Remote telecommunications equipment powering

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Remote telecommunications equipment powering

The topic of powering telecommunication equipment by power fed via telecommunications network cable is a hot topic for several people. The catalyst for this is the development of a new IEC hazard based document "IEC 62368-3/Ed1: Audio/video, information and communication technology equipment – Safety – Part 3: Remote power feeding". This document will eventually supersede "IEC/UL 60950-21 Information Technology Equipment – Safety – Part 21: Remote Power Feeding", which in turn was based on "ITU-T K.50 Safe limits of operating voltages and currents for telecommunication systems powered over the network". 

Standards are like politics - if you don't participate you get what you deserve. Bellcore participated in the creation of ITU-T K.50 and that document does reflect North American practice at that time. Bellcore was broken up and the fragmented US telecommunications providers didn't participate in IEC 60950-21 with the result that certain requirements are in conflict with US practice. There was an unsuccessful attempt by some US providers and standards bodies to include US practice - notably GR-1089-CORE - in UL 60950-21, but this was unsuccessful. Hence there is a strong desire to influence the creation of IEC 62368-3. The utilization of spare POTS lines to provide DC power of fibre optic access equipment is a further incentive to internationally standardize US practice.

Terms and their definitions often control the document content and need to be reviewed when harmonizing. Hence this first post lists out relevant terms and their definitions from the published IEC, ITU-T, ETSI and Telcordia documents.

