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  • Writer's picturePaul W Abernathy, CMECP®

Basic Electrical Math for Electricians - Part 1

Updated: Apr 5, 2021

Having a basic foundation of math skills is vital to being a successful electrician in today's competitive market. Being able to understand the principles of working with decimals, fractions, percentages, squares, and square roots are the basics all electricians should master. It may even come down to picking the right calculator to use on your electrical exam and during your electrical exam preparation.

The first step in your success plan, yes we are always going to be positive and tell you it is a SUCCESS PLAN because we believe in your success and that it is imminent, would be to select the proper calculator. You want a calculator that is dual powered, meaning it has both solar and battery power sources just in case something happens during that critical study moment. There are many on the market so make sure it is one that is easy to read, easy to use, and one that you will keep with you habitually while studying.

Let's start this first lesson by learning how to work with decimals. In most cases, you will want to carry out the calculations to just two or even three numbers behind a decimal point. In our examples, we will always carry it out to four points beyond the decimal so that you have a variety of options. Any number that is .5 and above will be rounded up and number .4 or less will be dropped in our examples.

Let's take .716 as our first value. Because the 6 is more than 5, the 1 can be rounded up to 2 to create .72. As you see, once we round up the 6 will technically drop off reducing our placements from three to two after the decimal point. How about this next example.

Let's take 15.72 as our next example. Because the 2 is less than 5 it can be dropped resulting in 15.7. Once again dropping from two positions to only one after the decimal point. Fairly simply right?

It is very important in electrical math to be able to add, subtract, multiply, and divide various numbers that are configured as decimals. So let's work on a few examples so that we are all clear on how to work decimals. Be sure to align the decimals properly or you may struggle with the solution.

Example # 1: 484.773 + 12.667 = 497.44

Solution: In the 448.773 it was changed to 484.77, dropping the 3 and in the 12.667, the second 6 was increased to 7 and the 7 at the end was dropped since it was above 5 so it was rounded up.

Example # 2: 2461 - 237.8642 = 2223.1358

Solution: You add 4 zeros after 2461 so that it is now 2461.0000 and you subtract that, lining up the decimal point of course, by 237.8642. Now, below is what you have when you follow the principles of subtraction.

Example # 3: 0.481 x 0.400 = 0.1924

Solution: The best way to work decimals with multiple spaces is to forget the decimal point and simply work the numbers as whole numbers. For example, 481 x 400, and once we are done then we can add the decimals. In our case, there are 6 decimal places, three in each value. Start at the end and move the decimal six places to the left, then drop the 2 last zeros.

Example # 4: 9.152 ÷ 0.8 = 11.44

Solution: The first thing we need to do is move the decimal one places to the right on both values in our example. You should always turn the value to the left into a whole number, such as in our example 0.8 to 8. The 8. is the divisor and 91.52 is our dividend.

Once the decimals are moved we can work the equation as you would a normal division problem.

As you can see working with decimals isn't that difficult if you stop and think about the equation. You most certainly will have a situation where you will need to do come addition, subtraction, multiplication, and division on decimals in your career as an electrician so hopefully this was helpful.

This is Part 1 of 4 in a series on basic electrical math calculations. Join us in the next edition where we work with fractions.

Until then if you are interested in learning more about electrical exam preparation to help you pass your electrical exam, check out our Fast Trax™ NEC Learning System at for more information.

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