Missing One Stack Power Cable

[PolarPanda]

Hi,

        For a 4 stack Cisco 3850, would it be possible to not run the last stack power cable from 4th switch back to 1st one? We don't have a proper length of stack power cable, but able to run the rest of stack power cables between switches. Thank you.

[Joseph W. Doherty]

I would "guess" that's an "it depends" answer.

I'm unaware of all the power issues with 3850 power cables, but with the prior 3750 series, there were power limitations to how much power you could draw across cables.  You had to be careful between what each switch needed for power, and cable capabilities, in determining what size power supplies you needed and where they needed to be placed.

Unlike a chassis switch, which can often run the whole chassis on a single PS, and use the second for a backup, you could not do that with the 3750 series.  Again, for those, what are each switch's power needs, and what's can you draw through the power cables.

[Joseph W. Doherty · Accepted solution]

Don't know if the short power cables are long enough, but with data cables, one approach, to avoid the need for a long cable to connect top and bottom stack members has been to "interleave" the connections.

Assuming stack members sequentially numbered 1 to 4, top to bottom, you would connect 1 to 2 and 3, and 4 to 2 and 3.

[Kasun Bandara · Accepted solution]

@PolarPanda in this kind of cases, i think you can create two stack power groups. but i never tested in production. you need to make sure your power stack properly distributed across switches according to power budget. below links will help to get clear understanding

https://community.cisco.com/t5/networking-knowledge-base/how-to-form-a-catalyst-3850-data-stack-and-power-stack/ta-p/3156083

https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-9300-series-switches/white-paper-c11-741945.html.