IEC

tnv-0 circuit: tnv circuit whose voltages do not exceed a safe value under normal operating conditions and under fault conditions; and
which is not subject to overvoltages from telecommunication networks
IEC 60065, ed. 8.0 (2014-06)
TNV-1 circuit: TNV circuit whose normal operating voltages do not exceed the limits for an SELV circuit under normal operating conditions; 
and on which overvoltages from telecommunication networks and cable distribution systems are possible
IEC 60950-1, ed. 2.0 (2005-12)
tnv-1 circuit: tnv circuit whose voltages do not exceed the limits for a tnv-0 circuit under normal operating conditions; and
on which overvoltages from telecommunication networks are possible
IEC 60065, ed. 8.0 (2014-06)
TNV-2 circuit: TNV circuit whose normal operating voltages exceed the limits for an SELV circuit under normal operating conditions; and 
which is not subject to overvoltages from telecommunication networks
IEC 60950-1, ed. 2.0 (2005-12)
tnv-2 circuit: tnv circuit whose voltages exceed the limits for a tnv-0 circuit under normal operating conditions; and which is not subject to overvoltages from telecommunication networks
IEC 60065, ed. 8.0 (2014-06)
TNV-3 circuit: TNV circuit whose normal operating voltages exceed the limits for an SELV circuit under normal operating conditions; and on 
which overvoltages from telecommunication networks and cable distribution systems are possible
IEC 60950-1, ed. 2.0 (2005-12)
tnv-3 circuit: tnv circuit whose voltages exceed the limits for a tnv-0 circuit under normal operating conditions; and on which overvoltages from telecommunication networks are possible
IEC 60065, ed. 8.0 (2014-06)
TNV circuit: circuit that is in the equipment and to which the accessible area of contact is limited and that is so designed and protected 
that, under normal operating conditions and single fault conditions (see 1.4.14), the voltages do not exceed specified limit values. A TNV circuit is considered to be a secondary circuit in the meaning of this standard.
IEC 60950-1, ed. 2.0 (2005-12)
tnv circuit: circuit which is in the apparatus and to which the accessible area of contact is limited (except for a tnv-0 circuit) and that 
is so designed and protected that, under normal operating and fault conditions, the voltages do not exceed specified limiting values
IEC 60065, ed. 8.0 (2014-06)
TNV circuit (including TNV-1 circuit, TNV-2 circuit, TNV-3 circuit): circuit that is in the equipment and to which the accessible area of 
contact is limited and that is so designed and protected that, under normal operating conditions and single fault conditions, the voltages do not exceed specified limit values
IEC 62102, ed. 2.0 (2005-05)
telecommunication network: metallically terminated transmission medium intended for communication between equipment that may be located in 
separate buildings, excluding: the mains system for supply, transmission and distribution of electrical power, if used as a telecommunication transmission medium; cable distribution systems; SELV circuits connecting units of information technology equipment
IEC 60950-1, ed. 2.0 (2005-12)
telecommunication network: metallically terminated transmission medium intended for communication between equipment that may be located in 
separate buildings, excluding: the mains system for supply, transmission and distribution of electrical power, if used as a telecommunication transmission medium; cable distribution systems; SELV circuits connecting units of data processing equipment
IEC 62102, ed. 2.0 (2005-05)
telecommunication network: metallically-terminated transmission medium intended for communication between apparatus that may be located in 
separate buildings, excluding the mains systems for supply, transmission and distribution of electrical power, if used as a telecommunication transmission medium; television distribution systems using cable
IEC 60065, ed. 8.0 (2014-06)
telecommunication network transient voltage: highest peak voltage expected at the telecommunication network connection point of the 
equipment, arising from external transients on the network
IEC 60950-1, ed. 2.0 (2005-12)
telecommunication network transient voltage: highest peak voltage expected at the telecommunication network connection point of the 
apparatus, arising from external transients on the network
IEC 60065, ed. 8.0 (2014-06)
SELV circuit: secondary circuit that is so designed and protected that under normal operating conditions and single fault conditions, its 
voltages do not exceed a safe value
IEC 60950-1, ed. 2.0 (2005-12)
SELV circuit: secondary circuit which is so designed and protected that under normal operating conditions and single fault conditions, its 
voltages do not exceed a safe value
IEC 62102, ed. 2.0 (2005-05)
service access area: part of the equipment, other than an operator access area, where it is necessary for service persons to have access 
even with the equipment switched on
IEC 60950-1, ed. 2.0 (2005-12)
service person: person having appropriate technical training and experience necessary to be aware of hazards to which that person may be 
exposed in performing a task and of measures to minimize the risks to that person or other persons
IEC 60950-1, ed. 2.0 (2005-12)
skilled person: person with relevant education and experience to enable him or her to avoid dangers and to prevent risks which electricity 
may create
IEC 60065, ed. 8.0 (2014-06)
skilled person: person with relevant education or experience to enable him or her to identify hazards and to take appropriate actions to 
reduce the risks of injury to themselves and others
IEC 62368-1, ed. 2.0 (2014-02)
instructed person: person adequately advised or supervised by a skilled person to enable him or her to avoid dangers and to prevent risks 
which electricity may create
IEC 60065, ed. 8.0 (2014-06)
instructed person: person instructed or supervised by a skilled person as to energy sources and who can responsibly use equipment 
safeguards and precautionary safeguards with respect to those energy sources 
IEC 62368-1, ed. 2.0 (2014-02)
RFT circuit (remote feeding telecommunication circuit): a secondary circuit within the equipment, intended to supply or receive d.c. power 
via a telecommunication network at voltages equal to or exceeding the limits for TNV circuits, and on which overvoltages from telecommunication networks are possible
IEC 60950-1, ed. 2.0 (2005-12)
RFT circuit; remote feeding telecommunication circuit: a secondary circuit within the equipment, intended to supply or receive d.c. power 
via a telecommunication network at voltages exceeding the limits for tnv circuits, and on which overvoltages from telecommunication networks are possible
IEC 60950-21, ed. 1.0 (2002-12)
RFT-V circuit: an RFT circuit which is so designed and protected that under normal operating conditions and single fault conditions the 
voltages are limited and the accessible area of contact is limited
IEC 60950-1, ed. 2.0 (2005-12)
RFT-V circuit: an rft circuit which is so designed and protected that under normal operating conditions and single fault conditions, the 
voltages are limited and the accessible area of contact is limited
IEC 60950-21, ed. 1.0 (2002-12)
RFT-C circuit: an rft circuit which is so designed and protected that under normal operating conditions and single fault conditions, the 
currents in the circuit do not exceed defined values
IEC 60950-21, ed. 1.0 (2002-12)
accessible: possibility of touching by the test finger according to IEC 61032:1997, test probe B 
IEC 60065, ed. 8.0 (2014-06)
accessible: touchable by a body part 
IEC 62368-1, ed. 2.0 (2014-02)
class i:  design in which protection against electric shock does not rely on basic insulation only, but which includes an additional safety 
precaution in such a way that means are provided for the connection of accessible conductive parts to the protective (earthing) conductor in the fixed wiring of the installation, in such a way that accessible conductive parts cannot become hazardous live in the event of a failure of the basic insulation
IEC 60065, ed. 8.0 (2014-06)
CLASS I equipment: equipment where protection against electric shock is achieved by using basic insulation and providing a means of 
connection to the protective earthing conductor in the building wiring those conductive parts that are otherwise capable of assuming hazardous voltages if the basic insulation fails
IEC 60950-1, ed. 2.0 (2005-12)
class I equipment: equipment in which protection against electric shock does not rely on basic insulation only, but that includes a 
supplementary safeguard in such a way that means are provided for the connection of accessible conductive parts to the protective earthing conductor in the fixed wiring of the installation 
IEC 62368-1, ed. 2.0 (2014-02)
class ii: design in which protection against electric shock does not rely on basic insulation only, but in which additional safety 
precautions, such as double insulation or reinforced insulation, are provided, there being no provision for protective earthing or reliance upon installation conditions
IEC 60065, ed. 8.0 (2014-06)
CLASS II equipment: equipment in which protection against electric shock does not rely on basic insulation only, but in which additional 
safety precautions, such as double insulation or reinforced insulation are provided, there being no reliance on protective earthing
IEC 60950-1, ed. 2.0 (2005-12)
class II equipment: equipment in which protection against electric shock does not rely on basic insulation only, but in which a 
supplementary safeguard is provided, there being no provision for protective earthing or reliance upon installation conditions
IEC 62368-1, ed. 2.0 (2014-02)
CLASS III equipment: equipment in which protection against electric shock relies upon supply from SELV circuits and in which hazardous 
voltages are not generated
IEC 60950-1, ed. 2.0 (2005-12)
class III equipment: equipment in which protection against electric shock relies upon supply from ES1 and in which ES3 is not generated
IEC 62368-1, ed. 2.0 (2014-02)

