T 4.4 Impairment of lines due to environmental factors

The transmission characteristics of cables transmitting electric signals can be adversely affected by electric and magnetic fields. Whether this will actually lead to a disruption in the transmission of the signal depends mainly on the following factors:

• frequency range, intensity, and duration of exposure to the fields,
• cable shielding, and
• safeguards during data transmission (redundancy, error correction)

Many causes of impairment can be identified in advance:

• Strong magnetic fields are generated along high-voltage lines and in the vicinity of large engines (railroad, production plant, elevator).
• Electromagnetic fields (radio, police/fire department, service radio, paging systems, wireless networks) can be generated in the vicinity of transmitter installations.
• In some cases, the transmitting power of mobile telephones exceeds the electromagnetic susceptibility limits of IT systems.
• Cables can influence each other through mutual induction.

Environmental factors other than just electrical or magnetic fields can also have an effect on a cable:

• high temperatures (in industrial production areas, for example),
• aggressive gases, and
• high mechanical stresses (e.g. on lines to portable devices or when temporarily laying cables on floors)