PoE : What does it mean to IT Xpert?

Power over Ethernet or PoE technology describes a system to safely transfer electrical power, along with data, to remote devices over standard category 5 cable in an Ethernet network. It does not require modification of existing Ethernet cabling infrastructure.


The IEEE 802.3af PoE standard provides up to 15.4 W of DC power (minimum 44 VDC and 350 mA) to each device. Only 12.95 W is assured to be available at the powered device as some power is dissipated in the cable.

Is it dangerous to transmit so much power over Ethernet?

I looked around and found a recent article in which TMC.net interviewed Amit Gattani, Director of Marketing for Akros Silicon. According to Akros Silicon’s Web site, the company was actively involved with drafting the new 802.3at standard.

Gattani noted that 13W solutions will require only Cat 5 cable while 30W solutions will need Cat 5e and above. The reason, he says, is that “Cat 5e and above have lower resistance drops so the heating issue is less.” Pertaining to concerns about the dangers of overheating, Gattani told TMC.net, “The 30W power limitation is actually put in place for a high degree of safety margin from the cable bundle heating up.”

So while the probability of PoE-powered Ethernet cables heating up is there, it should not pose a problem in most instances.

Impact on cooling and energy consumption

Will the use of PoE change the dynamics of the data center or server room in terms of energy consumption? I had the opportunity to interview the top executives of Chloride Powers on their stopover in Singapore last week and posed this question to them.

Etienne Gurou, Vice President of Chloride South East Asia, took the question. He pointed out that ultimately, the energy consumption remains similar — less some power loss on the wire of course — regardless of how it gets there. As such, what needs to be attended to would be issues pertaining to the ventilation and cooling of the slightly warmer cables or the powered hardware rather than any actual re-architecture of the datacenter.

Conclusion

When all is said and done, the ratification of the more advanced IEEE802.3at standard is hardly earth shattering. However, the increased maximum power can only mean a wider range of applications that will eventually be possible and, ultimately, the increased deployment of PoE on the whole.