Non definitions - contained in IEC 62368-1 body text
ES  Electrical energy source

ES1  Electrical energy source class 1 (60 V, 2 mA d.c.)
ES1 is a class 1 electrical energy source with current or voltage levels not exceeding ES1 limits under normal operating conditions, and 

abnormal operating conditions, and single fault conditions of a component, device or insulation not serving as a not exceeding ES2 limits under single fault conditions of a basic safeguard. 
NOTE  ES1 may be accessible to an ordinary person. 

ES2  Electrical energy source class 2 (120 V, 25 mA d.c.)
ES2 is a class 2 electrical energy source where: both the prospective touch voltage and the touch current exceed the limits for ES1;
and under normal operating conditions, and abnormal operating conditions, and single fault conditions, either the prospective touch voltage 
or the touch current does not exceed the limit for ES2.
NOTE 1  ES2 may be accessible to an instructed person 

ES3  Electrical energy source class 3 (>120 V, >25 mA d.c.)
ES3 is a class 3 electrical energy source where both the prospective touch voltage and touch current exceed the limit for ES2.  
NOTE 1  The energy in ES3 may cause harmful physiological effects under contact with a body part. 
NOTE 2  Parts and circuits classed ES3 may be accessible to a skilled person, however, unintentional contact should be avoided.

ITU-T

TNV circuit: A circuit to which the accessible area of contact is limited and that is so designed and protected that, under normal operating and single fault conditions, the voltages do not exceed specified limiting values. TNV circuits are classified as TNV-1, TNV-2 and TNV-3 circuits.
Source : K.50 (00)
TNV circuit: A circuit in the equipment to which the accessible area of contact is limited and that is so designed and protected that, 
under normal operating conditions and single fault conditions, the voltages do not exceed specified limit values.
Source : K.64 (04)
TNV-1 circuit: A TNV circuit: - whose normal operating voltages do not exceed the limits for an SELV circuit under normal operating 
conditions; - on which overvoltages from telecommunication networks are possible.
Source : K.50 (00)
TNV-2 circuit: A TNV circuit: - whose normal operating voltages exceed the limits for an SELV circuit under normal operating conditions;
which is not subject to overvoltages from telecommunication networks.
Source : K.50 (00)
TNV-3 circuit: A TNV circuit: - whose normal operating voltages exceed the limits for an SELV circuit under normal operating conditions; 
on which overvoltages from telecommunication networks are possible.
Source : K.50 (00)
SELV circuit: A secondary circuit which is so designed and protected that, under normal and single fault conditions, its voltages do not 
exceed a safe value.
Source : K.50 (00)
telecommunication network: A transmission medium intended for communication between equipment that may be located in separate buildings.
ITU-T K.44 (05/2012)
telecommunication network: Entirety of equipment (comprising any combination of the following: network cable, telecommunication terminal 
equipment, and telecommunication system or installation) that are indispensable to ensure normal intended operation of the telecommunication system.
ITU-T K.72 (06/2011)
network cable: The cable infrastructure (transmission line) used to connect together telecom installations, systems and telecom terminal 
equipment. The network cable will normally end at a Network Termination Point (NTP). At this point, telecom terminal equipment or telecom systems or installations are attached. The network cable may also include in-premises extension cables or LAN cables.
Source : K.60 (03)
remote power feed: A remote power feed is a power feed provided by symmetric signal pairs or inner conductors of coaxial circuits 
simultaneously used for signal transmission. The supply of the operating voltage to customer terminal equipment is not a remote power feed.
Source : K.44 (03)
remote power feed: A remote power feed is a power feed provided by symmetric signal pairs or inner conductors of coaxial circuits 
simultaneously used for signal transmission. An example of a remote power feed is a remote feed telecommunication (RFT). Remote power feeds complying with the requirements for a TNV circuit are not classified as a remote power feed. The requirements for a TNV circuit are provided in [b-IEC 60950-1], a dedicated power feed (dpf) is defined in clause 3.1.7, and an RFT is defined in [b-ITU-T K.50].
ITU-T K.44 (05/2012)
RFT circuit: A circuit, other than SELV or TNV circuit, intended for the supply of power to equipment via a paired-conductor network, and which is so designed and protected that under normal operating and single fault conditions the voltages or currents do not exceed defined 
values. The circuit in the equipment that receives power from an RFT circuit is also considered to be an RFT circuit.
K.50 (00)
RFT-C circuit: A Remote feeding telecommunication circuit, that is so designed and protected that under normal operating conditions and 
single fault conditions, the currents in the circuit do not exceed defined values. NOTE – The current limit values under normal operating and single fault conditions are specified in ITU-T Rec. K.50 or IEC 60950-21.
K.64 (04)
RFT-C circuit: A current limited RFT circuit. The detailed characteristics of an RFT-C circuit are described in Annex B.
K.50 (00)
RFT-V circuit: A voltage limited RFT circuit. The detailed characteristics of an RFT-V circuit are described in Annex A.
K.50 (00)
RFT-V circuit: A Remote feeding telecommunication circuit that is so designed and protected that under normal operating conditions and single fault conditions, the voltages are limited and the accessible area of contact is limited. NOTE – The voltage limit values under 
normal operating and single fault conditions are specified in ITU-T Rec. K.50 or IEC 60950-21.
K.64 (04)
dpf, dedicated power feed: A dedicated power feed is a power feed provided by a dedicated cable which leaves the building.
K.44 (03)
dedicated power feed: A dedicated power feed is a power feed provided by a dedicated telecommunications cable which leaves the building and is used exclusively to provide the power feed. See clause 3.1.23 of ITU-T K.44
ITU-T K.44 (05/2012)

