3 Phase query

Tudor · 10 Sep 2018

Hi,

The short question is "Can I power a computer server, which has two power supplies, from different electrical phases"?

Long question/story.
I have numerous racks of servers & IT equipment in a Data Centre, each rack supplied with a single phase 32amp circuit. The majority of the IT equipment has two power supplies for resilience. New 32 amp circuits have been installed alongside the existing ones. I now need to switch the servers & equipment from the old to the new - preferably without switching the equipment off. Problem is, the new circuits are a different phase to the old circuits. Can I pull one of the power cords out of a server and plug it in to the new supply, so running on two different phases, and then move the second power cord over? This would keep the equipment up and running, but not sure if this will cause an electrical problem?

I'd appreciate your input/comments please.

Regards, Dan.

chivers67 · 10 Sep 2018

When I worked on Heating systems we always had to run all outlets on the same phase as form a maintenance perspective it may be dangerous as one could in theory have over 400 volts across the two phases.

I'm not certain with IT equipment though.

ban-all-sheds · 10 Sep 2018

I've never known IT equipment where you couldn't do that.

But in the race to the bottom someone could well have made something where it was risky - check with the maker(s).

I would have thought that running all the time on different phases would be preferable - makes data centre power maintenance easier.

But I would strongly advise not doing any power swap-overs while the servers are running. It may take longer, but can't they be emptied a few at a time and shut down?

Tudor · 10 Sep 2018

I took just over 1 year of discussions and planning to get our Data Centre powered down a few years back. Unfortunately, things tend to run 24/7/365. Swapping power cords with the kit running is the preferred option and has been done on some of our kit where the old and new phases were the same.
The kit is all from main manufacturers so I don't expect anything shoddy.
The 400 volts across phases was highlighted to me before, but not sure how this would actually happen, or is it a case of that the probability is that nothing will go wrong but there is still a slim chance.

seasickstevie · 10 Sep 2018

Assuming each individual item (box) has just one supply, then I can't imagine why there would be a problem. I mean no data is going to be at even a potential to the mains supply as such. Surely everything is fed by either the secondary from a step-down transformer power supply, or a solid-state psu. Find it difficult to see how a potential between two separate primary supplies would make a difference.

But then, I could be wrong!

mikeyd · 10 Sep 2018

Although I don't work in a data centre, I know of a couple of network switches with redundant PSU's powered from different phases by design. One of those is supplied from 2 different 11kV transformers. Not a problem. Sometimes (usually Bi-annual oil checks or something) maintenance involves isolating a transformer, so it's handy not to have to run a temporary extension from the nearest supply that we know is going to stay live. Even if we have to run a temporary cable from a completely different area to equipment which is normally fed from different phases off one transformer, I've never had a problem (this has involved generators in the past).

Edit:

Just seen your latest reply. In short, don't worry.

ban-all-sheds · 10 Sep 2018

Tudor said:
I took just over 1 year of discussions and planning to get our Data Centre powered down a few years back.

I can understand that, but I wasn't suggesting shutting the data centre down. And in fact if you have equipment with redundant PSUs on different phases that can reduce the need for shut-downs.

Unfortunately, things tend to run 24/7/365.

I'm sure they do, but I wasn't suggesting shutting any services down, just moving them so that individual physical servers can be powered down.

Swapping power cords with the kit running is the preferred option

Hmmmm.

ban-all-sheds · 10 Sep 2018

seasickstevie said:
Assuming each individual item (box) has just one supply

Tudor said:
server, which has two power supplies

mikeyd · 10 Sep 2018

Tudor said:
The 400 volts across phases was highlighted to me before, but not sure how this would actually happen, or is it a case of that the probability is that nothing will go wrong but there is still a slim chance.

We work with 3 phases all the time. It isn't a concern, any more than single phase is. It can still be just as nasty if you don't understand, and it's good that you shared your worry. All I can say, given your comments is that I don't think you should be worried about hot-swapping kettle leads just this once.

333rocky333 · 10 Sep 2018

I remember back in the 80's they made us put all computer sockets on same phase, but back then the data cables were like twin Arial cable with a metal screed, never see cat 5 cable then.

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3 Phase query

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