T 4.4 Impairment of lines due to environmental factors

The channel capacity of cables with electric signal transmission can be adversely affected by electric and magnetic fields. Whether this will lead to actual disruption of signal transmission will basically depend on three factors:

• frequency range, intensity, and duration of exposure;

• cable shielding; and

• safeguards during data transmission (redundancy, error correction).

In many instances, impairment can be identified in advance:

• Along high-tension lines and in the vicinity of large engines, strong inductive fields are generated. (railroad, production plant, elevator)

• In the vicinity of transmitter installations, electro-magnetic fields can exist (broadcasting, police/fire department, service radio, paging systems, wireless networks)

• Portable telephones ("mobiles") exceed the disruption sensitivity of many IT systems due to the strength of their transmission (2 to 4 watts).

• Cables influence each other by mutual induction.

Irrespective of merely electrical or magnetic factors, other environmental conditions may have an effect on a cable:

• high temperatures (during process control);

• aggressive gases, and

• high mechanical stress (e.g. during provisional layout on floors, lines to mobile devices