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

You are here:
  • 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/at Passive PoE
Related cost* Medium Low cost*
Max. cable distance 100m 100m
Power Injection After Negotiation Immediately
Ethernet Support 10/100/1000 Mbit/s 10/100 Mbit/s (Injected pairs + 4,5 and -7,8)
Standard 802.3af/at N/A, use by some vendors such as MikroTik or Ubiquity
Robust Against Wrong Cabling Yes No. 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.