[ale] Considerations Regarding Dual Power Supplies

[Jeff Lightner]

I wasn't saying he should worry about it but simply that I'd seen a
presentation once that talked a lot about grounding.  It talked some
about how people would run one long ground to one location then a short
ground to someplace else and be surprised when a short occurred that
caused all the power to suddenly go through that short ground and
essentially cause it to become a live circuit.  The presenter talked
about things such as shunts etc... that allow you to connect ground
sources so that the shortest path is still to ground to prevent this.

Having seen a whole data center go off line with cascade failures from
one panel to another until all of them were fried I know that power
considerations aren't trivial.  I certainly wouldn't present myself as
an expert on power because I'm not.  I was just trying to answer the
idea of grounding and redundancy in the OP's post.   When I deal with
multiple PDUs I seldom ask myself "where is the ground for this" as I'm
relying on the electrical folks that create the circuits I'm plugging
the PDUs into to have done their job properly.

-----Original Message-----
From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of Greg
Freemyer
Sent: Monday, October 06, 2008 4:13 PM
To: ale at ale.org
Subject: Re: [ale] Considerations Regarding Dual Power Supplies

Jeff,

I don't know why ground loops are not typically a big issue with
servers and dual power supplies, but I have RARELY seen anyone worry
about it.

The exception is, I have seen a 30 foot shaft sunk into the ground
near a computer room and a ground line from that directly connected to
a ground distribution panel, which in turn was connected out to the
servers.

Greg

On Mon, Oct 6, 2008 at 3:33 PM,  <hbbs at comcast.net> wrote:
> In audio-land, you have to be mindful of not creating ground loops,
i.e, a closed circuit of what should be ground in which EMI (especially
60Hz hum and harmonics) can be induced.
>
> Knowing that, does it cause problems to run power cables from a
machine with two power supplies to two different PDUs in a server rack?
Or, is it preferable to connect the two power cables to as close to the
same point as possible (i.e., two electrically adjacent outlets in the
same PDU)?  Aren't the ground pins in each of the two power supplies
going to be connected together inside the machine?  If so, it seems as
though having the two grounds form a big loop might bring a lot of hash
into the machine through the ground lines.
>
> - Jeff
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://mail.ale.org/mailman/listinfo/ale
>



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