is there such a setup as primary power source?

[Anna Cheng]

I will have a few coming in and am planning the setup. From what I looked at, I should configure the power supply as N+N, with power 1, 2, 3 connected to power source A, and with power 4,5,6 connected to power source B.

But as we plan to install 3 C7000 enclosures per rack, and I plan to give our cabling team a consistent setup, i.e. all left hand side power supplies go to power source A, all right hand side power supplies go to power source B.

Will it mean that there will be more power drawn from power source A as I assume it is the primary ? or have I been confused?

Obviously, I have to make sure both power towers are able to support full load but I am curious as to how it works.

thanks
anna

[Adrian Clint · Accepted solution]

The power supplies are rated at 2250Watt.

With N+N it turns on the power supplies in pairs. When the existing power supplies are more than 50% used it turns on another pair.

So upto a total use of 2250watt power supplies 1 & 4 are turned on.

Between 2250w and 4500w power supplies 1,2,4,5 are turned on.

Over 4500w all power supplies are turned on.

So N+N does balance between A and B feeds if 1,2,3 are on A and 4,5,6 are on B.

[Adrian Clint]

Forgot to add.... what PDUs are you going to put in the racks for 3 enclosures?

[Anna Cheng]

Aldrian,

thanks.
I am checking with facility to find out the PDUs, but why does it matter?

Given that the power supplies are paired as 1/4, 2/5, 3/6, does it mean that PS 1 and PS 4, cannot fail at the same time? I guess they can as doc stated any 1 through N, but just want to sleep better.

[Adrian Clint]

PDUs?: Well you want to balance power load. So are you using 6 single phase HP PDUs for the 3 enclosures or 3-phase PDUs or are you using 3rd party with many outlets. You want to make sure that you are balancing the load across all three phases if possible.

As for if one of a pair fails.... the next pair turn on in N+N mode.
So if 1 or 4 fails and you have 1,2,4,5 on then 3 & 6 would turn on.

In N+1 the next PSU would turn on.
I think for N+1 the sequence is
1,4,2,5,3,6 - its in the manual.

[Anna Cheng]

Thank you.
I believe we use 3-phase, but will have to check.

anna