Re: Surge / Ground / Lightning

In alt.tv.tech.hdtv Franc Zabkar <fzabkar@[EMAIL PROTECTED]
> wrote:
| On 3 May 2008 09:46:09 GMT, phil-news-nospam@[EMAIL PROTECTED]
 put finger to
| keyboard and composed:
| 
|>In alt.tv.tech.hdtv Franc Zabkar <fzabkar@[EMAIL PROTECTED]
> wrote:
|>| On Thu, 1 May 2008 13:30:31 -0700 (PDT), w_tom <w_tom1@[EMAIL PROTECTED]
> put
|>| finger to keyboard and composed:
|>| 
|>|>On May 1, 2:18?pm, ransley <Mark_Rans...@[EMAIL PROTECTED]
> wrote:
|>|>> Whaaat, you say my Triplights that offer a life time warranty to
|>|>> damages from from surges and lightning offer non such ?claim or
|>|>> warranty, thats pure barf. Triplight surge protectors are only one
|>|>> step a homeowner needs to hopefully protect you. Ive been hit
several
|>|>> times, anything you do helps a bit.
|>|>
|>|>  Actually some things installed will decrease protection - ie the TV
|>|>destroyed because the plug-in protector earthed an 8000 volt surge
|>|>through it.
|>| 
|>| Can you elaborate on this by showing us the path taken by the strike
|>| through the TV?
|>
|>A surge will take _every_ path.  Where that ends up with a voltage
difference
|>somewhere, anywhere, that exceeds the device breakdown voltage, then you
will
|>have current flow across there.  And if that breakdown means damage, as
it
|>would for things like a CMOS circuit component, the device would be
damaged.
| 
| True but irrelevant to my question. I wanted specific examples in
| sup****t of the claim that "some things installed will decrease
| protection".

Installing something that ends up creating a situation where you will have
a
big voltage difference where you otherwise would not is such an example.


| A strike on the mains would be clamped to the earth pin by MOVs. It
| may still be that the antenna provides a second path to earth which
| would mean that the TV could be damaged that way. However, the absence
| of an earth pin would result in an even higher differential voltage
| between mains and antenna which would mean an even greater likelihood
| of damage. OTOH, if the strike arrived via the antenna, then the
| presence or absence of the earth pin should make very little
| difference AFAICS.

The MOVs will act like conductors when they are clamping.  The surge will
take both paths ... the path through the MOVs, and the path going past the
MOVs.  In general, about 50% will go each way.  That can vary at higher
frequencies.

The antenna "second path to earth" could provide that difference in
voltage
that can lead to substantial and damaging current.  However, if you bring
the antenna feedline in at the point electric power comes in, and ground
everything in common, then whatever voltage rise you get in low
frequencies
will be fairly equal between power connection and antenna connection.  The
strike coming in on the antenna is not really any different, except in the
high frequencies.  The antenna feedline does not degrade the high
frequencies
as much as the power lines.

The high frequencies can still be an issue.  They are less common so if
you
are just trying to reduce your risk then this is a good start.  Most
energy
is in lower frequencies (though this varies by means of entry).  But there
are ways to deal with the high frequency energy as well, if you want to go
that far.  It just depends on how much you want to spend to get how much
protection.

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