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Topic Title: In cabinet 3 phase
Topic Summary: DO's and DONT's for Server PSU
Created On: 20 May 2012 10:30 AM
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 20 May 2012 10:30 AM
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deleted_1_Syrina

Posts: 1
Joined: 20 May 2012

Hopefully someone can point me in the direction of regulations about this:
We've installed many servers across the UK and a lot of the server racks are fed by 3 Phase power. This is presented in a PDU unit, where C13 to C14 cables are run to each server. Question, some engineers do not check that on a dual PSU server, there is a possibility that a 220V from differing phases can be connected introducing 400V into an enclosure rated at 220V. I can't believe this is acceptable, and ask if anyone knows of regulations highlighting this.

Kind regards

Ian
 20 May 2012 11:13 AM
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Dave69

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Joined: 16 July 2011

why is the enclosure only rated at 220V? Single phase can be over 240V in some cases
 20 May 2012 01:34 PM
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gkenyon

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Originally posted by: Syrina

Hopefully someone can point me in the direction of regulations about this:

We've installed many servers across the UK and a lot of the server racks are fed by 3 Phase power. This is presented in a PDU unit, where C13 to C14 cables are run to each server. Question, some engineers do not check that on a dual PSU server, there is a possibility that a 220V from differing phases can be connected introducing 400V into an enclosure rated at 220V. I can't believe this is acceptable, and ask if anyone knows of regulations highlighting this.



Kind regards



Ian
Ian,

Please could you explain why you think this is a problem?

Each PSU is getting only single-phase power. Typically, PSUs in Servers, etc, are independent, single-phase, enclosed devices, and their rating is not being compromised by the power supply arrangement. Before a technician comes into contact with "three-phase" (i.e. "phase to phase") power, there would need to be more than one "enclosure" damaged or removed, and this would, in a work environment in the UK, potentially constitute a breach of legislation.




Also, what are you terming an "Enclosure"? From the Wiring System perspective (IEC60664-series, or BS7671 in the UK), the Enclosure is the PDU (if the PDU is "hard-wired"), or in the case that the PDUs are fed from underfloor/above cabinet busbar-type of industrial-type ("Commando") socket outlets, the "Enclosure" of the Wiring System stops at those socket outlets, and each PDU feed is then a separate "connected appliance".

BS7671 (and IEC60664-series) cannot proscribe three-phase power in the same "enclosure", as this is necessary in the wiring system itself.

There are recommendations in BS7671 for labelling of enclosures which contain unexpected voltages, and provided this is complied with, then there should be no problem.


Even if you insist on both supplies being the same phase (even if not from the same final circuit DB), if each supply is fed from a UPS, what happens when the normal supply goes off? The two UPS's are highly unlikely to be "phase-locked" and "frequency-locked", so in theory, the phase difference between the two supplies could well be cycling between 0 and 180 degrees - i.e. you would have in Europe upto 460 V nominal (i.e. up to 506 V) between the phase conductors of each supply to your Server !

Does this cause a real problem, that competent IT technicians should not already be aware of?

-------------------------
Eur Ing Graham Kenyon CEng MIET TechIOSH
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