How to verify sufficient PoE power provided to all PoE devices connected to switch??

[tommls]

We have a SF300-24P 24-Port 10/100 PoE Managed Switch, which we've used for years, no problems.

Also a SF300-48P 48-Port 10/100 PoE Managed Switch.

They have various computers and IP phones attached to them.

The IP phones are all PoE devices.

Plus we recently installed two SonicPoint ACe access points which use PoE.

SonicWall says the ACe devices must be connected to a PoE switch that can provide up to 25 watts PoE power to each ACe, we have two ACe devices, so we need the switches to provide at least 50 watts PoE power, plus however much PoE power for the IP phones.

How do I determine how much PoE power these switches can provide and how much PoE power these switches are currently providing??

The spec sheets I found don't help me very much.

Looking at the PoE properties for the 24-port switch, I see:

Nominal Power:
180 W
Consumed Power:
48 W
Available Power:
132 W

For the 48-port switch, I see:

Nominal Power:
375 W
Consumed Power:
72 W
Available Power:
303 W

Does this mean the switches are providing the desired quantity of power for the phones and SonicPoints??

Thank you, Tom

[boayers · Accepted solution]

Hey there,

My name is Patrick with Cisco eSupport. It is important to know that there are 2 standard for power over ethernet. There is the standard PoE (802.11af) which your SF300-xxP switches have and the newer PoE+ (802.11at). Standard PoE can supply 15.4W of power over each cable, while PoE+ supports up to 30W. 

You can read more about the detailed specification of our switches here:

http://www.cisco.com/c/en/us/products/collateral/switches/small-business-smart-switches/data_sheet_c78-610061.html

In order for your ACe devices to get the required power you would need either a 300-xxPP series switch or an appropriate 802.11at compliant PoE injector for each of the access points requiring the 30W. Hope this helpful. Let me know if you have further questions.

Best,

-Patrick

[tommls]

The numbers I got from the PoE settings page suggest the PoE budgets for the switches are nowhere near being fully used.

Does this mean that a connection could use more than 15.4 W on a given cable so long as the total PoE budget is not being used up??

Thank you, Tom

[boayers]

I believe the port will not allow you to exceed the maximum limit of 15.4W per cable. The device may light up, but will not function properly if it requires a PoE+ source. The total PoE budget only needs to be considered if you have many PoE devices on multiple ports of the switch.

-Patrick

[tommls]

The SonicPoint(s) functions...most of the time.

Sometimes one of them loses connection and the only remedy we know of so far is to unplug and replug its cable in the patch panel.

We are trying to figure out why they lose connection.

We are investigating everything we can think of.

We do have many PoE phones in the building connected to multiple switch ports. All the phones function properly, correctly, and do not lose their connection.

I'm not convinced replacing the switch is the proper solution.

Thank you, Tom

[boayers]

If the access points require more than 15W of power then they will not be guaranteed to operate correctly. It is a possibility that the lost connection is due to an intermittent power problem. I wouldn't expect there to be any issue with the phone because they do not require the higher wattage. I would highly suggest connecting the device through a PoE+ injector to see if the problem goes away before replacing a switch. 

-Patrick