# nanog

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
offer no surge protection. He likely will need to first pin
the inspector down on what rules he's allegely broken, however.

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
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

Yeah, I am waiting on the exact code violation to come down. FWIW the overall consent from various fire marshalls is 'yes, it's fine' but some had misgivings about it. understandable, and strictly according to atleast one rule book it isn't allowed.

At which point two questions arise:

1) is that 'rulebook' controlling by law, and if so, where does that
delegation of authority happen in statute, and

2) what will your *fire insurer* think about it even if it is legal?

Cheers,
-- jr 'IANAL:IJPOOTI' a