PoE (Power Over Ethernet)

Question List

Difference between Passive PoE and Active PoE/PoE+ (IEEE 802.3af/at)?

  • Passive PoE , also known as “always ON”. Power is delivered immediately without negotiation.
  • IEEE 802.3af/at (Active PoE, PoE+) , standardized solution where power is delivered from power source equipment after a negotiation with powered device.

Here is detailed comparison between Passive PoE and Active PoE 802.3af/at:

PoE 802.3af/atPassive PoE
Related cost*MediumLow cost*
Max. cable distance100m100m
Power InjectionAfter Negotiation


Ethernet Support10/100/1000 Mbit/s10/100 Mbit/s (Injected pairs + 4,5 and -7,8)
Standard802.3af/atN/A, use by some vendors such as MikroTik or Ubiquity
Robust Against Wrong CablingYesNo. Only Anchor device can be connected into PoE socket!
Never connect to PC or another network device.

*Please consider RTLS deployment with tens of anchors. The network PSE devices with single Active PoE have usually fractional price of Active PoE with multiple devices. While Passive PoE injectors requires no electronics, so they are very affordable for single or multiple port injections.

Differences in the PoE technologies described in more detail.

  • IEEE 802.3af/at – standardized solution – this prevents of unwanted hazards in cases where cable is damaged or attached to non PoE device. This standard is heavily supported by network vendors such as Cisco. The IEEE 802.3af (PoE) standard supports the delivery of power over Ethernet up to 15.4W per port. The IEEE 802.3at (PoE+) standard supports up to 25.5W of power on the ports, which allows the use of devices that require power more than 15.4 W.
  • Passive PoE – always ON” – basically, it is direct voltage injection into unused Ethernet wire pairs, positive (+) 4,5 and negative (-) 7,8. This provides very simple, flexible and cost-effective solution for powering anchor devices. However, technician must be careful and connect “power” cable only to PoE supported device. This technique is supported by vendors: Ubiqua or Mikrotik. Sewio recommends using a 48V PoE power supply for cables longer than 50m.
    Important note: When using Passive PoE, always use power source for Passive PoE injector with galvanic isolation and short protection.

How do I find out if the PoE power source is sufficiently dimensioned?

We recommend to use 48V adapter for PoE Injector (see anchor’s datasheet), to minimize voltage drop among the long cables. Since anchor consume just 2.5W roughly 50mA current rating is enough to power-up the anchor. For multiple anchors, just multiply 2.5W with number of anchors + allocate some power budget reserve.

If you would like to calculate voltage drop among the cable length, you can find some PoE calculators below:

Besides cable length, you would need to know some other cable parameters (AWG – American Wire Gauge, DCR – Direct Current Resistance, etc.) which directly affects the voltage drop.

How should I use Passive PoE? / How to implement Passive PoE in network infrastructure?

There are several options to deploy Passive PoE in network infrastructure:

  • Single port Passive PoE Injector
  • Multiple port Passive PoE Injector
  • Network switch with Passive PoE support
  1. Single port Passive PoE Injector + power source
      LAN Socket – connect to network switch or computer
      POE Socket – connect to Anchor
      Power supply connector – connect the PoE power supply
  2. Multiple Passive PoE port Injector + power source
      LAN Socket – connect to network switch or computer
      POE Socket (Power+Data) – connect to Anchor
      Power supply connector – connect the PoE power supply (back side)

    RULE 1: Always use power source for Passive PoE injector with galvanic isolation and short protection. Verified PN: Mean WELL GS36E48-P1J.
    RULE 2: Be careful during PoE cable manipulating: The Ethernet cable from PoE socket marked as PoE or sometimes “Power + Data” should be considered as “live” and only ever plugged into the anchor device.
  3. Network switch with Passive PoE
    Many manufacturers on the market offer switches with Passive PoE support. One example of such a switch is Ubiquiti Edge Switch.

How to extend cable to Anchor to more than 100 m without additional power supply?

PoE Passthrough (sometimes depicted as PoE In/PoE Out) is an approach where small PoE extender unit can provide PoE input and several PoE Outputs without required external power adapter. This enables to prolong cable distance from network switch to anchor to several hundred meters.

One should always consider voltage drop among the cable once the anchors are daisy chained. Anchor consume maximally 2.5W. Here is a cable length calculator.
The second thing that need to be considered is what type of the PoE is used – Passive PoE or Active PoE?

There are different PoE Passthrough extenders for Passive PoE and (Active) PoE IEEE 802.3af/at.

What type of the PoE support individual types of anchors?

The table lists the PoE versions that are supported by individual types of Anchors.

Anchor NamePoE Support
Anchor 1.3Passive PoE 24-48V*
Anchor 1.4Passive PoE 24-48V*
Anchor 2.0 Passive PoE 48V-56V*
PoE 802.3af/at
Anchor VistaPassive PoE 48V-56V*
PoE 802.3af/at

*When using Passive PoE, always use power source for Passive PoE injector with galvanic isolation and short protection. Sewio recommends using a 48V PoE power supply for cables longer than 50m.

Will Anchor 1.4 work with PoE Switch 802.3af/at?

Anchor 1.4 will NOT work natively with standard PoE 802.3af/at since it supports Passive PoE only.

There are three options:

a) Preferably use switch without PoE, equipped with Passive PoE Injector + 48V Power Source.

b) Disable PoE ports on the PoE Switch and add Passive PoE Injector + 48V Power Source.

Read more here. PoE injector and power source equipment can be provided by Sewio.

c) Use Active PoE to Passive PoE converter per port, can be found here.