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From: David Lesher <wb8foz () nrk com>
Date: Sun, 13 Mar 2005 18:12:46 -0500 (EST)
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. Line power is a sine wave. The cheapest inverters make square waves {because it's how an inverter works; one transistor comes on, making a positive-going waveform; the second one takes its turn, making a negative-going one. Back and forth.} But the transitions are quite abrupt. Better UPS's use a stepped squarewave, maybe 3 levels, instead of one. The be$t make sine waves... [Side note: the usual switcher supply on a PC/Sun/etc does not give a damn re: sine vs square wave; as the first thing it does is make DC out of the AC and filter 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. But then, so do big power hits. If you ever shake a strip and hear it rattle, the MOV's were #1 on the Smoke God's list. And in the WORST cases, the heat melts the plastic strip/sets it on fire. 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. -- A host is a host from coast to coast.................wb8foz () nrk com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433
Current thread:
- Fire Code/UFC Regs? Michael Loftis (Mar 11)
- Re: Fire Code/UFC Regs? David Lesher (Mar 11)
- Re: Fire Code/UFC Regs? Josh Vince (Mar 13)
- Re: Fire Code/UFC Regs? Joe Maimon (Mar 13)
- Re: Fire Code/UFC Regs? Mark Radabaugh (Mar 13)
- Re: Fire Code/UFC Regs? Dan Hollis (Mar 14)
- Re: Fire Code/UFC Regs? Douglas Otis (Mar 15)
- Re: Fire Code/UFC Regs? Joe Maimon (Mar 13)
- nanog David Lesher (Mar 13)
- Message not available
- Re: nanog Jay R. Ashworth (Mar 13)
- Re: nanog Michael Loftis (Mar 13)
- Message not available
- Re: nanog Jay R. Ashworth (Mar 14)
- Re: nanog [really inspectors & MOV's] David Lesher (Mar 13)