Myths about Power Over Ethernet
 April 27, 2008
Power-over-Ethernet (PoE) technology integrates power and data across standard 
Cat5/5e/6 network cabling and provides more flexibility in today’s workplace. 
PoE enables power to be supplied to network devices, such as IP phones, network 
cameras, and wireless access points through a single, most often existing, 
network cable. When combined with an uninterruptable power supply (UPS) a PoE 
network delivers continuous operation and minimizes business downtime by 
eliminating most power interruptions. With the ability to install endpoints in 
any location PoE technology provides a scalable and flexible networking 
infrastructure geared for growth and efficiency.

 
 PoE Switches can provide all the power I need or will need.
Today most switches are merely PoE-enabled.  This means the majority rely on 
power management to share available power across the switch ports. The switches 
are designed with a smaller power supply that is typically capable of powering 
the switch itself and providing the required 15.4 watts of power over a limited 
number of ports. 
For example:  A 24-port PoE Switch with power management typically has a 
195-watt power supply. After the 40 watts needed to power the switch, you have 
approximately 155 watts remaining. If 12 of the 24 ports are used to connect 
end devices using 11.5 watts each, you would only have 17 watts remaining to 
provide power on the last 12 ports.  The math doesn’t match the ports: 195W – 
40W (switch) – 138 (12 devices @ 11.5W/ea) = 17W left for power on 12 ports 
Myth Busted: A PoE Switch is often not the best and most cost effective 
solution.
 
  
 A midspan and a PoE switch are the same.
A PoE Midspan is not a switch.  A Midspan is an additional PoE power source 
that can be used to offer full power to all endpoint devices.  PoE Midspans 
(Power Hub or Power Injector) pass data from a switch and ‘inject’ safe power 
acting as a patch panel of sorts.  Midspans are commonly used with either a 
non-PoE switch, an existing PoE switch, or a new PoE switch in a network. In 
addition to offering full power across all available ports, midspans costs 
substantially less per port and overall than a new PoE enabled switch.
Myth Busted: Midspans do not switch – they make use of existing best-in-class 
switches.  They inject safe power across all ports and cost less than PoE 
switches. . 
  
 Only a switch that has PoE built in should be used to power devices like IP 
Phones, Access Points, and IP Security Cameras. 
Switches were designed to, well, switch.  PoE Switches are designed with power 
management and have to distribute different power as required to ports but 
there is often not enough power for all devices plus the power required to 
complete the primary task - switching.  Networks that have multiple devices 
like IP phones, IP cameras, wireless access points quickly go beyond the 
limited capacity of managed power PoE switches.  As more PoE devices continue 
to grow in capabilities and market share this managed power limitation will 
become more and more evident.  Midspans, in contrast to switches, were designed 
to provide full power on every port and deliver safe and reliable power based 
on the industry standards (IEEE802.3af/at). 
Myth Busted: Rather than relying on power management in a switch use a midspan 
that can deliver full power (15.4W) to every port for all PoE-enabled devices 
now and in the future.   
  
 Ethernet devices not PoE-enabled (non 802.3af/at compliant) cannot be powered 
using PoE technology. 
Many devices do not directly accept Power-over-Ethernet but can still use PoE 
technology. If the device uses less than 12.5 watts (802.3af) or less than 50 
watts (802.3at+) and connects to an IP Ethernet network you can use a PoE 
splitter.  PoE splitters enable you to accept PoE power from any IEEE 
802.3af/at compliant switch or midspan then separates the data and power on to 
two seprate cables.  The data is connected to the end device through a standard 
RJ45 plug while the power is connected using a standard 5.5 x 2.1 x 12mm 
Adapter Plug.  Splitters can also convert the input voltage to the required 
voltage for a non-PoE device. Splitters are traditionally used with older 
network products which only accept power through their (DC) jack and data 
through their RJ-45 jack.
Myth Busted: PoE splitters can be used in conjunction with PoE midspans and 
switches to provide both the data connectivity and power required by most 
endpoint devices. 
  
 I need/will need additional PoE switch ports to power my IP cameras and 
high-power pan, tilt, and zoom (PTZ) cameras. 
Today, many devices have evolved into more advanced solutions with higher power 
requirements. The traditional approach was to endure a “forklift upgrade”. This 
meant buying new PoE switches at considerable cost and physically swapping out 
the existing switches to meet higher power requirements or add more powered 
ports. There is an easy and more cost-effective way – separate the data and 
power in the wiring closet (IBF). It is more efficient and costs less to 
separate your data and power allowing you to keep your best-in-class business 
switch for your IP needs and supplement it where required with best-in-class 
midspan technology to power the endpoints. 
Myth Busted: A PoE Switch is often not the best and most cost effective 
solution. 
  
 All midspans are created equal . . . they are all the same. 
Always select a best-in-class midspan. If you wanted to enhance your switched 
network wouldn’t use a best-in-class network switch?  Of course you would. A 
midspan designed and manufactured by a leading power supply company that 
understands power, power requirements, and one that delivers enterprise-level 
solutions. 
Select a midspan manufacturer that has multiple members on the IEEE (PoE) 
committee helping to define safe, new PoE standards. This ensures that every 
midspan is designed to meet current and future IEEE specifications for 
Power-over-Ethernet. 
Select a midspan manufacturer that designs, manufactures, and tests its own 
product rather than outsourcing these tasks across the globe to cut costs.
Select a midspan that has a high-speed, common interface to access the 
management console. A USB port is not as cheap as a serial port (RS-232) but is 
faster, more user-friendly, and more common on high quality midspans. 
Myth Busted: Although there are many midspan manufacturers out there, few have 
the power supply experience, quality controls, and manufacturing capability to 
produce best-in-class midspans.  All midspans are NOT created equal.  
  
 
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