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Shoestring Fieldbus a Bad Idea

June 22, 2009
Rezabek's Risky Proposition in His Article, “Fieldbus on a Shoestring,” Causes Controversy. Read Our Readers' Responses
This article was printed in CONTROL's June 2009 edition.

In the recent article, “Fieldbus on a Shoestring,” (Jan. ’09, p. 31), John Rezabek suggested a risky proposition—cutting corners during the economic recession by using nonstandard cable for fieldbus applications. He cited tests he’d seen in which non-fieldbus cable performed in a fieldbus lab situation. 

Then Rezabek takes a leap by assuming that a cable that performs in a cozy lab setting will perform similarly in the field, where electrical noise, temperature extremes, chemical, moisture and UV exposure are inevitable and unpredictable. 

Rezabek purports it’s worth taking the gamble that the cable will perform. He suggests that you can replace it later when the economy improves, or address deficiencies, if and when they arise, as long as “your projects and business demands will tolerate a little back-pedaling.” 

In today’s precarious economy and job market, is that a gamble you are willing to take? Can you afford to take responsibility for a plant’s significant downtime, while the source of the problem is investigated?

Rezabek proposes designing risk into your projects. Many engineering, manufacturing and industrial cable experts would agree that’s not a smart gamble. 

An improperly designed, implemented and installed physical layer is the Achilles’ heel during start-up and commissioning.  One problematic segment can throw the whole network into a tailspin. It is more cost-effective to use the proper tools from the outset. Also, consider how relatively inexpensive material is compared to the cost of labor.

ISA-SP-50 specification defined Type A cable with precise requirements, while Type B and Type C cables had progressively looser specifications. Type B and C cables and the resulting difficulties in real-world conditions prompted the Fieldbus Foundation to replace the problematic ISA specification with the new FF-844 specifciation, which eliminated unsuitable Type B and C cables to ensure reliability and uptime.

Choosing cable other than that specifically designed for fieldbus applications is like using diluted antifreeze in a new truck in Wisconsin. It will be OK in the fall, but it won’t be pretty in December when temperatures drop well below zero. 

It’s a costly risk for very little savings. You probably wouldn’t be willing to depend on a non-standard product for your new vehicle. So, why would you consider it for industrial networking projects?  Designing the physical layer on the cheap is not economical.

British author and social commentator John Ruskin (1810—1900) wrote: “It’s unwise to pay too much, but it’s worse to pay too little. When you pay too much, you lose a little—that is all. When you pay too little, you sometimes lose everything because the thing you bought was incapable of doing the job it was bought to do. The common law of business balance prohibits paying too little and getting a lot. It can’t be done. If you deal with the lowest bidder, it is well to add something for the risk you run, and if you do that, you will have enough to pay for something better.” 

Rezabek said, “In times of hardship, I’ve been known to compromise.” Part of the challenge of the recession is not simply to cut costs now, but to work smarter, to reengineer, and redesign the way you work so you’re more efficient for the long term.  Looking only at the short term is shortsighted. Rolling the dice with what you have as Rezabek suggests is taking unnecessary chances with your company’s productivity and potentially your job.

Northwire and other reputable, service-oriented cable manufacturers strongly advocate meeting customers’ requirements and the Lean principle of perfect first-time quality. The insignificant cost difference between standard cable and fieldbus is not worth the risk.

No one knows when the present economic recession will end. Therefore, we all need to step up efforts to reduce waste, but not at the risk of creating potential crises.

Sandy Fulton
Product manager
Northwire, Inc.
Osceola, Wis.

Rezabek Responds

It was not my intent to throw quality cable suppliers like Northwire “under the bus” as it were.

As Northwire’s Sandy Fulton and Jim Berkey can attest, the three of us have sat through Mike Miller’s (Duke Energy, retired) presentation where he describes how three 800+ megawatt nuclear power plants in South Carolina were outfitted with numerous fieldbus devices, all using existing decades-old cables at least three times—far from a “nice cozy lab” situation.

I use Northwire’s products and have mentioned as much in my “Parity Check” column (Industrial Networking, 4Q ’08, p. 29) on at least one occasion. It is an excellent product, arguably superior to competing supplier’s offerings. Northwire has a repertoire of creative solutions that can even save me some money, such as a non-armored cable that has the crush strength of armored. But fieldbus’s physical layer was designed to allow use of existing cable, hence the definition of Type “B” and Type “C” installations. The architects of fieldbus anticipated as much.

End users are a bit dismayed when quality suppliers use alarmist statements to make their products appear indispensible. I have seen videos from a leading valve supplier of refineries in flames after daring to use third-party valve trim. An SIS supplier recently ran a campaign of info-webcasts where similar flames were shooting out when people integrated their SIS with their DCS. These campaigns were all by premier suppliers (both of them the preferred vendor at our site) on par with Northwire in their respective specialties.

As an engineer, I am constantly making judgments about “how much insurance do I want to buy.” We are paid to make a prudent choice, not to practice risk aversion at all cost. My column was about choices that were worth exploring in a tough economic climate. Duke Energy chose to use existing wire for reasons other than saving money, but they did and it has worked flawlessly. I would encourage users to use the best hardware they can afford, but fieldbus is about “freedom to choose,”  and wire—existing  or new—is one of those choices.

Critical Assets or Asset Foolishness?

[Over on Joe Weiss’ Unfettered blog (www.controlglobal.com/unfettered), in an exchange about how many “critical assets” electrical firms really have, “ab3a” made the following comments.]

 “This is the problem with orienting a policy for infrastructure protection around assets instead of functionality. 
“In an N+1 condition, are any one of the generating plants critical? No.  Others will take up the slack. But if you take out any two of the generating plants, do you have a problem? Of course!

“So which generating plants are critical? The question is insufficient to answer the need for reliable, safe power. We simply need to ask better questions and define the mission more carefully. This goes as much for the load as it does the generation side of things.”

[To read the entire exchange and see a map prepared by NPR of the concentration of power plants across the country, go to http://community.controlglobal.com/content/we-dont-got-show-you-no-steenkin-critical-assets.] 

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