Cabling Requirements for Harsh, Industrial Applications
By Peter McNeil
This white paper will explain the difference between traditional commercial controlled environments and harsh, industrial environments as well as the type of cabling and interconnectivity products to specify when designing networks for the later. Additionally this white paper includes information on the two popular standards for measuring and rating harsh environments, IP and NEMA.
Introduction Requirements for cabling and other interconnectivity infrastructure products vary widely when comparing traditional commercial environments such as office buildings to industrial environments which include factory floors, processing facilities and waste water treatment plants. Standard commercial environments are generally free from fine particulates, liquids and extremes in temperature. While industrial environments contain some or all of these conditions as well as shock, vibration and EMI /RFI interference. Traditional "controlled" environments Traditional environment can include SOHO, SMB and large Enterprise networks where interconnect components are not exposed to dust, moisture, chemicals, or radio frequency and electromagnetic interference. For these installations there are many products to choose from which are available from a host of manufacturers and suppliers. Much of the infrastructure cabling is placed in the Plenum airspace above ceiling tiles or is run inside of walls where it goes untouched for years. Each IDF and the MDF are typically climate controlled with HVAC systems that keep the premise cabling as well as the active equipment such as switches, routers and servers at a constant temperature and humidity level. In these types of installations a combination of copper UTP and Fiber Optic cabling is generally used. Fiber optic cabling is used for longer runs between floors of a building and also sometimes used underground either in a conduit or direct burial to connect multiple campus buildings. See Figure 1
Industrial "uncontrolled" environments Industrial environments often include manufacturing facilities, both onshore and offshore petroleum processing operations, coal mines, waste water treatment facilities and transportation systems including tunnels, subways etc. These harsh uncontrolled environments include both indoor as well as outdoor installations where temperature extremes, moisture, shock, vibration and exposure to chemicals are prevalent. When designing a cabling infrastructure for these types of conditions special consideration is required. EMI/RFI Often motors and generators are located right next to or in close proximity to network cabling. EMI and RFI can interfere with data transmission on a copper cable and cause downtime and errors. To lessen or eliminate EMI/RFI interference shielded cables and connectors must be used. Typically two types of cable shields are used, braided and foil. Foil shielding provides 100% coverage of the conductors but is hard to effectively terminate to connectors and offers high resistance which does not provide the best path to ground. Braided shield generally offers 60%-85% shielding and can only offer about 95% coverage at best. The mass of the braid is higher than a foil shield and thus provides better conductivity and offers a good secure connection to the connectors at the cable ends providing an excellent ground. Many times shielded cables will utilize both foil and braided shields offering the highest level of protection from EMI/RFI. See Figure 2.
When building a shielded cable plant it is important to use shielded cable, shielded connectors and shielded interconnection points such as patch panels in order for the shielding to be effective against EMI /RFI. Additionally proper bonded grounding of all components is crucial to attaining effective shielding.
Another consideration when designing a cabling plant in harsh environments is the cable jacket. In some cases robotic equipment is directly connected via Category 5/5e or 6 cables that are constantly moving and require a cable that is constructed with a hi-flex , low friction jacket as well as robust connectors to ensure a high MTBF. Other environments call for cabling that can be exposed to petroleum based products or other chemicals. Traditional PVC jacketed cables would break down when exposed to these harsh liquids. If protection of equipment or peoples lives is a design requirement then Low Smoke Zero Halogen (LSZH) jacketed cables should be considered. LSZH cables give off fewer toxic fumes that standard PVC based cable jackets. Typically LSZH cabling is used in confined spaces such as mining operations. Fiber Optics The use of fiber optic cabling in industrial installations has grown over the past years as an alternative to traditional shielded cabling as fiber cabling is impervious to EMI and RFI. Additionally fiber optic cables can extend great distances when compared to copper cables without the use of costly and cumbersome repeaters. Although fiber is more difficult to terminate in the field and costs more that STP cabling the price for fiber has continued to decline over time. With more offshore, lower cost fiber manufacturing this trend should continue. In some cases fiber may only be needed in certain areas of an industrial cable plant near high EMI areas or between facilities where copper falls short due to distance limitations (see figure 3). If this is the case, relatively low cost media converters can preserve the existing copper infrastructure investment and allow access to fiber runs where required.
Harsh Environment Rating Systems
NEMA (National Electrical Manufacturers Association) and the IEC (International Electrotechnical Commission) are two standards groups which have devised rating systems for products such as cable assemblies, enclosures etc., which define the products resistance to dust, moisture, water immersion, and ice. The IEC’s rating is referred to as the IP or Ingress Protection rating. The table below outlines NEMA and IEC IP enclosure ratings. See Figure 4
As far as cable assemblies and IP ratings, proper termination is essential to qualify for an IP rating. The connectors and cable must be properly terminated per the manufacturer specifications in order to effectively meet an IP rating. If the assembly is not built correctly liquids, debris, and fine particulates can eventually cripple a network. Conclusion When designing a network the operating environment must be considered not just for active equipment such as Ethernet Switches but for cabling, connectors, patch panels, wall plates and enclosures as well to ensure optimal network performance.