Surge suppressors

Robert G. Brown rgb at
Fri Nov 1 08:36:12 PST 2002

On Thu, 31 Oct 2002, David Mathog wrote:

> I plugged 5 single CPU Tyan 2466 machines into a single
> TrippLite 6 Isobar Ultra.  Circuit was 20A breaker, 20A wiring,
> 15A plug. The 5 nodes didn't blow the 12A fuse in the

I'm not sure what this means.  15A "plug"?  Either this is horribly
dangerous and a code violation or irrelevant -- if you use a 20A
breaker, everything in your circuit downstream had better be rated for
20A or be fused for lower current operation so you can't start a fire
and not blow the (or a) breaker first.

See for example

for a picture of what can happen if code is not adhered to.  Although
for an electrical motor, it is still apropos since motors often ALSO
have poor power factors.

Being the personally paranoid, I don't think 15A receptacles should even
exist in a universe with 20A circuits mixed quite freely with 15A
circuits, as they are in most houses.  Even a dedicated wiring inspector
may not get down on his knees to read the rating of every receptacle in
a circuit, and even a very good contractor can have an employee who
grabs something from the wrong box (of there are wrong boxes to grab).
It is quite harmless to use a 20A rated receptacle in a 15A circuit, but
the other way around is very dangerous, and the cost differential is
literally pennies.

> surge suppressor.  It ran ok for an hour  with "openssl speed"
> running in a loop on all nodes. These suppressors may have
> too small a breaker if we add second CPUs to each node but

I think that they might.  Those CPUs use a lot of power, and the
switching supplies, if not PFC, appear to have a PF of around 0.8 (so
you draw a peak current about 1.25 higher than what you might expect
based on average power.  We couldn't get 10 nodes on a 20 A circuit
here -- had to settle for 8.  Which means that with 5 you'll be right on
the same margin, where YMMV depending on how sensitive the protector is
to peak vs average current and how much other stuff you have in the
nodes that draws current.

I'll be very interested in seeing whether they survive or don't.


Robert G. Brown	             
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at

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