Re: Is Zone Alarm necessary with a DSL firewall?



On Nov 12, 12:37 pm, DanS <t.h.i.s.n.t.h....@xxxxxxxxxxxxxxxxxxxxx>
wrote:
"w_tom" <w_t...@xxxxxxx> wrote innews:1163352053.423395.18750@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:

You are talking about surges. That is lightning. We install surge
protection for a typically destructive surge - lightning. Other surges
made irrelevant by same protection

NO, you install a lightning protector to protect against lightning.
I do agree with w_ that surge suppressors can protect against
lightning, depending on suppressor rating, surge rating and where the
hit occurrs. They may not protect from an unlikely direct hit to a
house, but can protect from surges coming in on power and signal
wiring. (You may be talking about direct strikes and lightning rods. Or
tower antennas.)


Well, I have provided you with numbers...the APC one, claiming around 900
joules, and I looked up the Monster item you keep speaking about. That
indicates 1600 joules. But apparently you do not read entire posts. Or
you just ignore anything you don't like.

So....let's do the math.

1 Watt = 1 Joule / one second

1000 joules = 1000 watts/one second.

A 10 ms surge = 100,000 watts.

A 5 ms surge = 200,000 watts.

A 1 ms surge = 1,000,000 watts.

Therefore, your 12,000 volts at 100 amps for 1ms figures to be 1.2
millions watts. So, the Monster (suprisingly) would, IN THEORY, absorb
this, depending on how long it lasts. And let's face it, this is ALL
theory.


Reading ahead I know you don't necessarily see these as realistic
numbers, but some comments. The energy dissipation in a MOV is based on
the clamping voltage across it. A surge suppressor may have a rated
clamp voltage of 400V, and the voltage across the MOV will go up to
maybe 500 or 600V with tens of thousands of amps in a service panel
protector. Wiring impedance significantly lowers the current for
plug-in suppressors unless very near the service panel. The clamp
voltage (400-600V here) determines the energy hit the MOV receives. The
most severe surges are typically lightning derived. A stroke is on the
order of 100 microseconds (but there may be multiple strokes).

If you had a 10,000A surge lasting 100 microseconds to a MOV that
clamped at 600V the device would dissipate 600J.

--
bud--

.

Relevant Pages

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