Power, PoE & BTUs

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Oct 25th, 2007
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I'm trying to figure the true number of BTU's that a 3750E-48PD-F puts out. Cisco lists in two separate documents that the max BTU/hr for this device is 3939 (http://www.cisco.com/en/US/products/ps7077/products_data_sheet0900aecd805bbe67.html) and 3924 (http://www.cisco.com/en/US/products/ps7077/prod_models_comparison.html).


However, a note found in documentation referencing an 8700W power supply for a 6500 series switch states, "Note: ~90% of PoE power is dissipated at the PoE device and along the cabling and not at the switch closet itself. Plan for cooling capacity for the switch closet accordingly". (http://www.cisco.com/en/US/products/hw/switches/ps708/products_data_sheet0900aecd8059a1ef.html)


If the note on the power supply is correct, then I believe that Cisco's posting of 3939 and/or 3924 BTU/hr is very misleading.


How should the maximum BTU/hr for a 3750E-48PD-F (or any other PoE switch) be figured? Using Cisco's listed maximum BTU/hr or by following the note that states approximately 90% of the power (heat) will be dissipated at the far end?

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mchin345 Wed, 10/31/2007 - 08:41
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The maximum power supplied by the Cisco Catalyst 3750-E PoE is 15.4W per port, total PoE power available on the Cisco Catalyst 3750-E with 48 PoE ports would depend on the installed power supply modules in the switch. With a 1150W power supply the 48-port switch can support up to 15.4W of power per port. The pairs 2 and 3 (pins 1, 2, 3, and 6) of the four pairs in Category 3 and 5 cables are used for both the Ethernet data signals and the DC power at the same time. The PD must accept either polarity of power from either pair set. This allows both crossover and straight cables to be used. Only straight cables should be used with the prestandard Cisco PDs.

dominic.caron Mon, 11/05/2007 - 10:38
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Look a the power output for the non POE switch.


907BTU/hr, 265W


To that, add 10 % of the POE your giving to end nodes.


Worst case is around 1200 BTU/hr.



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