Harold,
opto couplers are a good idea up to 10KV isolation. Isolated supply at 10KV
it's usually expensive but up to 1KV it's easy to find:
http://www.newark.com/recom-power/roe-0505s/dc-dc-converter-1w-5v-0-2a-sip/=
dp/63X9545
Buried cable is less susceptible to lighting. I will not be extremely
worried but depends what do you have at the end.

Vasile


On Sat, May 16, 2015 at 8:39 PM, Harold Hallikainen <harold@hallikainen.org=
>
wrote:

> I'm working on an application where contact closures will be sensed by a
> PIC inside a building, but the contacts are outside (perhaps tens of
> meters away). What sort of protection for the inputs is suggested? What
> sort of protection is required by regulatory standards for equipment
> connecting to outside wiring? The outside wiring would likely be buried,
> but lightning could still induce currents into buried cables. Opto
> couplers are one way to get the isolation, but then you have to power the
> LEDs with an isolated supply. Ideas?
>
> Thanks!
>
> Harold
>
>
>
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