In a previous column, I discussed the transfer of symbol counts to the material listing sheets. Labor units are derived from the materials to be installed, so the complete listing of all nomenclature is critical.

Using assembly units makes listing painless. Computer estimating software options are usually based on assembly units. Obviously, using assembly units prepared by a software firm can be of great assistance. But for those just beginning their estimating careers, the process of "exploding" a plan symbol is still the best foundation for understanding abilities of computer programs. Manually dissecting an assembly unit will be instructive for altering the standards listed in computer-prepared assembly units.

Estimators also need to know the quantities of an associated item. Common symbols used in the electrical industry are "E" for each, "C" for 100 of an item, and "M" for 1,000, (usually used for wire).

While most descriptors in The NECA Manual of Labor Units are consistent with pricing services' listings, some do vary. For example, the manual lists Rigid Steel Elbows labor for each, or as "E,"while the pricing reporting services list the price for that elbow per hundred, or as "C." Since the same quantity multiplier is used for both labor hours and material costs, it becomes important that the designator for material match that of the labor. This matching of descriptors will ensure that when the manual extension is done, the extension will be accurate and speedy.

This detailed listing of individual items or assemblies will be the base used for the application of appropriate labor units. Addition of decimals instead of minutes avoids the possibility of errors. The NECA Manual of Labor Units includes a typical conversion chart based on minutes.

A simple formula, such as dividing the number of minutes by the 60, will also produce the desired decimal. In addition to accuracy converting time to decimals, it can speed the extension process when both time and dollars are in decimal form.

Applying the proper labor unit that will produce the winning bid- and a profit for the contractor - ranks among an estimator's greatest challenges. Beginning estimators yearn for a prescriptive set of labor units that will solve all the ambiguities.

Unfortunately, labor units such as those used in the auto repair units are neither available nor applicable for electrical work.

Considering the many conditions encountered in construction projects, labor units for various installations are at best advisory.

Published labor units have many built-in variances. These differences must be understood before such units can be used. Through experience and adjusting data, estimators have established or refined reliable labor units. Proprietary labor units are a contractors trade secret and should never be disclosed or abused.

There are many published labor tables, but many do not provide a basis for the data. NECA's labor units were first published in1923, and they continue to be revised regularly. They are dependable standards. Still, estimators must realize that they are responsible for using any labor units correctly. This task cannot be taken lightly, nor should it be delegated to inexperienced estimators.

There are great discrepancies between labor tables. Each section of The NECA Manual of Labor Units includes a scope of included work and a listing of those items that a contractor should consider before completing the bid. Without a like comparison of all available labor tables, using such tables becomes a gamble.

One of the factors affecting labor units is the amount of repetitive work. It's obvious that the installation of one fixture will take much longer than would ten. Some customers will not understand this situation. To analyze the time required for a particular material item requires a task analysis listing all steps needed. A lighting fixture does not magically appear at the installation site; many operations precede the actual installation. If the quantity increases then many of the preceding operations will be done for ten fixtures instead of one, except the actual installation of the fixture. The NECA Manual of Labor Units, as an example, uses a base of a building that is 20,000 to 100,000 square feet in size, with fixture quantities and devices that match buildings of such size.

Particularly on change orders, awarding authorities tend to suggest - or require - the use of some specific labor tables, and prohibit the use of others. Estimators knowledgeable on the subject of labor tables should professionally resist requests or orders of such a nature.

For example, a project was located where the federal government required that a specific publisher's labor units be used. The irony of the order was that the publisher in his foreword warned the user that the labor tables should not be used in that state, more than likely due to the geographic locations. Bring such a situation to your clients' attention.

Today, most estimating is done with computers. Many contractors turned to early versions of estimating software, only to find out that their labor units were fictional. That's no longer the case, to say the least.

So, before blindly using estimating programs, scrutinize the labor units, the depth of the assembly units, and the ability to customize the labor units. All must be considered. It is no different with manual estimating practices, where the estimators can custom-fit the labor units to specific expectations of the project.

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 edavid@lbcc.cc.ca.us.