Interface Types
Interface type |
Subjected to overvoltages (i.e. leaves the building) |
Not subjected to overvoltage (i.e. does not leave the building) |
Defined in the standard as |
Requirements |
E1, T1 |
X |
|
TNV1 |
Requirements |
E1, T1 |
|
X |
SELV |
No requirements |
Analog Telephone line, modem (POTS) |
X |
|
TNV3 |
Requirements |
Analog Telephone line, modem (POTS) |
|
X |
TNV2 |
Requirements |
ISDN S |
|
X |
SELV |
No requirements |
ISDN U |
X |
|
TNV1 |
Requirements |
Ethernet10base-T 100Base-T |
|
X |
SELV |
No requirements |
xDSL lines - Line Voltage above 120V dc |
|
X |
RFT |
Not covered by IEC60950 |
xDSL lines - Line Voltage up to 120V dc |
X |
|
TNV3 |
Requirements |
E1,T1 (TNV1) All PRI interfaces, which connect to the Central Office, should comply with the TNV1 insulation requirements.
DESIGN REQUIREMENTS |
DESIGN GUIDE |
Accessibility |
No access to E1,T1 connectors with the TEST PROBE No access to E1,T1
circuits with TEST FINGER |
Voltage limitations |
Do not exceed SELV requirements (42.4Vp, 60Vdc) |
Physical spacing |
No requirements |
Electrical separation |
E1,T1 circuits Shall be separated from SELV circuits by 1000Vac or 1414Vdc (sample diagram 1) (See Note) E1,T1 circuits Shall be separated from Mains circuits by
2000Vac or 2828Vdc for US (sample diagram 2) (See Note) E1,T1 circuits Shall be separated from
Mains circuits by 3000Vac or 4242Vdc for Europe (sample diagram 2) (See Note) |
UL over-voltage |
Need to perform tests for overvoltage from line crossing |
Protection of Telecommunication wiring from Over-heating |
If E1, T1 provides remote power feeding (DC phantom voltages) the following apply:
- Connecting wires and cables AWG is clearly defined in installation instructions.
- OR, the current is limited to 1.3A
During compliance testing output is going to be overloaded (all the way down to a short) to see if requirements are met. (See Note) Recommendation- limit current to telecom network to 1.3A. |
Separation from earth |
It is very important to separate the telecom network from the earth bonding in your product. Recommendation- Any over-voltage protectors (Gas Arrestors or similar) which are connected to the earth bonding of the product shall have a minimum DC sparkover voltage of 1.6 times the
rated voltage of the unit. There are exclusions for separation from earth if voltage protectors have DC sparkover voltage of less than 1.6 time of the voltage rating of the unit. |
Note: Standard allows additional testing options- Contact your testing lab or Ask the Expert
POTS lines, xDSL lines, ISDN U interface (TNV-3)
POTS (Plain Old Telephone System) refers to typical telephony lines for which there is always a DC remote power feeding voltage, audio signal is superimposed on the DC signal, ringing signals exist on the
line for short periods of time.xDSL lines are high frequency links that can reach very high data rate speeds for long distances. Typically a DC component is used for
remote power feed. This voltage may be a few hundred volts. ISDN U interface is typically connected to the central office unlike ISDN S interface which is typically considered a SELV interface.
DESIGN REQUIREMENTS |
DESIGN GUIDE |
Accessibility |
No access to TNV3 connectors with the TEST PROBE No access to TNV3
circuits with TEST FINGER |
Voltage limitations |
Europe- 120Vdc and 70.7Vp. For voltages other than ringing voltagesUS- 60Vdc and 42.4Vp. For voltages
other than ringing voltages Recommendations-
- Ringing voltage must comply with one of the following
- Europe and US: Current through 5Kohm shall be less than 20ma for continuos ringing
- US only: 200Vp or 300Vpp voltage max over a 1Mohm
- Other rules also apply for cadence ringing . Consult your safety lab for details or refer to annex M.2 and M.3 in IEC60950
|
Physical spacing |
Basic insulation required.Recommendations
-As a rule of thumb, design with insulation gap between telecom circuitry and SELV circuitry of 1.5mm |
Electrical separation |
TNV3 circuits Shall be separated from SELV circuits by 1000Vac or 1414Vdc (sample diagram 1) (See Note) TNV3 circuits Shall be separated from Mains circuits by
2000Vac or 2828Vdc for US (sample diagram 2) (See Note) TNV3 circuits Shall be separated from
Mains circuits by 3000Vac or 4242Vdc for Europe (sample diagram 2) (See Note) |
UL over-voltage |
Need to perform tests for overvoltage from line crossing |
Protection of Telecommunication wiring from Over-heating |
The following apply:
- Connecting wires and cables AWG is clearly defined in installation instructions.
