Connecting a 3750X power stack

[Kevin Dorrell]

I am having some difficulty figuring out the power stack cables for 3750X.

We recently had somone (physically) re-install a pair of 3750X switches, and after they had finished one of the switches was complaining of insufficient power budget.  Each switch has two 350W power supplies, and I have not had any problems with this before.  The installers seem somehow to have connected the two top sockets together and the two bottom sockets together.

So I looked at http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst3750x_3560x/hardware/quick/guide/3750xgsg.html#wp70634, but I found the document very confusing.

I understand that the bottom socket of one chassis should be connected to the top socket of the next chassis, and so on as a daisy-chain, until the last one, which should be looped back to the first in the chain.  I also understand that the maximum number of boxes I am allowed to daisy-chain in this way is four.

But does it matter which way round each cable goes? In the diagram, it seems to show the green end always in a top socket, and a yellow end always in the bottom socket.  But in another installation, we seem to have the correct cross-coupled loop, but the yellow end always in a top socket and the green in a bottom socket.  Yet another installation has one chassis with both green ends and the other chassis with both yellow ends.  Does this mean the cables are reversible?  The XPS2200 installation guide seems to suggest they are not.

Kevin Dorrell

Luxembourg

[Reza Sharifi]

Hi Kevin,

I have done a few stacks of 3750X switches and have never had any issue using the green or yellow.  As matter of fact, I have never paid attention to the color.  I just plug them in. Also, I just plug in the top socket to the top socket and the bottom socket to bottom socket and have not seen any issues.

HTH

[Kevin Dorrell]

Hi Reza,

That is interesting, and not what I was expecting.  I wonder what was going on in my case then?  It's a pity I didn't take a photo at the time, and I don't have the message in my syslog archive because the switch was off line at the time.  I do remember though that when I did a "show stack-power detail", the power budget for each of the two switches seemed to be different, which is strange because they are identical switches.  After I had re-connected with the cables, they were the same once more.

I guess it will remain a mystery until I next get to try it in the lab.

Thanks once again for answering.

Kevin Dorrell

Luxembourg