Discuss 3 Phase Power in Computer Data Center in the Commercial Electrical Advice area at ElectriciansForums.net



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Hi Everyone,

I'm new to this site, but have a rather urgent question. I work as an IT Architect and as such I have a responsibility for our Data Centers.

Our Data Center is fed by 3-phase power and it has come to my attention that our racks may be incorrectly wired. We feed two blocks of power into each of our server racks to provide resiliant power to the servers. However it seems that the power blocks are on different phases within a single rack i.e. Rack 1 has power feeds from L1 and L2, Rack 2 L2 & L3 etc...

The question is, is this safe, bad practice or even legal?

I have taken advice from two electricians, one said that ideally we should have each row of server racks on one phase each, but the best we could do it at least put only one phase in each rack and place a Yellow Danger 415v sticker on the from, with details of how the connections are made and do not connect to adjacent rack.

However the other electrician, said that we only had to put the Yellow stickers ion each rack and do nothing more.

Obviously one solution costs £1000's and the other around £50 in stickers.

Can someone please advise what is the correct thing to do, obviously I do not wish to be putting people's health at risk.

Many thanks in advance.

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  • Thread Starter Thread Starter
  • #2
For my money, I'd go with sparkie two.
Its not unsafe or bad practice to have two phases in the same rack as long as there are adequate warning labels.spend£100 and go overboard
the original installation could have been put in this way to share the loading over the phases, or to ensure you did not lose all the equipment should one phase fail.
i wouldn't mind betting that you have at least one duplicate piece of equipment on seperate phases.belt and braces,:)


  • Thread Starter Thread Starter
  • #4
I personally would place each rack on a single phase, this way there is less chance of having 400/415VAC across expensive peices of equipment; if a fault does occur.

Just ensure that the load on each phase is balanced and your away. Athough the cheaper option is easier, you should do a cost-benefit analysis on what would happen if one of the racks did go bang? Would a new rack cost more than it would cost for the powr supplies to be changed?


No problem with just putting warning labels on stating that 400v is present within the rack but are your servers backed up by UPS's in case of a mains failure with a back up generator being a data centre? Last thing you want is to lose power and data at the same time.
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TOM dont scare the man:eek:, if it was installed correctly it wont go bang.230v will do as much damage to computer equipment if it all went wrong.


  • Thread Starter Thread Starter
  • #8

If the server racks are housed within the same cab which no doubt will be earthed, then it is highly unlikely that 2 phases would short to earth at once giving you a PD of 415V anyway.

Label it up very clearly and all is well.;)


  • Thread Starter Thread Starter
  • #10
Resillient power from two different phases... sounds cock-eyed to me.

Data centres I've worked on that provide two supplies to data-cabs (most all of them) usually do it through a PDU (Power Distribution Unit) with supplies coming in to the PDU from different matched sources, not different phases of the same source. The PDU senses Source 1 (eg, mains fed from 11k Ring 1) fail and switches to Source 2 (eg, mains fed from 11k Ring 2, UPS/DRUPS.)

Is there a PDU in this case?

Each radial from the PDU DB is then protected by it's MCB. No RCD or RCBO due to leakage issues.

If you really are using the same source for both supplies spend £50 on stickers, if yr not, ignore most everything of what I jut wrote.
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