🚀 go-pugleaf

 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