This is newsletter #27 in the series. If you have missed prior newsletters, and are enjoying the series, we encourage you to purchase the complete Electrical Estimating Program. Click on the coupon at the bottom of this page.

An estimate is only as accurate as the take-off information used to produce it. One key component of a quality takeoff is measuring accurately. Measuring consists of determining the circuit length for branch circuits, feeders, and service raceways or cables. Before you begin, verify the architectural scale listed in the drawings. Test the scale to ensure its accuracy against something that you know the size of. Drawings are sometimes duplicated by a copy center and reduced in size. If you’re using electronic drawings, don’t rely on the printed scale or the settings of the file. Verify a few items before you start to ensure accuracy. A little variance in the scale can result in a huge change in your measurements.

Scale dimensions should be noted in the drawing title block; however, the scale might be different on different pages, or different sections on the same page. If you are not careful, measurements can be off by as much as 100 percent. For example, you might think you are working a ¼ in. per foot scale drawing, and it is actually a half size drawing that is at 1⁄8 in. per foot scale.

Tools used to measure the circuits (on a printed drawing) include an architectural ruler, a scaled measuring tape, a mechanical measuring device, or an electronic measuring wheel. The architectural rule is fine for a few quick measurements and verifying the drawing scale, and estimators may use a measuring tape for 1⁄8 in. and 1/4 in. scale drawings in the field. However, the electronic scale wheel is the most convenient when completing an entire bid since it can easily be set to multiple scales and includes a built-in counter to assist in the takeoff.

Once you have counted symbols (fixtures, switches, and convenience receptacles), measure the branch-circuit wiring that supplies those openings. When measuring each run, be sure to add in the drops for the overhead circuits for the switches, receptacles, and terminations at panels. Many estimators place a scaled line on the printed drawing to represent the distance of the drops so that when they come across a drop for an outlet or switch opening, they simply measure the distance from the pre-scaled line.

Author’s Comment: Electronic scale wheel devices permit you to press one key to add a constant distance to the totals. But if your drops are different lengths, the constant will have to be reset. This is where computerized takeoff can save a huge amount of time.

When measuring branch circuits, take-off the 2-wire circuits first, the 3-wire circuits next, then the 4-wire circuits. When measuring the circuit wiring, trace the line that represents the path you plan to take with the wiring using a colored pen or pencil. It doesn’t matter what color you use, just be consistent (see the graphic below).

Author’s Comment: If the drawings don’t indicate the circuit layout (most don’t), you must perform this task first and then measure the circuit wiring.