Power Over Ethernet: Does 1 Cord Fit All?
By Steve Surfaro
One of the main benefits of IP technology — from routers to VoIP phones to network cameras — is the ability to deliver power and data from one cable: the Ethernet cable. This eliminates additional wiring and cable pulling while saving installation time and adding convenience. But before sending the electrician home, there are a few things to note about power over Ethernet (PoE) standards.
First, if you’re using quality Ethernet cable connected to a PoE switch, you need to confirm that the device being powered — such as a network camera or access control reader — can accept and use Ethernet power for operation. As a safety precaution, PoE switches or power source equipment (PSE) devices such as mid-spans and splitters won’t send power over an Ethernet cable if it’s not connected to a PoE-compliant device.
Second, check the wattage rating of the network switch as well as the power requirements of all devices being powered by that switch. The PoE standard (IEEE 802.3af) has a maximum power output of 15.4 watts per port, or 12.95 watts to the powered device after factoring in normal power loss that occurs on a twisted pair cable for the max run of 100 meters.
In 2009, a new Hi PoE standard (IEEE 802.3at or PoE+) was ratified that can deliver 25 watts of power per port or 22.55 watts to the powered device after cable power loss. If a Hi PoE network switch uses all four of the twisted pairs in the Cat-5e or AC6 cable, it can deliver up to 30 watts and eventually even 51 watts of power per channel. This is more than sufficient to power and control pan/tilt/zoom (p/t/z) network cameras as well as heaters and fans in outdoor network cameras over a single Ethernet cable.
If you don’t match the power specifications of your PSE switches with your devices, you will not deliver the necessary power for those devices to function. Simply add up all your devices’ power requirements, make sure the PSE is providing multiple power supplies and backup where fault tolerance is required, and then connect with confidence.
Steve Surfaro is Business Development Manager and Security Industry Liaison for Axis Communications Inc.
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Power over Ethernet
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