Within a few months of taking a position as a trainee electrical estimator, I was sent to training courses. The classes and teachers were great. I learned a lot in the beginner and advanced classes. Unfortunately, there is only so much they teach you in the classroom’s limited time. Your education will continue at the school of hard knocks for as long as you remain an electrical estimator.

Hopefully, this article can help keep some of those lessons from hurting so much. And just so you are not confused, I took these classes in the very early 1980s, slightly before computers and digital tools became popular. You may feel like you don’t need to know the background, but it helps to know where you came from. Even though these tools are a part of everyday life now, they will keep evolving and become part of your ongoing education.

Scales

The first subject I want to talk about is scales. Although this is very basic, I want to be sure everyone reading this understands drawing scales. Scales on a paper blueprint (electrical drawing) are a proportional ratio that translates paper measurements into actual real-world dimensions. An example would be ¼ inch = 1 foot, which translates to ¼ inch on a drawing equals 1 foot in the real world. We use measuring devices to scale the plans to derive total real-world distances.

Measuring tools

I was presented with a Minerva mechanical measuring device when I enrolled in the classes. Soon after, the Minerva was replaced with digital measuring devices. Two brands I am familiar with are Scale Master and Scalex. These tools are used to measure distance on a paper electrical drawing. If you are doing your takeoff with an on-screen product, these scales are built into the software, along with tools for making measurements.

Multiple scales

Dealing with multiple scales is one of the first problems I encountered. Scales can change from plan sheet to plan sheet. This affected my measurements of feeders that spanned more than one plan sheet. 

My solution to this problem was to measure the first plan sheet, record the distance, reset my scaling device to the correct scale, and then measure the next plan sheet. When the measurements were completed, I added all of them together and recorded the total distance. This was not that difficult. However, the bigger problem would have been missing the fact that the scale was changing with each plan sheet. Scales can even change between details on the same plan sheet.

Incorrect scales

Plans with inaccurate scales started becoming a problem for me a little over 20 years ago. A building I knew to be 100 feet wide was scaling to be about 96 feet wide. I tested the rest of the drawings and found them all to have scale inaccuracies. Site drawings were the worst, as the percentage of error was magnified because of the larger scale. (I think it was 1 inch = 60 feet.)

These scale inaccuracies were the reason I learned about calibrating custom scales on my measuring devices. The Scale Master and the Scalex have this simple-­to-use feature. Step one, find a written dimension, usually on the architectural drawings for commercial work, and most often on a civil or mechanical drawing for industrial work. My favorite dimension to use is the distance between grid lines. 

Step two, input the distance you have chosen into the measuring tool. Step three, measure the written dimension on the plan sheet. That’s how you define a custom scale. 

The number of custom scales the measuring device can memorize depends on the device model. If you are using an on-screen takeoff product, the software will have its own version of calibrating a custom scale.

Since I first became aware of inaccurate scales, the problem has only become worse. It is now a standard practice in my company to verify the scales on every page of every project. This is a little time­ consuming, but it can save you from a scenario such as measuring a 1,000A feeder at 100 feet when it should be 200 feet. Winning a project because all of your measurements are off by 50% is not an easy thing to explain to your boss.

I often receive plans smaller than their original physical size. An example would be when plans that should be 24 inches tall by 36 inches wide are delivered as 11 inches tall by 17 inches wide. My experience is that reduced-size plans will have inaccurate scales over 95% of the time, often being around 50%.

Next month’s article will continue with more things I was not taught in school.

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