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Power Over Ethernet
Last Updated: 01/31/2017

Description:

Power over Ethernet (PoE) refers to the use of an Ethernet cable to transmit electrical power to a remote device that does not have access to an AC power outlet.

Application:

Used to power devices through the same structured cable as data at the same time the data is being transmitted. Often used with devices such as IP phones, wireless access points, digital signage and IP security cameras. Also used with LED lighting.

Installation Considerations:

Wire gauge and type of conductor material used is very important. It is recommended that 24 gauge copper be used for 15.4 watt and 25.5 watt PoE. 23 gauge CAT6A is being recommended for proposed higher watt standards.

The 802.3 standard states that distance is limited to a maximum of 100 meters (328 Ft.).

Maximum bundle size depends on conductor gauge. 28 gauge cable should be limited to 48 cables per bundle up to 600mA and 24 cables up to 960mA. 24 gauge cable should be limited to 100 cables per bundle up to 600mA and 61 cables up to 960mA. 23 gauge cable is rated for 100 cables per bundle for both 600mA and 960mA.

Bundle temperature should not exceed 15 degrees Celsius (59 Fahrenheit) over ambient air temperature. Care must be taken with bundled cable running in conduit. It may be necessary to reduce the bundle size in this environment to keep the temperature under the 15 degree rise.

Arcing will occur when a plug is removed from a device with live PoE causing damage to both connector and port. Use plugs and jacks designed to negate the arcing damage by restricting it to a part of the plug/jack where the damage will not affect performance.

Common Options:

  • 802.3af PoE (up to 15.4 watts)

  • 802.11af PoE+ (25.5 watts)

  • Proposed 802.3bt type 3 PoE++ (51 watts)

  • Proposed 802.3bt type 4 PoE++ (71 watts)

  • (The higher powered 802.3 standards will offer enough power to work with such devices as pan/tilt/zoom IP cameras.)

  • HDbaseT (71 watts) - audio/video standards used for digital signage and teleconferencing applications

Popular Manufacturers:

Related Industry Terms/Acronyms:

  • mA (milli-Ampere) – a measurement of electrical current

  • Cable insertion loss (as it relates to PoE) - signal loss within a continuous path associated with temperature rise

  • Arcing (as it relates to PoE) - electrical current discharge resulting when a current jumps a gap between contacts in a plug and/or jack

  • Operating temperature - refers to the operating temperature range of a cable which must be considered in relation to the temperature rise of a PoE cable bundle. CAT5E and CAT6 typically operate at a maximum of 60 degrees C (140 F)

  • Endspan PoE - refers to a network switch that provides power through one or more ports

  • Midspan PoE - refers to an in-line PoE injector

Comparison Chart:

Standards Max. Current Number of Energized Pairs Power at Device
PoE IEEE 802.3af 350mA 2 13 W
PoE+ IEEE 802.3at Type 2 600 mA 2 25.5 W
PoE++ Proposed IEEE 802.3bt Type 3 600 mA 4 51 W
PoE++ Proposed IEEE 802.3bt Type 4 1000 mA 4 71 W
HDBase-T HDBase-T 1000 mA 71 W

(Chart reproduced, in part, from ICT Today, Volume 37, Number 2, March/April 2016)

See Also:

  • PoE injector – injects power into an Ethernet line
  • PoE switch – network switch with ports that function as a PoE injector
  • PoE splitter – splits PoE power and data on an Ethernet cable from a PoE device, allowing power to be applied to an Ethernet enabled, non-PoE remote device

Further References:

  • www.hdbaset.org
  • BICSI (Building Industry Consulting Services International)
  • IEEE (Institute of Electrical and Electronics Engineers, Inc.)
  • ANSI (American National Standards Institute)
  • TIA (Telecommunications Industry Association)
  • ISO (International Organization for Standardization)

FAQs:

What kind of cable is used for PoE?

Category 5E or higher constructed with 100% pure copper. Beware of low price category cable that may use copper-clad aluminum which has a much higher DC resistance than pure copper. Higher resistance = higher heat and less power.



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