Editor's Note: Thanks to Peter Cox, cable expert, and a Project Manager in Belden’s Industrial IT group, for his contribution to this article.

From subsea drilling 6,000 feet below the surface to pipelines that cross many landscapes to intense refining processes, the range of conditions for oil and gas installations is very broad. As a design engineer, you may be involved with many types of projects with very different requirements. How then do you approach selecting the right cable for an oil and gas application?

But won’t any cable do? Certainly not! Cable issues account for more than 70% of signal transmission issues and they are difficult to diagnose and resolve. With downtime costing thousands of dollars per hour, availability requirements demand that the right cable is specified for each use.

The good news is that despite the broad range of oil and gas applications many of them share common cable requirements. In this article I take away the voodoo and spell out the 3 easy steps to selecting the right cable.

1. Select the Right Industrial Cable Jacket

As a resident of the Pacific Northwest I know that snowboarding is fun when I have the right layers on and walking my dog in a downpour is okay when I am in water repellant outerwear from head to toe. Having the right outerwear, or jacket, is also the key to signal reliability for oil and gas applications.

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Thus the first question to ask yourself is “How harsh is the environment for my project?” The answer to this leads to selecting the right industrial cable jacket.

The table below categorizes various types of oil and gas applications according to a harsh, harsher, harshest model and indicates the type of cable jacket suitable for each.

Fig2_TypesofCableJackets

Figure 2 - Suitable cable jackets for harsh, harsher and harshest oil and gas applications. (Click here for larger image)

2. Select the Level of Oil Resistant Cable Needed

Now that you have narrowed down the range of suitable jacket types, what level of oil proof cable do you need? Will the cable be exposed to:

  • Infrequent light splashing? If so choose an “oil resistant” jacket.
  • Periodic oil exposure? Then choose a jacket that is “UL Oil Resistant 1”.
  • Frequent harsh oil exposure? This situation requires “UL Oil Resistant 2”.

Use the following chart to narrow down and select the jacket type for your project.

Fig3_CableJacketsforVariousEnvCond

Figure 3 – Cable jacket types suitable for various environmental conditions. (Click here for larger image)

For those of you who like to know what all of the acronyms that describe cable are, here is a summary.

Fig4_CableAcronymsDecoded

Figure 4 – Cable acronyms explained. (Click here for larger image)

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3. Special Considerations by Industrial Cable Type

The three most common cable types used in oil and gas applications are Ethernet, VFD and Control and Instrumentation cable. Let’s take a look at the unique selection criteria for each.

a. Ethernet Cable

Should it be Copper or Fiber?

The key considerations for choosing copper or fiber Ethernet cable are:

  • If you have runs of 100 meters you need fiber
  • If you need data rates of more than 1GB than you need fiber
  • If you need Power over Ethernet then you need copper

Twisted or Bonded-Pair Conductors?

Bonded-pair cables provide resistance to the rigors of installation by utilizing a manufacturing technique that affixes the insulation of the cable pairs along their longitudinal axes so no gaps can develop between the conductor pairs.

Twisted pair cable construction can be susceptible to pair-gapping during installation, as well as impedance mismatches.

Belden has developed proprietary bonded-pair technology that provides:

  • Uniform conductor-to-conductor spacing, or centricity due to the absence of gaps between the conductor pairs.
  • Superior electrical performance thanks to the uniform centricity. Installation processes, such as bending, pulling and twisting, do not affect the high functioning of this cable.
     
Fig5_BondedPAirAdvantage

Figure 5: Twisted pair conductors have gaps which decrease performance. Belden’s patented bonded-pair technology maintains electrical performance even when cable is bent, pulled or twisted. (Click here for larger image)

b. VFD Cable

Many motor systems are used to pump or refine oil and gas. Often these motor systems use Variable Frequency Drives, or VFDs, to precisely control their speed, as doing so greatly reduces both costs and energy consumption. In addition, VFDs also improve process control, reduce manufacturing waste, provide a longer useful life for motors, reduce maintenance and deliver high reliably.

However, there is a downside to VFDs, and that is that they generate disruptive electrical noise in the environment around them that can create problems in the refining or pumping processes. The noise emission can be difficult to track down and eliminate, causing reduced production or downtime.

Proper cable shielding is thus essential for VFD cable, particularly when longer cable runs are required. Choosing well-designed, robust VFD cables ensures motor uptime and reliability of the VFD system and also provides protection for any sensitive instrumentation and adjacent control systems.

A challenge in purchasing VFD cables is that there are no standards for them. Thus it can be difficult to differentiate between minimum construction-grade cable sold as VFD cable and high-performing VFD cable that protects motors and ensures the maximum benefits of a VFD system.

Below is a quick guide to help you differentiate between the two.

Fig6_VFD-Cable-Character

Figure 6: Key cable characteristics for High Performance VFD Cable.
(Click here for larger image)

c. Instrumentation and Control Cable

In addition to selecting the right jacket type, as shown in Figures 2 and 3, the important thing to determine for Instrumentation and Control cables is the type of insulation.

Here are the guidelines:

  • For Harsh environments choose PVC or PVC nylon insulation
  • For Harsher environments, choose PVC nylon, or XLPE insulation
  • For Harshest environments, choose XLPE insulation


The Right Industrial Cables Deliver High Performance and High Availability


Just like I don’t go to the mountains to snowboard without the right clothing layers and protective gear, so you don’t want cable without the right layers and protection.

If you follow the steps in this article:

  • Select the right industrial cable jacket
  • Select the level of oil resistant cable needed
  • Remember the special considerations by industrial cable type:
    • Ethernet – copper or fiber, bonded-pair technology
    • VFD – choose high performance cable characteristics
    • Instrumentation and Control – select the right insulation

you will choose a cable that provides reliable signal transmissions and high availability.

Here are some examples of the 3 types of cables for each level of environmental harshness:

Fig7_CableExampes

Figure 7: Possible high level cable specification for different environmental conditions. 
(Click here for larger image)

Good luck with your projects and I look forward to hearing whether these guidelines help.

Related Links

Ethernet Cable:


VFD Cable:


Instrumentation & Control Cable:


Marine Certified Cable