiggle room,” indicated by a plus-or-minus percentage of total resistance). Three-band resistors generally have a tolerance of +/- 20%.
It’s important to make sure that you are reading the resistor from left to right. There are two simple ways to make sure you are reading your resistor the correct way. The first and simplest is if it has a pink, silver, or gold band, that is your right side. If you take a look at the table above, you’ll notice that pink, silver, and gold have no numerical values, therefor they will never be the first bands. The second method is to look for uneven spacing of the bands. If one end has three or four bands grouped up tighter than the others, that will be your left side.
Using the example above, we see the bands are red, red, orange, gold. Since gold is present, we know this is the correct reading order. Red, red translates to 22 and orange gives us a multiplier of 1000, meaning the value of these particular resistors is 22,000 ohms with a tolerance of +/- 5%.
5- and 6-Band Resistors
Now that you know how three- and four-band resistors work, you should grasp five-and six-bands pretty quickly. A five-band resistor is exactly like a four-band, only with three numerical bands instead of two, allowing for more precise resistance values. In the example below, we have brown, black, black, silver, brown. You can see that the first three bands are grouped slightly closer together than the last two, which means we’re reading it the correct way. Brown, black, black is 100, and our silver gives us a multiplier of 0.01. That means we have a resistance value of 1 ohm with +/- 1% tolerance.
Six-band resistors are just like five-band, but the final band represents a new category- the temperature coefficient. This value indicates the amount of change in resistance relative to increasing or decreasing temperatures. The values are given in ppm/K (parts-per-notation/degrees Kelvin). Chances are you won’t see too may six-band resistors doing relatively simple home projects, so you shouldn’t worry too much about them unless you’re going to have some intense temperature fluctuations.
And that’s all there is to reading axial resistors! You truly don’t need an engineering degree to dive into electronics. All you really need is a mathematical mind and a little bit of research!