[Server-devel] School networks and electrical equipment damage

Fri Jun 7 10:02:02 EDT 2013

This and the other posts in this thread have great data points and anecdotal evidence.  It would be nice to have it synthesized into a wiki page.

From: Kevin Gordon 
Sent: Friday, June 07, 2013 8:39 AM
To: John Watlington 
Cc: XS Devel ; OLPC Devel 
Subject: Re: [Server-devel] School networks and electrical equipment damage

More data:

In general, we have placed the UPS for the phone line protection directly between the biccs block (or phone company termination point) and the first jack on the line, which is usually the split jack for voice/dsl. From the split jack, the DSL line goes into a second  UPS which powers the DSL modem and the first AP.

Certainly the UPS should be grounded. However, to be trite, I have seen cases in the wild where power is being saved, and sometimes the UPS is turned off, and/or unplugged. So, it might be important to evaluate whether the surge suppression still works when the UPS are unplugged from mains, and/or if they have fried first.  Also, we have found that the surge suppression has a fixed number of faults before it is no longer effective.  seems to depend on the make/model/quality and the alignment of the planets.  In the case of the APC RS 1500 series, a stress test showed that spiking  to just double voltage, which did not fry the UPS machine, there was no protection left after 5 such jolts.  Therefore, it is also important to monitor the UPS  logs regularly to see what is going on.

As of yet and as far as I know, <knocking on head>  we have never been hit by lightning,but we have lost UPS do to surging, usually on unplanned power outages.  Again, so far, we have never lost an AP or a modem.

Last night I ran 100 speedtest.net scripts 50 with the phone line plugged into the UPS and alternated every-other with 50 not plugged in, on a 5Mb synchronous DSL.  There was no significant difference, and in fact the average score was a teeny tiny tad higher on the protected tests, for all of Ping, Download, and Upload.  

So, as usual, your mileage may vary, but this has been our experience.

Cheers,
KG

PS: in raw cost, a good UPS is more expensive to replace than an AP or switch.  However, you don't lose your configuration, and sometimes it takes days to get a DSL modem replaced from the telco.  Sometimes it makes sense to put the more expensive UPS in the way of even cheap infrastructure.

On Fri, Jun 7, 2013 at 12:44 AM, John Watlington <wad at laptop.org> wrote:

  I considered sources such as James' theory, as well as someone
  connecting one of the ethernet cables to line voltage, and neither
  accounted for the level of damage you described.

  But I can't agree more with James' point about building from the ground
  up.   The first thing we used to wire up in a computer room was the
  frame grounds --- with modern SOHO gear that all comes through
  the grounded power plug.   But it has to be plugged in to be grounded
  (i.e. protected).

  Coincidentally, today I checked out the earth ground in the new hardware office
  and wired up the workbench grounding in OLPC Boston's new digs in Davis Sq.

  wad

  On Jun 6, 2013, at 6:51 PM, James Cameron wrote:

  > On Thu, Jun 06, 2013 at 01:58:58PM -0600, Daniel Drake wrote:
  >> And the most surprising thing - we had not even turned on the network
  >> yet, pending some electrical work. Everything was connected up except
  >> one crucial link - the UPS was not plugged into mains power. So all of
  >> this damage happened without any of the devices having a connection to
  >> the mains.
  >
  > Actually not plugged in?  The whole network was therefore either
  > isolated from building electrical earth ("ground") or had a series of
  > surreptitious connections, the critical one being the telephone line.
  >
  > Hmm.  Lightning wasn't necessary.
  >
  > Here's my theory:
  >
  > Each long run of ethernet twisted pair becomes one side of a capacitor,
  > the other side being the building wiring, piping, or structure.
  >
  > The long run of telephone wire picks up static charge from wind,
  > lightning ground currents, test currents from the telephone exchange
  > or line workers, or induced currents from other subscribers or power
  > network switching.  Even turning on many lights.
  >
  > http://www.pololu.com/docs/0J16/all can give you an idea of what can
  > happen.  Any of these events will induce a starting pulse of DC in the
  > telephone wire, which is analogous to the length of DC power cable in
  > the Pololu explanation; the inductor.  The low equivalent series
  > resistance (ESR) capacitor can be thought of as the long cabling
  > against the building.
  >
  > As a result of the capacitor and the inductor, the voltage is
  > amplified until it reaches the breakdown voltage of whatever is
  > connected.
  >
  > Having the UPS plugged in might have prevented this voltage from
  > finding a route through something more precious.  Instead, it might
  > have found a route through a series of surge protection devices in the
  > UPS, and then the only damaged equipment would be the ADSL modem.
  >
  > The convention is to build from the ground up.  Don't plug the cables
  > in until the ground is available, and then plug them in in strict
  > order.  People get away with not doing this because the damaging pulse
  > isn't constant.
  >
  > (Reminds me of the time that I pulled a UPS input power plug out
  > instead of just turning it off.  A bad idea.  The last pin to separate
  > was active.  The connected equipment lost ground reference, the only
  > ground reference that remained was through a device, so it took a full
  > hit and died.  The resulting current passed into the building ground,
  > and triggered the earth leakage breaker on the circuit that the UPS
  > was originally connected to.  Other equipment connected to that
  > circuit powered down.)
  >
  > (Reminds me also of working for a cable contractor in the 1980s,
  > looking after their cable management system on a VAX ... they were
  > putting millions of cables into a power station, and the build was
  > done from the ground up; that is cables were tracked as to whether
  > they had been terminated yet, and the list of unterminated cables was
  > a special report from the database that they always wanted to see.)
  >
  >> I have seen that some UPSs (unfortunately not these ones) allow a
  >> phone line to be passed through them, supposedly offering some
  >> protection. Would such a system protect against a lightening bolt,
  >> assuming thats what happened here?
  >
  > Yes, but only if the UPS was earthed.  It would also protect the ADSL
  > modem.  It would also protect from most other causes of a current
  > pulse arriving on the phone line.
  >
  > --
  > James Cameron
  > http://quozl.linux.org.au/
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