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Re: nanog

  • From: Jay R. Ashworth
  • Date: Sun Mar 13 22:29:26 2005

On Sun, Mar 13, 2005 at 06:12:46PM -0500, David Lesher wrote:
> Speaking on Deep Background, the Press Secretary whispered:
> > Perhaps someone who knows EE can enlighten me?
> 
> I'll try.
> 
> The #1) is BS. #2) is true.
> 
> If ANYTHING is, it's square waves. [Huh?]
> 
> Virtually all surge protectors have MOV - Metal Oxide Varisters -
> within. These are devices with s sharp knee on their Voltage vs
> Resistance curve. In other words, they do not conduct for a 120V
> level, but do at 200, shunting that overvoltage to ground.

Careful: that conduction voltage is peak, is it not?

120VAC is RMS; the peack voltage is, like, 175, isn't it?

> Now, via magic called Fourier, sharp transitions mean lots of short,
> high voltage pieces-parts. [trust me, or read up..you can create
> any square wave from an infinite series of sine waves..]
> 
> So the ""risk"" I hear talk about is this. The MOV's in a strip
> conduct slightly on those squarewavish USP output waveforms. This
> results in 2 things, gradual loss of MOV efficacy, as they
> degrade slowly with use; and the worry that iffen the MOV's
> absorb too much squarewave crap, they'll explode. See, MOV's
> turn transients into heat. Line transients are assumed to be err
> transient & tolerable. Continuous stuff is another issue...that
> can overheat the MOV and cause it to worship the Smoke God.

Smoke emitting diodes?

> So let's ban surge strips on UPS's...But wait... lots of machines
> have MOV's inside their power supplies.. Shhh!!!

:-)

> But note that the OP does not have a MOV issue; he has an inspector
> issue. His best answer there may be buying outlet strips that
> offer no surge protection. He likely will need to first pin
> the inspector down on what rules he's allegely broken, however.

This is the most cogent point to date, and the one I made off list: ask
him to quote chapter and verse.

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra@baylink.com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

      If you can read this... thank a system adminstrator.  Or two.  --me




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