🚀 go-pugleaf

"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