compatible with the PSE. When a PD is connected to
the PSE, power is generated only when a compatible PD
detection is found. The PSE discovers how much power
the PD is required to draw. The PSE then monitors the
power draw and can disconnect the circuit if the PD
exceeds a set limit or if the PD is disconnected.
There are four “Types” of power delivery over
Ethernet as defined by IEEE standards and specifications
(see Table 1). Type 1, which was ratified in 2003,
addressed a low range of 4 to 15.4 W at the PSE and up to
13 W at the PD (depending on the distance and voltage
drop) and is often informally referred to as “802.3af.”
Type 1 was created to address digital security cameras
that were utilizing balanced twisted-pair cabling to
connect to an IP network and delivered power over two
of the unused pairs. Type 2, which was ratified in 2009,
addressed the power needs of more complex security
cameras (e.g., pan, tilt and zoom) and delivered up to 30
W DC at the PSE and up to 25.5 W at the PD. Type 2 is
often referred to as “PoE Plus.” The newly ratified Type 3
and Type 4 use all four pairs of a balanced twisted-pair
cable to push PoE to 60 W and above. Therefore, they are
often referred to as “4-pair PoE.” Because the standards
January/February 2019 I17
is to understand how this will change the ICT cabling
landscape and installation practices. The “nice to know”
is that there are published standards and codes available
to help guide the planning and installation for these
higher power PoE deployments. Also, it is always a “nice
to know” that manufacturers of cabling systems and
devices can provide training and design options. But
even though there are infrastructure standards for the
cabling, there are no specific standards or protocols for
the individual devices (e.g., LED lights). It is still a “wild,
wild West” as implementation topologies vary among
system and device manufacturers.
THE POWERS THAT BE
To deliver PoE, there must be a power source and a
PoE-enabled device to receive the power. The power
sourcing equipment (PSE) can deliver a variety of power
levels, depending on the requirements of the powered
device (PD). All the powering takes place in the network’s
Ethernet link layer, which differs from plugging a device
into an AC outlet.
It is important to understand these different types
in the selection of powered devices, which must be
Power over Ethernet
Standard
(Type 1) IEEE 802.3af-2003 15.4 W 13.0 W 2-pairs 350 mA
TABLE 1: Overview of power types by IEEE standards.
Minimum
Power at PSE
Output
Maximum
Power at PD
Input
Number of
Pairs
Maximum
Current per
Pair
Power over
Ethernet Plus
(Type 2)
4-pair PoE
(Type 3)
4-pair PoE
(Type 4)
IEEE 802.3at-2009
IEEE P802.3bt-2018
IEEE P802.3bt-2018
30.0 W
60.0 W
90.0 W
25.5 W
51.0 W
71.3 W
2-pairs
4-pairs
4-pairs
600 mA
600 mA
960 mA