Telcordia/Ericsson

No relevant terms and definitions. Concepts and values are mainly in the body text.

ETSI

access network:part of a telecommunications network between the customer terminal installation and the first switching unit
EN 302 099 (2014-08) 
backfeeding or reverse powering: powering architecture that can supply power to access network units from the customer through its final distribution access copper pair
EN 302 099 (2014-08) 
distant power receiver:power equipment electrically connected to a Remote Power Unit
EN 302 099 (2014-08)
Remote Feeding Telecommunication (RFT) circuit:secondary circuit within the equipment, intended to supply or receive dc power via a telecommunication network at voltages equal to or exceeding the limits for TNV circuits, and on which overvoltages from telecommunication networks are possible
EN 302 099 (2014-08) 
Remote Power Unit (RPU):power unit, connected to the mains or froma centralized power plant, which supplies distant telecommunications equipment
EN 302 099 (2014-08) 
remote powering:power feeding of a telecommunications equipment by a remote power circuit 
NOTE:  Such a circuit consists of a remote power unit, distribution wiring, and fed receivers.
EN 302 099 (2014-08) 
RFT-C circuit:RFT circuit which is so designed and protected that under normal operating conditions and single fault conditions the currents in the circuit do not exceed defined values
EN 302 099 (2014-08) 
RFT-V circuit:RFT circuit which is so designed and protected that under normal operating conditions and single fault conditions the voltages are limited and the accessible area of contact is limited
EN 302 099 (2014-08)

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How far is Remote?

Remote powering implies that the power equipment is not local but some distance away. I asked some experienced colleagues, who helped create the ITU-T Recommendation K.50 (02/2000): Safe limits of operating voltages and currents for telecommunication systems powered over the network, the question "what does remote powering mean in terms of Remote Feed Telecommunication". I summarized their responses as follows:

The characteristics of Remote Feed Telecommunication are:

  • Remote means that the powering and powered equipment are in separate buildings (external feed) or at different external locations in cabinets.
  • Remote can also be expressed as the powering and powered equipment do not share a common earth point.
  • RFT voltages exceeds the limits for TNV CIRCUITS or in hazard speak exceed ES2 voltages(=ES3) (The IEC 60950-21 scope is "This part of IEC 60950 applies to information technology equipment intended to supply and receive operating power via a TELECOMMUNICATION NETWORK, where the voltage exceeds the limits for TNV CIRCUITS.")
  • These high voltages automatically means that users be prevented access to RFT voltages.