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power requirement for single rack

Posted on 2016-07-16
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Last Modified: 2016-08-02
Hello experts,

I want to put a single rack 42 U in a room with 5 Switches, each switch has dual power supply adapters and they are POE+ with 1100 watts.

Just wandering how to calculate the power consumption on this rack and what will be required to keep it running 24x7?

A detail explanation will be great as I will add more racks with time.

Thanks,
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Question by:Zak
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Dr. Klahn earned 500 total points
ID: 41715023
Per the description above:

  • each rack contains 5 switches
  • each switch contains two power supplies
  • each power supply is 1100 watts

5 x 2 x 1100 = 11,000 = 11 kW

Figure a 10% extra power pull at startup if each unit is powered on individually in sequence (12.1 kW).  If the rack is US 120V, you'll need 100A service and socket.  The maximum power pull occurs only at startup, so this configuration rack will require 37,000 BTU of cooling.

Figure a 50% overhead extra power pull at startup if all units are powered on simultaneously (16.5 kW).  For US 120V, you'll need 150A service and socket.  The maximum power pull occurs only at startup, so this configuration rack also requires 37,000 BTU of cooling.

These are the maximum draw figures and imo you should design to these, not to what the racks normally draw.
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by:nobus
ID: 41715026
you can measure the total current drawn, with a current clamp meter like fluke offers
http://en-us.fluke.com/products/clamp-meters/

then you have an idea of the current and power needed
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by:nobus
ID: 41715702
but all these  calculations give only an estimate - while measuring gives the actual consumption
up to you to decide which way you go
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by:Zak
ID: 41715827
nothing is placed now I just want to know before putting rack.
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by:nobus
ID: 41715894
then you can't possibly measure anything
contact an electrician, they should know
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by:Danny Child
ID: 41716061
I think the calc above is wrong, in terms of factoring each PSU at its full rating of 1100W.

The switches are factored that they 'could' run on a single PSU if needed, and there will be a safety margin on them already.  

So, I would say that you work on 5 x 1100 W = 5500 W = 5.5 kW

The calc tools above in Shaik's post are good, but they are fairly manufacturer specific, and don't seem to list standard Cisco kit, for instance.  If you post the models of the actual switches themselves, then we can check the manufacturer's recommendations.
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by:Dr. Klahn
ID: 41716063
I concur if the power supplies configured with one as redundant backup.  Unfortunately the problem statement didn't say whether both supplies are active or whether one is backup.
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by:Zak
ID: 41719798
Is there a power consumption tool from Cisco? I am looking for Cisco readings.
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