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so tom  did lightning take out his modem?



"w_tom" <w_tom1@hotmail.com> wrote in message
news:3F3C237C.7A74E7E9@hotmail.com...
> This discussion is cross posted to numerous newsgroups - not
> just a UK newsgroup.  Concept of breakdown voltages still
> apply on both sides of the pond.  For example isolation
> transformer in modem's DAA circuit may provide 2000 volts of
> galvanic isolation.  However destructive common mode surges
> are current sources.  That current will increase voltage, as
> necessary, to turn that transformer or optocoupler into a
> conductor. Either they provide isolation without damage, or
> they do not and become damaged as surge passes through.
> Through seeking what?  Earth ground.
>
>   Protector components do not sacrifice themselves to protect
> electronics.  Either destructive current flows through them or
> no current flows - no damage.  But again, destructive common
> mode surges cannot be stopped, blocked, filtered, or
> absorbed.  As in a flood, the dam will not stop a flood.  A
> dike will divert the flood, but only if the flood is shunted
> downstream.  Galvanic isolation works like a dike.  Only
> effective IF the surge has some other, non-destructive path
> downstream - to earth ground.  That is what the 'whole house'
> protector does; shunt the surge downstream to earth.
>
>   Appliances already have galvanic isolation.  But again, that
> internal protection will only be effective IF the surge is
> earthed before entering a building.  Appliances already have
> 'dikes' that will be overwhelmed if the surge is not earthed
> before entering the building.  Just as dikes work for the
> town.  If flood is not provided a downstream path, then 'dike'
> is acting like a dam - and is overwhelmed.
>
>   There are no sacrificial components in an effective
> protection system.  Even a thyristor based crowbar circuit is
> properly sized to shunt without damage.   A common mode
> transient either does nothing to the optocoupler OR creates a
> plasma path through that optocoupler.  A direct lightning
> strike is earthed without damage to transistors or the
> protector.  Protection is not difficult and performed so often
> that protector damage is not an option.  No sacrificial
> components are found or used in an effective protection
> system.
>
> www.ees-group.co.uk/downloads/Secondary%20Effects.pdf
> An interesting discussion, but where does this apply to
> anything posted here?  What numbers apply to this discussion?
>
>   We know how to protect everything from direct lightning
> strikes without damage even to the surge protectors.  Moreso,
> the protection is so inexpensive.  However plug-in protectors
> ARE expensive and not  effective protection - which is why
> they don't even claim to provide such protection.
>
>   Described in the previous post is how effective protection
> from direct lightning strikes is implemented - complete with
> products and where they can be purchased.  Even the
> www.ees-group.co.uk article does not dispute what was posted.
> Bottom line is this: a surge protector is only as effective as
> its earth ground.
>
>
> Nigel Kendrick wrote:
> > "w_tom" <w_tom1@usa.net> wrote in message
> > news:dfee1359.0308120333.5a970e26@posting.google.com...
> > > As soon as a read about 'fusible' components that protect other
> > components, then I know the poster does not have electrical training.
> >
> > Actually, I'm an electronics engineer by training, including 4 years on
an
> > electronics engineering apprenticeship and a total of 6 years as an
> > electronics design engineer for visual systems for flight simulators.
> >
> > > > either have a fusible transformer that 'sacrifices' itself in the
event
> > of a surge in order to protect the PC,
> >
> > Instead of 'transformer', I should have written 'isolation circuit'. The
> > transformer isolation circuit in a modem includes components to damp
mild
> > surges - MOVs, gas arrestors, zener / avalanche diodes etc. These will
fail
> > in the presence of *massive* surges but will often damp down potentially
> > damaging (to the PC) surges to safer levels.
> >
> > >   There is no sacrifical component to save electronics - except where
> > urban myth replaces electrical knowledge.
> >
> > Obviously not seen a crowbar circuit then--but that's off topic :-)
> >
> > > In the UK, this is different
> >
> > Freeserve is a UK ISP and so it would be safe to assume that all
discussion
> > points in this newsgroup should be based on UK conditions
> >
> > >   Furthermore the concept of breakdown voltage is totally unknow to
> > > the poster.
> > > Even optocouplers have breakdown voltages typically starting at 2000
> > volts.
> >
> > Er, no it isn't but I wasn't specifically referring to breakdown or
> > flashover between the input and output of the opto isolator - a surge on
the
> > input circuit will damage the opto isolator even if the applied emf is
> > insufficient to flash over to the output side so, in effect, the opto
> > isolator has sacrificed itself in order to protect other equipment.
> >
> > > Surge damage is easier in UK where even the phone line has no 'whole
> > house' protector.
> >
> > Exactly
> >
> > >
> > >   That claim of EMP induced surges is only another urban myth that
> > > falls flat on its face when the myth purveryor cannot provide numbers
> > > to support that claim.  Appliances have such good internal protection
> > > that only the direct strike causes damage.
> >
> > You want numbers - OK, read the following article which has data related
to
> > electromagnetic pulse damage caused by lightning.
> >
> > www.ees-group.co.uk/downloads/Secondary%20Effects.pdf
> >
> > NK