7945 - PoE Class 3

Unanswered Question

Hello,

We are designing a 520 Ip Phones UCC solution for a client, the LAN Switches we are proposing are 3750G-48PS and the 520 IP Phones we are proposing are 7945G.

On the 7945G Product Overview page:

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps379/ps8534/product_data_sheet0900aecd8069bb80.html

we see that the phone Power supports IEEE 802.3af PoE (Class 3).

and for the 3750G-48PS POE Switch:

http://www.cisco.com/en/US/products/hw/switches/ps5023/prod_models_comparison.html

we see under the 'PoE Class 2/PoE Class 3 Devices Supported' column that only 24 PoE Class 3 devices are supported.

Does that mean that the 7945G being PoE Class 3, the 48 port PoE LAN Switch will only support 24 7945 phones?

And, if yes, is there a way to 'tweak' the LAN Switch Power settings, or feed in more power to the LAN switch, to make it support all 48 ports for Class 3 PoE devices.

Thanks & Regards,

Kartik Bhatia

I have this problem too.
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Paolo Bevilacqua Wed, 10/07/2009 - 03:53

Correct, you could use the 7942 that are poe class 2, or 2x 2960PS 24 ports instead of the 3750.

rob.huffman Wed, 10/07/2009 - 04:44

Hi Kartik,

It's excellent that you picked up on this before moving ahead :) Just to add a note to the great tips from my good friend Paolo (+5 ponts here buddy!)

WS-C3750E-48PD1150W = 48x 7945/7965

WS-C3750G-48PS = 30x 7945/7965

When making these decisions, this is a very valuable tool;

PoE calculator

Use http://tools.cisco.com/cpc/launch.jsp

Cheers!

Rob

rob.huffman Wed, 10/07/2009 - 05:20

Hi Kartik,

The bottom line here is that the 7945 is not a "true" Class 3 device in that it actually uses 12w vs 15.4w for Class 3 devices.

If you are looking at putting in 48 (7945) phones you can either uses 2x24 port 2960's as paolo nicely noted or 1x WS-C3750E-48PD1150W = 48x 7945/7965

Hope this helps!

Rob

rob.huffman Wed, 10/07/2009 - 06:09

Hi Kartik,

No worries :)

1. From the doc you linked;

Cisco Catalyst 2960-24PC-L can support 24 simultaneous full-powered PoE port at 15.4W.

2. Sorry my friend, no "magic" tweaks.

Cheers!

Rob

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