Re: AlphaServer hardware question
From: Mike Naime (mnaime_at_kc.rr.com)
Date: 06/27/04
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Date: Sun, 27 Jun 2004 02:24:04 GMT
Nic Clews <sendspamhere@[127.0.0.1]> wrote in message
news:cbgqkk$4sa$1@lore.csc.com...
> TANSTAAFL wrote:
> >
> > I have a fully loaded AlphaServer 2100A RM. The documentation says
> > only one power supply is need to support a fully configured server.
> > This one has a second one for n+1 redundancy.
> >
> > Each power supply handles 120V with a maximum current of 10A. Both
> > power supplies will be supported by the same circuit. If the
> > consumption would not exceed one the capability of one power supply, I
> > do not need a 20A circuit right?
>
> Arguably you are correct.
>
> The power supplies are switching, so basically, if one supply draws 10A,
> then two will share the load and draw just 5A each. There is some small
> overhead of course because it is not 100% efficient.
>
> HOWEVER, lets talk electrics. NEVER NEVER expect to constantly draw the
> rated current load from wiring. This is the way to electrical fires. The
> supply should have at least *double* the expected maximum total current
> draw for the circuit, ideally 2.5 times. In the UK this is backed up
> with a ring type circuit for multiple connections.
>
> In your case, I would have a 32A breaker, and wiring cable of carrying
> 40A plus, the breaker must ALWAYS act lower than the total capacity of
> the wiring.
>
> So in your case, lets say your system develops an electrical fault, and
> tries to draw 20A. What would happen? Would a breaker or fuse trip at
> less than 20A? Or would the wiring go into meltdown and overheat?
>
> That is what you need to be concerned with.
>
Plus you need to consider the power-on surge current. Your normal load may
be 10A. But your power-on surge may be 20A. And you system may not start
up correctly if it cannot draw all of that power when you turn it on.
> --
> Regards, Nic Clews a.k.a. Mr. CP Charges, CSC Computer Sciences
> nclews at csc dot com
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