Remote Powering over communications cabling (part 1)

Remote powering implies that the power equipment is not local but some distance away. It is an alternative to commercial power, which can be hard to get and/or expensive. Remote means that the powering and powered equipment are in separate buildings or at different external locations inside same building.

Line powering is a way to power remote equipment from a central location using existing cable pairs in the copper network. It has applications such as fiber-to-the-node (FTTN), fiber-to-the-home (FTTH), DSLAM powering and powering cell phone network base station components. Remote powering is also used in cable TV network and distributed antenna systems (DAS).

Remote powering over communications cabling is not something new. Line power has been used as far back as the early 1960s by Telcos for T1 power and then HDSL powering and more recent DSLAM powering.

Power over Ethernet (PoE)

Power over Ethernet term describes several standard or ad-hoc systems which pass electric power along with data on twisted pair Ethernet cabling. This allows a single cable to provide both data connection and electric power to devices such as wireless access points, IP cameras, and VoIP phones. Recently communications technologies (ICT) industry has seen an array of PoE-enabled devices and applications proliferate commercial buildings, such as Wi-Fi, surveillance cameras, commercial lighting and sensors. 

PoE Switching explanation by NETGEAR (international version)

There are several common techniques for transmitting power over Ethernet cabling. IEEE 802.3 has since 2003 standardized several versions of the standard with different power ratings. They allow feeding power up to 100 meters of normal twisted pair Ethernet cabling infrastructure (CAT5, CAT5e, CAT6, etc.). Typically 15 or 30 watt variations used. Current IEEE standards can handle maximum power up to 30 watts and non-standardized solutions up to 60 watts. This power is already enough to enable IoT LED lighting to be powered through the data cabling. New IEEE 802.3bt standard that will be completed in 2018 will increase maximum power to almost 100 watts. POE is a well defined standard that can feed feeds typically 48V DC (max 57V) voltage to Ethernet wiring when there is a device that need that power connected. The power is fed to the cable between two wire pairs on the Ethernet connection (in 10/100 Mbit/s Ethernet power can be the data carrying or free wire pairs, in 1G Ethernet power and data always share same wire pairs).

The IEEE 802.3 LAN/MAN standards committee has approved a number of PoE standards:

  • IEEE 802.3af-2003 – Provides up to 15.4 watts of DC power (PSE), 12.95 watts at load (PD), current 350 to 400 mA
  • IEEE 802.3at-2009 – PoE standard also known as PoE+ provides up to 30 watts of DC power (PSE), 25.5 watts at load (PD), current 600 milliamps

Development is underway to increase the available power to the PD to 70 watts, which is being led by the IEEE P802.3bt DTE power via MDI over 4-pair task force.

The power that can be fed to Ethernet cable is is considered safe compared to normal mains power. Class 2 power limits are defined within the United States National Electrical Code (NFPA 70), which states that Class 2 circuits have voltage limitations not exceeding 30VAC or 60VDC with a maximum power output of 100VA.  Due to its power limitations, a Class 2 circuit is considered safe from a fire initiation standpoint and provides acceptable protection from electrical shock

PoE also meets the specifications of Safety (or Separated) Extra Low Voltage Power (SELV) defined within IEC 60950-1, which is an international standard for IT equipment. SELV circuits meet the following criteria: Extra Low Voltage Circuit (< 35 VAC, <60VDC), low risk of accidental contact with a higher voltage primary circuit and typically involves an isolating transformer. All power sourcing equipment (PSE) conform to IEC 60950-1:2001 and be classified as a Limited Power Source (LPS) carrying no more than 100 volt-ampere (VA) per port without the need for special over-current protection devices.

Power over HDBase-T (PoH) specification, developed by the HDBase-T Alliance calls for 95 to 100 watts of power over twisted-pair cabling. It is used for transporting video signals and power to remote monitors and displays in buildings.

TV antenna wiring

In addition to AC power there are local (within one building) applications where some low power DC is fed through the antenna cabling from the power supply to antenna amplifier. Using coaxial cables to deliver power to small-scale electronics is a common engineering practice. Typically the outer shield of coax cable is used as negative end of supply. Very many TV cable amplifiers (usually located on attic) use this method of delivering DC and antenna signal over a single coax cable.

Most typical power supply voltage used for this are 12V DC The power is inserted to the cable using DC power inserter. The available power is quite low (typical value around 12V 100 mA).

Typical satellite TV setup operates at voltages between 13V and 18V DC on the antenna cable.

24 DC is used for powering large house common antenna TV amplifiers.

Some set-top box devices and GPS receivers supply current limited 5V DC for the active antenna.

Cable TV

Using coaxial cables to deliver power electronics is a common engineering practice. The majority of the cable TV systems around the world use AC power supplies that provide conditioned and regulated 60 or 90 Volts AC to the active devices in the field. The power supplies take the local electric power (117 VAC 60 Hz in the US and 220-240V AC 50 Hz in Europe) and step it down to either 60 VAC or 90 VAC which is what amplifiers are designed to operate on. The cable power supplies then by using a power inserter, put the 60 or 90 volt power on the cable system coax cable.Traditionally the power has came from mains power supply so is same frequency as mains power. It seems that 60V AC 50/60Hz is most common, because in USA for the portion of the CATV plant which is within a multiple dwelling unit (MDU), the restrictions of the safety codes limit voltages to 60V. A power supply with a 15-A rated output current is by far the most common size of power supply

The cable causes some voltage drop that – the resistance per kilometer of coaxial cable can vary from 0.5 to 3 Ohms/Km (typical values).
In addition to powering CATV amplifiers, the remote power can also be used to power other communications equipment connected to cable TV networks. The Remote PHY technology creates major opportunities for operators who wish to take a quantum leap to networks with substantially higher capacity. Some DOCSIS 3.1 Remote PHY device (RPD) for example can be powered fr0m cable TV power. With this kind of setups it is common to use standby power supplies thet use batteries to provide CATV powering waveforms which are completely unaffected by
utility outages. A power supply with a 15-A rated output current is by far the most common size of power supply.

Cable Television Node

CATV Power Supply

Information sources:


  1. Tomi Engdahl says:

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  4. Tomi Engdahl says:

    Electrical Energy related hazards
    – Hazardous energy level:
    240VA or more for 60 s or more, or
    Stored energy of 20J or more, at a potential of 2V or more

    Fire hazards
    – IEEE802.3af addresses this issue by requiring ports to comply with
    the requirements for a Limited Power Source (LPS), i.e., <100W
    (Sub-clause 2.5 of IEC 60950-1)
    POEplus standard should keep LPS requirement too.
    – Protection of the telecommunication wiring from overheating and
    catching fire is achieved by limiting the max current (Sub-clause
    6.3 of IEC 60950-1).
    The maximum current should not exceed a current limit for
    specific wire gauge.
    The current limit is 1.3A if such wiring is not specified.


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