Jay R. Ashworth
jra at baylink.com
Mon Mar 14 03:28:16 UTC 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.
Jay R. Ashworth jra at 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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