Installation guide

Network Infrastructure for EtherNet/IP™
7-83
Selecting Components
7.2 Cabling Considerations: Twisted-Pair vs. Fiber-Optic Cable
Deciding whether to use fiber-optic cable or twisted-pair copper cable depends on specific application and
environmental requirements. Users need to compare capabilities to find the right match for their
requirements.
• Fiber-optic cable is inherently impervious to noise from electrical and magnetic fields.
• Fiber-optic cable may cost more per foot than standard, twisted-pair cable; however,
users should consider the cost of installation for either type of cable.
• Fiber-optic cable has fairly stringent requirements regarding bend radiuses. (See 7.2.5
Bend Radius / Pull Force of Fiber.)
• Shielded twisted-pair cable has been found to be resistant to some types of electrical
noise; however, ground loops must be avoided. (See 7.2.1 When to Use Shielded Twisted-
Pair Cabling.)
• Fiber-optic cable can provide immunity to lightning and is a good choice between
buildings or in other outdoor areas.
• Fiber-optic cable is a good option within hazardous areas. If it is necessary to mix
communications cabling with high-voltage runs, fiber optics is superior to twisted-pair
cabling due to the limited breakdown voltage rating of twisted-pair cable and potential
noise coupling.
• Although not completely immune to security breaches, fiber-optic cable is much more
difficult to tap into and access unauthorized data.
• Twisted-pair runs are limited to 100 meters (328 ft); fiber-optic cable can provide much
longer transmission distances. Typical multi-mode installations allow distances up to 2
kilometers (1.24 mi), but single-mode installations can be 30 kilometers (18.64 mi) or
greater.
• With both fiber-optic and copper cables, the cable jacket specifications for weld splatter,
moisture, and UV (sunlight) resistance must be considered.
7.2.1 When to Use Shielded Twisted-Pair Cabling
Engineers need to select the correct cable for the environment. Cable selection is dependent on the
planned cable route. Shielded cable may perform better than unshielded cable in high-noise industrial
environments. In particular, if an application is in a high-noise environment or a cable must be run in
close proximity to noise-radiating sources, shielded or fiber-optic cables should be used.
Shielded cables are appropriate if an application includes one or more of the following:
• Motor-control centers
• Induction-welding processes
• Proximity to high-power RF radiation