- OR, the current is limited to 1.3A
During compliance testing output is going to be overloaded (all the way down to a short) to see if requirements are met. (See Note) Recommendations- limit current to telecom network to 1.3A. |
Separation from earth |
It is very important to separate the telecom network from the earth bonding in your product. Recommendations-
- Any over-voltage protectors (Gas Arrestors or similar) which are connected to the earth bonding of the product shall have a minimum DC sparkover voltage of 1.6 times the rated voltage of the unit.
There are
exclusions for separation from earth
if voltage protectors have DC sparkover voltage of less than 1.6 time of the voltage rating of the unit. Consult your safety lab for details.
Some modern SLICs offer no separation from earth. They are typically supplied by DC directly to the SLIC. These SLICs comply with safety requirements only if DC voltage, supplied to the SLIC, which
becomes ringing voltage on the tip and ring is kept at SELV levels of 60Vdc or below.
|
Note: Standard allows additional testing options- Contact your testing lab or Ask the Expert
PBX telephone lines (TNV2) PBX telephone lines are intrabuilding lines which are not exposed to
overvoltages.
DESIGN REQUIREMENTS |
DESIGN GUIDE |
Accessibility |
No access to TNV2 interface connectors with the TEST PROBE
No access to TNV2 interface circuits with TEST FINGER |
Voltage limitations |
Europe- 120Vdc and 70.7Vp. For voltages other than ringing voltagesUS- 60Vdc and 42.4Vp. For voltages
other than ringing voltages |
Physical spacing |
Basic insulation required.Recommendations
-As a rule of thumb, design with insulation gap between telecom circuitry and SELV circuitry of 1.5mm |
Electrical separation |
TNV2 interface circuits Shall be separated from SELV circuits by 897Vac or 1268Vdc (sample diagram 1) (See Note) TNV2 interface circuits Shall be separated from Mains circuits
by 2000Vac or 2828Vdc for US (sample diagram 2)
(See Note) TNV2 interface circuits Shall
be separated from Mains circuits by 3000Vac or 4242Vdc for Europe (sample diagram 2) (See Note) |
UL over-voltage |
Not Applicable |
Protection of Telecommunication wiring from Over-heating |
The following apply:
- Connecting wires and cables AWG is clearly defined in installation instructions.
- OR, the current is limited to 1.3A
During compliance testing output is going to be overloaded (all the way down to a short) to see if requirements are met. (See Note) Recommendations- limit current to telecom network to 1.3A. |
Separation from earth |
It is very important to separate the telecom network from the earth bonding in your product. Recommendations-
- Any over-voltage protectors (Gas Arrestors or similar) which are connected to the earth bonding of the product shall have a minimum DC sparkover voltage of 1.6 times the rated voltage of the unit.
There are
exclusions for separation from earth
if voltage protectors have DC sparkover voltage of less than 1.6 time of the voltage rating of the unit. Consult your safety lab for details.
|
Sample Testing DiagramsNo 1 
No 2 
OVER-VOLTAGE PROTECTION FROM LINE CROSSING NOTE-
Over-voltage testing is conditioned by many variables. The following is the basic set of requirements only. It is highly recommended to consult your test lab at the beginning of your design.
In the US testing for overvoltage from line crossing is defined in UL 1950. It is mandatory to do this test for the US. In Europe, the standards that apply to overvoltages from line crossing
are ITU-T K20, K21. The application of these standards is not mandatory and depends on the specific requirements of the end user. During over-voltage testing up to 24,000VA are placed on the tip and
ring of the telecom interface. The results can be destructive. During over voltage testing the following voltages are typically applied in common and metallic modes.
- 600Vrms 40A for 1.5 seconds (with 2A fuse)
- 600Vrms 7A for 5 seconds (no fuse used)
- 600Vrms 2.2A for 30 minutes (no fuse used)
Many vendors offer protection solutions. See following for components and Application examples Teccor: http://www.teccor.comRaychem: http://www.raychem.comWickmann: http://www.wickmann.com Littelfuse: http://www.littelfuse.com
Exclusions for separation from earth for telecom interfaces The requirements of separation from earth do not apply to any of the following:
- PERMANENTLY CONNECTED EQUIPMENT
or PLUGGABLE EQUIPMENT TYPE B;
- equipment that is intended to be installed by
SERVICE PERSONNEL
and has installation instructions that require the equipment to be connected to a socket-outlet with a protective earthing connection
- equipment that has provision for a permanently connected
PROTECTIVE EARTHING CONDUCTOR and is provided with instructions for the installation of that conductor.
NOTE – In Finland and Norway, the exclusions are applicable for PERMANENTLY CONNECTED EQUIPMENT and PLUGGABLE EQUIPMENT TYPE B only. |
