Assuming the estimate is beginning to shape up and there is time to take a “second look” at the projected bid, a variety of methods can be used to verify the numbers.
The second check is used to ensure that the quantities priced, labored, extended, and totaled are accurate.
One way to verify the assumed scale is to measure a known quantity. Fluorescent fixtures, especially those mounted in rows, can be recognized as a standard size. A good-quality scale ruler can be used to measure any deviation from the scale. While the rotometer is the measuring tool of choice, it is an accepted fact that there is an error factor, albeit small, in most operators’ hands. Errors of this type are generally caused by small symbols as well as the estimator’s judgment and are absorbed in the overall takeoff. The scale ruler will provide the stable reference about the quantity of correction factor that is needed. The intent is not to suggest that the scale rule should be used for the takeoff, but only to verify the scale variations, if any.
Next in the order of errors is having used the wrong scale. Obviously, if the estimator used the .125-inches instead of the 1/4-inch-per-foot scale, the company may rue the day they accepted the project. To determine the average liner feet of runs between outlets, the estimate must be done in such a manner that the number of boxes of all types can be readily segregated. An average figure can be determined by dividing the number of boxes into the total square footage. If the wrong scale was used, the figure will be totally out of proportion for the type of work. This is also one of those situations when averages for various project types kept in the company’s database will pay off.
Once the conduit quantity has been verified, verify the wire footage included in the estimate. In a method that was developed by a vendor of an estimating system, the conduit fill was considered based on the old version of the NEC conduit fill tables. Figures derived from this method should only be considered where the buildings are of a normal configuration. By no means should this approach ever be used for any purpose except to check an estimate. The net percentages assuming the use of 2 No. 12 through 5 No. 12 conductors, irrespective of the conduit size, would produce the following:
2 No. 12 conductors @ 67.2 percent;
3 No. 12 conductors @ 16.8 percent;
4 No. 12 conductors @ 1.6 percent; and
5 No. 12 conductors @ 14. 4 percent.
An advantage to making the takeoff in specific divisions is that the number of boxes or flush fixtures can be identified. This information can be a guide to the number of runs between boxes, considering that for every box or flush device a conduit run is required. The number of runs combined with the average length of the runs should approximate the totals of the conduits of the various divisions of takeoff.
An alternative yardstick to verify the number of boxes or flush devices is a check of the number of box connectors included in the estimate. Considering that, with the only legal exception of communication conduits, every power run must have a conduit termination at each end, the total number of connectors divided by two should equal the number of boxes or flush devices.
The branch takeoff will also reveal any discrepancy in the number of three-way switches. Any circuits using three-way switches must have a number of switches divisible by two. Odd counts should be verified. In the overall scope of checking for errors, this is a minor item. The time required to perform a cursory check is insignificant but may indicate other possible errors.
A complete takeoff can also be valuable when estimating the permit fees. At one time, 1 or 2 percent was a safe figure to “throw” at permit costs. In many parts of the country, however, municipalities have latched on to permit fees as the proverbial pot at the end of the rainbow. Some figures used to verify the estimate’s accuracy are also used to set a figure for part of the permit fees.
If the estimate was done manually, check the materials and labor extensions. It is not necessary to check every item; instead, set a dollar figure above which the item will get a second look.
Many checking methods considered can be sidelined with an efficient computer estimating program. Computer estimates also lend themselves to easy comparison with previously bid and completed projects. By using sort codes, specific items can be compared in a variety of spreadsheets, adding to the accuracy of any estimate.
In the final analysis, no one person or system is infallible, and no one person’s work should be accepted on blind faith.
DAVID is a professor of electrical technology at Long Beach City College, Calif., a consultant, and an expert witness. He can be reached at (562) 597-1877or by e-mail at firstname.lastname@example.org.