Secrets to Estimating Datacom Work, Part 2

Aug 1, 2000 12:00 PM, By Paul Rosenberg

Knowing the steps involved with installing optical fiber systems can keep you from losing your shirt on your next datacom estimate.

Last month, we explained a number of differences between conventional electrical estimating and datacom estimating. This month, we'll go over some particulars regarding estimating optical fiber work.

The only real problems associated with estimating fiber jobs is that this is a fairly new technology for electrical types. Therefore, many people are not yet completely familiar with it. The risk is you will leave things out when preparing your estimate. Let's look at some of the pitfalls to avoid.

Fragility delays. Since optical fibers are vulnerable to damage, you must handle them differently than copper cables. This will require you to use higher labor units for these cables than you might use for similar sized copper cables. The estimating process for optical fibers is similar to other cable estimating processes, but the labor units you use will need to be a bit higher (10% to 20%), to account for the extra care.

The cables are usually tougher than copper cables. It's the glass fibers that are fragile. Because of fragility, you can't pull the cables with too much tension. Testing. Optical fibers and cables require more testing than copper conductors and cables. The first testing procedure is inspecting the cable upon delivery. In addition to this, you must include extra testing time for each fiber installed. Remember: This is testing for each fiber, not each cable.

All the parts. To avoid leaving things out of your estimates, you should think through the design of the installation carefully before you arrive at your final selling price. It might also be a good idea to put a bit of contingency money in your estimates. A small percentage of your total cost should be all you need.

The parts of a typical optical fiber installation include: cables, terminations (connectors), splices, breakout kits, grounding clamps, cable lubricant, pulling hardware, cross-connects, patch panels, cable boxes, splice boxes, racks, conduits, inner duct, tie-wraps, jumpers, cable markers, attenuators, distribution cabinets, outlets, and jacks.

Connector yields. Although fiber connectors are becoming more foolproof, a certain number of connectors will fail simply due to the difficulties associated with sanding and polishing hair-thin glass. Trained technicians can expect losses of 6% to 8% in the field.

Loose tubes and gel. When you estimate loose tube cables, add some extra time for cleaning up the gel that oozes from them. You must also account for paper towels and alcohol (or some other cleaning agent).

Necessary supplies. There are certain items you must have to get the fibers in place, terminate them, and test them. You should account for these items in your estimates: swivel pulling eyes, breakaway swivel or tension meter, microscopes, polishing fixtures (usually called pucks), termination kits, sandpaper, adhesive syringes, cleavers, stripping tools, solvent and wipes, canned air, and adhesives.

The communications closet. In buildings, the wiring closet is almost always unfit. (Designers created these rooms to minimum sizes 20 years ago, when they expected only a few telephone cables).

While itemized estimating is the most commonly used and safest method of estimating, it's not always the best method. Unit pricing has distinct advantages. Giving customers a price "per each" often works better for them.

A great deal of subcontract fiber work entails primarily the installation of connectors, or as it is commonly called, making terminations.

Although estimating datacom work has aspects that are different from estimating power wiring, the process is similar. As supply channels improve and the industry becomes more familiar with it, the process will inevitably become easier. But for now, you'll have to pay close attention.

Sidebar: The Take Off

The process of "taking off" datacom systems is essentially the same as the process used for conventional electrical estimating. By taking off, we mean the process of taking information off of a set of plans and/or specifications, and transferring it to estimate sheets. For datacom work, this requires the interpretation of a completely new set of graphic symbols.

Rules that apply to the datacom take off include:

Review the symbol list. Datacom systems are by no means standardized. Make sure you know what the symbols represent.

Review the specifications. Obviously, it's necessary to read a project's specifications, but it's also important to review the specifications before you begin your take off. Doing this may alert you to small details on the plans you might otherwise overlook.

Mark all items that have been counted. Again, this is common sense, but a lot of people do this poorly. Your objective should be to clearly and distinctly mark every item as you count it.

Always take off the most expensive items first. By doing this, you assure you will have numerous chances to catch something you may have missed in a first or second pass through the plans. This way, if you do make a mistake on a last pass over the plans, it will be with a less expensive and less critical component.

Obtain quantities from other quantities whenever possible. For example, when you take off conduit, don't try to count every strap needed. Instead, simply calculate how many feet of pipe will be required and then include one strap for every 7 ft to 10 ft of pipe.

Do not forget vertical runs. As you take off cable or conduit runs, remember they will have to go up or down to serve their loads. Do not forget to count the rises and/or drops.

Do not rush. Cost estimating is a slow, difficult process. To do a good estimate, you must perform a careful, efficient take off.

Develop a mental picture of the project. As you take off a project, picture yourself in the rooms, looking at the items you are taking off. Picture the item in its place. Make note of its surroundings and how it connects to other items in the room.