C3850 715w vs C3850 1100w

[matthew.norman]

Hello all,

The title explains most of it.

There's two 48poe+ models of the C3850. One has 715w of power and the other 1100w. What would be the deciding factor between these?

To me the 715w model would be sufficient as it provides 435w of PoE which would be enough to power basic IP phones on every port.

Should the power also be considered when you stack x number of switches?

Regards

Matt

[Reza Sharifi]

Hi,

Usually 715w is enough to power up all Cisco phones. Sometimes other devices made by 3rd party vendors can consume more power than the phones (e.g cameras, card readers, etc..) and that is why there is also 1100w power supply. As for stack, even though you can stack the power using the stacking power cable I would still use the same PSU on all switches.

HTH

[matthew.norman]

Hi Reza,

That helps. So I guess it just depends on the poe requirements.

I've seen a demo of stack power where a single PSU held up the entire stack of three. This is a very unlikely scenario I guess but would a single 715w PSU be capable of this?

Also when there are PSU failures and stock power kicks in, could it possibly take away some of the poe power that is normally available?

Appreciate your help.

Matt

[Reza Sharifi · Accepted solution]

Hi Matt,

Even if one 750w can hold up the entire stack, I would not suggest such a design.  There is just too much risk involved in case something goes wrong with the power, IOS, etc..

As for your second question, as long as there is enough wattage to support all POE devices it should work fine, but if your devices are critical, I would even put a redundant power supplies in each device just in case.

HTH

[matthew.norman]

Thanks again Reza,

I wasn't implying that I intend to use a single power supply for the entire stack.

I was talking about the very unlikely scenario that multiple power supplies fail within the stack.

Regards

Matt

[Joseph W. Doherty]

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Posting

No, not real common, but a branch circuit dropping can take down multiple power supplies.

BTW, don't know if it applies to 3850 stacks, but with 3750 stacks, they had a wattage limit on the power cables.

[Leo Laohoo]

I'm with Reza here. 

If using only 750w PS, then I'd get a second 750w PS (per unit) for redundancy purposes.  

Also, as to the debate of using 750w PS vs 1100w PS will depend entirely on how much allowance is left as there are some devices nowadays that require a minimum of 20.0w PoE.  

There are some IP Tel that will require uPoE and some wireless access points that require 26.0w PoE.