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Connection of Data and Telecommunications Cables
Data and telecommunication interfaces are classified according to their safety status.
The following table lists the status of several standard interfaces. If the status of a given port differs from
the standard one, a notice will be given in the manual.
Ports Safety Status
V.11, V.28, V.35, V.36, RS-530,
X.21, 10 BaseT, 100 BaseT,
Unbalanced E1, E2, E3, STM, DS-2,
DS-3, S-Interface ISDN, Analog voice
E&M
SELV Safety Extra Low Voltage:
Ports which do not present a safety hazard. Usually
up to 30 VAC or 60 VDC.
xDSL (without feeding voltage),
Balanced E1, T1, Sub E1/T1
TNV-1 Telecommunication Network Voltage-1:
Ports whose normal operating voltage is within the
limits of SELV, on which overvoltages from
telecommunications networks are possible.
FXS (Foreign Exchange Subscriber) TNV-2 Telecommunication Network Voltage-2:
Ports whose normal operating voltage exceeds the
limits of SELV (usually up to 120 VDC or telephone
ringing voltages), on which overvoltages from
telecommunication networks are not possible. These
ports are not permitted to be directly connected to
external telephone and data lines.
FXO (Foreign Exchange Office), xDSL
(with feeding voltage), U-Interface
ISDN
TNV-3 Telecommunication Network Voltage-3:
Ports whose normal operating voltage exceeds the
limits of SELV (usually up to 120 VDC or telephone
ringing voltages), on which overvoltages from
telecommunication networks are possible.
Always connect a given port to a port of the same safety status. If in doubt, seek the assistance of a
qualified safety engineer.
Always make sure that the equipment is grounded before connecting telecommunication cables. Do
not disconnect the ground connection before disconnecting all telecommunications cables.
Some SELV and non-SELV circuits use the same connectors. Use caution when connecting cables.
Extra caution should be exercised during thunderstorms.
When using shielded or coaxial cables, verify that there is a good ground connection at both ends. The
earthing and bonding of the ground connections should comply with the local codes.
The telecommunication wiring in the building may be damaged or present a fire hazard in case of
contact between exposed external wires and the AC power lines. In order to reduce the risk, there are
restrictions on the diameter of wires in the telecom cables, between the equipment and the mating
connectors.