PDU for Single C7000 w/16 servers when wall socket is single-phase/16A only

[chuckk281]

Ulf had a power question:

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I am trying to find the right PDU for a C7000 enclosure w 16 blades and 6 PSU’s, so need two PDU’s, but customer facility power is 16A/230 single-phase. I can’t find any 16A rated PDU with >3 C19 server-side inputs? Any tips?

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Feedback:

From Sunya:

   I’m sure totally current drawn by 16 blades at 100% utilisation is more than 16A.  You can’t provide them only 2 of 16A PDUs. That’s mean if one sources is outtage.  Your another PDU will be melt or  its circuit breaker is tripped.

     In case of your customer can provide only 16A rating of circuits breakers.   I suggest you propose with  4 of  16A core only corded  PDU.   Along with  a pair (AF500A) of extension bar.

Input from Dan:

I would change the design slightly in that you want to mirror left and right as best you can, and with Dynamic Power mode on, I would make sure that PSU 1 and 2 are coming from different circuits. Same with PSU 4 and 5.

This is assuming N+N redundancy mode.

My point about Dynamic Power is you will have a higher load on some PSUs and no load on others.  So you want to make sure you aren’t putting the highly loaded connections on the same circuit.  N+N or N+1 modes could change which supplies should be cabled where, so just pay attention to the Power Subsystem page in the OA as it will show you which supplies are sleeping and which are being used.

If they really only have a single 16a circuit for the entire enclosure, you might not get all 16 blades up and running.

I would certainly recommend you enable at least a Static Power Limit on the Power Management screen towards the bottom.  That way when you hit the cap the enclosure will prevent additional blades from coming online that might trip your breaker.

And input from Monty:

The reason the c7000 installation guide recommends connecting power supplies 1-3 to one AC feed and supplies 4-6 to the other feed, is that we have both OA hardware and firmware that assume those bays to be on the same AC input circuit.

In c-Class, all the power supplies that are active are all sharing the entire load.  The purpose of the Dynamic Power savings feature on the OA is to increase the power supply efficiency at lower loads by placing one power supply on each “side” in standby, to increase the utilization of the remaining supplies near 50%.  If the customer has scrambled the AC input feeds on each side, then they are exposed to enclosure brownout if one AC input circuit is lost.

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Other comments or questions?