The ABCs of PoE
Integrators have a real advantage with increased installation flexibility and lower labor cost
- By Richard L. Malstrom
- Sep 01, 2014
With the introduction of IP cameras, system integrators have
experienced big improvements in the quality and performance
of video systems that can be offered to their customers.
Networking technology, however, requires integrators
to learn new terminology and methods in designing and
installing an efficient and reliable system.
One area of this technology that is proven to provide a real benefit is PoE.
What is PoE?
Power over Ethernet is an extension of the same concept used in the telephone
industry, where voice and power are applied to the same cable. The 48VDC voltage
used in plain old telephone service (POTS) analog circuits is what is commonly
used for today’s PoE systems. In fact, the first standard adopted by the Institute
of Electrical and Electronics Engineers (IEEE) came from a well-known telecommunications
company’s research division.
Currently, there are two standards approved by the IEEE. The first, approved in
2003, is IEEE 802.3af and specifies up to 15.4 watts of direct current (DC) power.
The second standard, ratified in 2009 as IEEE 802.3at, is commonly called high
power PoE (HPoE) or PoE+ and doubles the power capabilities to 30 watts. Both
standards have a maximum distance of 100 meters (328 feet) that is dictated by
the distance limitation of Ethernet network cable. This standard is designed to be
plug-and-play; however, there are some caveats to be aware of.
A basic PoE-based system consists of three main components:
- Power-sourcing equipment (PSE), such as a PoE network switch.
- Category network cable.
- A remote-powered device, which may be an IP camera, IP access panel,
IP intercom, VoIP or wireless access point (WAP).
Power-sourcing equipment is a device that injects power onto the same network cable
that is being used for data. The injector can be a stand-alone single-port or multiport
device, or the injector can be built into a network switch. The second option
is more common today due to the convenience of using a single integrated device.
The network switch is the heart of an IP video system. The data from IP cameras,
NVRs and video management systems (VMS) streams all travel through the
switch. Therefore, a high-performance switch with a non-blocking high-bandwidth
switch fabric is certainly an important consideration in network design.
Integrators using PoE technology need to understand that the PoE switch is not just
handling data transmission, but also serving as the centralized power source for the
video surveillance system. Selecting a PoE switch with sufficient power capability is
critical in designing an efficient and reliable power grid for powered devices.
Although PoE is primarily designed as a plug-and-play technology, not all
PoE switches are designed to deliver the full demands of maximum PoE on each port. PoE switches are sold at different
price points, and it’s easy to make
a purchase decision based on the lowest
price. The cheaper PoE switch will
typically have a less robust power supply
and may not provide the full power
required by PoE endpoints.
PoE uses the same category network
cable that is used for data. A category
cable has four pairs (eight wires) inside,
with two of the pairs used for data,
leaving the open two pairs to be used
When planning power needs, take
into account power loss due to voltage
drop on the cable. To help understand
the specified power at the switch versus
what is available at the endpoint, let’s
look at the IEEE802.3 PoE standards
(which are shown above in Table 1):
The security industry is accustomed
to working with 12VDC/24VAC voltages,
and sometimes integrators want to
use their existing analog power supplies
or don’t understand why 48-56VDC is
required for PoE devices. Since the wire
gauge in PoE category cables is smaller
than those typically used for analog
power, a higher voltage is needed for
two reasons: to overcome a greater resistance
and to limit the current flow.
If enough voltage isn’t injected at the
source to overcome the increased resistance/
voltage drop, then there won’t be
sufficient power at the PD end. At the
same time, with too much current flowing
in the cable, there’s a potential fire
safety hazard due to the possibility of
the cable overheating.
When selecting a PoE switch, it’s important
to understand the power requirements
of the endpoint PDs and to select
a switch that has sufficient power to
meet the total demands of the system.
Just about any PoE switch will state
on the box that it “supports up to
15.4W per port” (or 30W for PoE+).
But, the key PoE switch specification to
review is the switch’s “total power budget”
Even a switch with a limited power
budget can provide up to 15.4W per port,
but the actual total number of ports that
the switch can provide full power to
may be limited based on the total power
consumed by the powered devices. That
means the switch may not have enough
power to meet the demand of all ports.
For example, an eight-port switch
may correctly claim to provide up to
15.4W of power per port, but have a
total power budget of only 70W. The
maximum number of ports for which
the switch could provide a full 15.4W
of power would be about four ports.
Since many small form factor IP cameras
operate at around 4 to 6 watts, a
PoE switch with the above power budget
configuration may work initially,
but if higher-powered cameras using
infrared LEDs or PTZ control, or require
an enclosure, heater or blower
are added, the power budget may become
insufficient. Customers won’t
understand why portions of their
IP video system go down each night
when the newly added infrared cameras
Advantages for Integrators
Security integrators gain significant
benefits from PoE through increased
installation flexibility, lower labor cost
and improved reliability. For example,
since the power is remotely distributed
from the network PoE switch, the need
to consider an IP camera’s proximity to
an AC outlet is eliminated. This allows
increased installation flexibility while
lowering installation and labor costs
by reducing or eliminating the need
to subcontract an electrician to install
AC electrical outlets. Some real-world
examples of this are as follows:
- The CTO of a U.S.-based healthcare
system estimated that he saved
$600,000 in setup costs by installing
200 access points powered by PoE
instead of 110-volt AC outlets in his
company’s hospitals; and
- a university in Indiana installed
1,100 wireless access points powered
by PoE, saving $350 to $1,000 per
installed access point by eliminating
labor costs incurred from contracting
an electrician to run wiring for
new AC outlets.
Also, using a managed PoE switch
allows the integrator to have complete
control of operation, power management,
monitoring, scheduling and diagnostics—
either locally or through
remote access. Some switches can detect
if an IP camera locks up and will
remotely power cycle PoE to reboot the
camera, eliminating a service call for
the event. If the condition continues to
reoccur, the switch can send an email
notification to the integrator that service
may be required. Add an uninterruptable
power supply (UPS) to power
the PoE switch in the event of a power
failure, and you have a resilient IP surveillance
system to offer your customer.
This helps maximize profits on any service
agreements in place.
As the industry continues to change, so
does its demand for more power. Reports
estimate that there will be 125 million
PoE ports by 2017, with many devices
exceeding the current 2009 standards.
Some vendors are already experimenting
and offering PoE products
providing up to 60 watts of power. This
is accomplished by utilizing all four
pairs in a Category 5e cable, which is
currently not supported by the 2009
standard. However, choosing products
that adhere to the IEEE standards can
help minimize potential issues.
The IEEE committee is working on
its next standard—intended to inject
up to 60W of power with an available
49W of power at the endpoint. This
will address the need for higher power
as more uses for PoE technology to remotely
power various devices are created.
This extra power will come from
tested and standards-approved use of
all four pairs in a Category 5e cable;
but, to minimize the heat generated by
this extra power, Category 6 cabling
may be required.
This article originally appeared in the September 2014 issue of Security Today.
Richard L. Malstrom is the product marketing manager, transmission, for Interlogix.