Our site electrical foreman has us pretty spoiled. We've worked together long enough that I explain many day-to-day jobs without a lot of drafting — sometimes not even a sketch, let alone a bill of materials.
His employer, who has a long-term maintenance agreement with our site, does the procurement for many of the "bulk commodity" items such as conduit, supports, wire and cable. So when we were adding a redundant power supply to a local panel, I said, "Just use some twisted-pair cable for hookup." But when I inspected the completed job later, I was a little troubled to find black and red insulated conductors (not our normal black-and-white standard), solid conductors versus stranded, no shields and silver-gray jackets.
SEE ALSO: Wire and Cable: A No-Brainer?
"The stuff we normally use was back-ordered until Friday," he told me. My nonchalance had some relatively minor consequences — a few more details to mark up on the as-built drawings — but it could have been a bigger issue had this not been wiring contained entirely within a primarily dc local panel.
Many applications subject signal and power cables to weather extremes, moisture, oil and chemicals, temperature extremes, dust, mud, constant movement, vibration, excessive electromagnetic interference (EMI) or "noise," and harmful radiation. An under-specified or incorrectly specified cable might function for a while, but could create issues when one of the elements in our hostile environments takes its toll.
It's our responsibility as engineers and designers to ensure we have the correct material specified to function for the life of the asset. Virtually every engineer has experienced that sinking feeling of "Shucks, that's not what I wanted," when their specification becomes reality. Then he has been compelled to sharpen his pencils for the next go-around. There are many forces at work that can result in substitutions we didn't anticipate.
If you've delegated the procurement of commodities to a third party, one of these forces is the good wire and cable salesperson. Selling a more commoditized and more easily cloned product like cable can be a tough business, and winning a job hinges heavily on price and availability. We might call out a very specific brand and model number in our bill of materials, but such specs invariably contain the infamous phrase "…or equal."
You might as well say, "Just surprise me."
The individual who represents the brand you trust just might take your business for granted, and the other guy, who brings baseball caps and doughnuts, ends up getting the random order. Some contractors even could be savvy (or cynical) enough to gamble that you'll live with the "Brand X" substitution rather than make them rip it out.
Another potential mutation of our requirements can happen in our own trusty procurement department. Its mission in the enterprise is to drive down the cost of the wire, cable and other commodities we're trying to lock down. The same eager army of competing sales professionals calls on the the folks there, and entertains them on the golf course.
While we may celebrate when our projects unfold predictably and operate as intended, the procurement folks are evaluated on how much they reduce costs. When engineering wants to say, "Just get me what I want," procurement has to protest, "Let us do our job."
Our specifications for cable need to be tight enough to allow procurement to enlist a minimum number of potential bidders. It's helpful if engineering and procurement can agree to limit the bidders to a known field of pre-qualified suppliers. With a good understanding of procurement's mission, objectives and priorities, an engineering professional or project engineer can avoid a lot of frustration and optimize his or her effectiveness in delivering projects on time and under budget.
If your job is large enough, you can ask procurement to divide the scope of supply between two or more suppliers. For example, the "winner" gets 70% of the cable on the project, and the next two competitors get 20% and 10% respectively. Samples of each lot of cable can be tested and compared as they are received, and any discrepancies in quality or schedule can be leveraged to scale back one supplier in favor of the next bidder.
While it's easy to take cable procurement for granted, a little effort can help ensure your projects are free of unforeseen surprises, some of which can be nasty and lead to trouble down the road.