Project Puzzlers: How to deal with common estimating mysteries

Four connected puzzle pieces stand upright, surrounded by other scattered puzzle pieces on the table. A man sits on the upright puzzle pieces looking at a book.
Published On
Nov 13, 2020

In many ways, delivering a complete and buildable project is like successfully assembling a jigsaw puzzle. Imagine your puzzle has missing pieces, the pictures aren’t clear or the pieces are the wrong shape. In this scenario, you can’t exchange your puzzle for a complete one. In order to finish it, you will need to create the missing and defective pieces.

Many bid documents I receive resemble the jigsaw puzzle I mentioned above, and the size of the project does not seem to matter. Two pages or 200 pages, most of them have problems. To finish the estimate, I must replace or repair the missing pieces.

Puzzle 1—What is that branch conduit?

Today’s electrical drawings have moved pieces of identifying information—such as feeder schedules, mechanical equipment tables and panel schedules—off the floor plans to other places. In the past, a line on the plans with no hatch marks most often meant two #12 and one #12 ground. This is no longer true. If you make that assumption, you could be leaving a lot of material dollars and labor hours out of your estimate. I suggest you search the tables and schedules for items larger than two #12 or a two-pole, 20A circuit breaker. Next, list this upsized branch on a feeder schedule. When you have finished the listing, takeoff (measure and record) the upsized branch. When you have finished that task, most often the remaining branch is two #12 and one #12 ground.

Puzzle 2—What voltage drop?

Many engineers stopped doing voltage drop calculations for branch conduit a long time ago. Instead, they specify that the electrical contractor needs to upsize the wire after a certain number of feet. You may find this requirement in the specifications or on the plans. For example, “Provide #10 conductors for all 20A circuits longer than 60 feet, and #8 conductors for circuits longer than 175 feet.” The footage requirements vary by project and engineer. Additionally, there may be a statement instructing you to keep the same size wire from the beginning to the end of the circuit. On jobs that do not have a large footprint, this is not much of a problem. On larger projects, it can be a big deal. I am working on a project now that has required most branch circuits to be upsized, many of them to #8 conductors.

Puzzle 3—How long is it?

We are seeing projects now with the drawings marked “Not to scale.” How are we supposed to measure drawings that are not to scale? The answer is, you should never trust a stated scale. For years, I have noticed drawings that are not true to the stated scale. Many are off by more than 20%, always in a way that would make our measurements come up short.

Drawings should be calibrated. This is done by finding a known dimension, most often from the architectural drawings, and applying it to the electrical plan. It is easily done using the custom scale function on electronic plan wheels. Calibrate functions are also available for on-screen takeoff programs.

Puzzle 4—What is that symbol on the plans?

Standard symbol lists usually have a qualifying statement saying, “Not all symbols on this list will be used in this project.” However, what they should say is, “This symbol list does not contain all the symbols shown on the drawings. Good luck figuring out what they are.”

I used to call engineers to clarify unknown symbols. Unfortunately, most engineers do not want to talk to us anymore, or the bid documents require us to go through the specified channels. Therefore, I do some detective work before writing a request for information and then waiting for an answer. For instance, I often see a standard symbol for a special receptacle. Sometimes it is labeled, such as L5-30R. Most of the time there is no label, so I review the panel schedule to determine what circuit breaker is specified for the receptacle. This provides enough information to takeoff something. Even if it is not the exact configuration you may need in the field, you will have something close in your estimate.

The preceding are just a few of the problems with today’s electrical documents. My general philosophy is not to spend a lot time solving a minor problem. Put a reasonable item in your estimate to cover the problem. If it is an expensive item, write a request for information.

About the Author

Stephen Carr

Estimating Columnist

Stephen Carr has been in the electrical construction business since 1971. He started Carr Consulting Services—which provides electrical estimating and educational services—in 1994. Contact him at 805.523.1575 or, and...

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