[mythtv-users] OT:Protection of htpc from power surge through incoming cable

Stephen P. Villano stephen.p.villano at gmail.com
Wed Nov 6 14:38:55 UTC 2013


On 11/6/13 7:56 AM, Eric Sharkey wrote:
> On Wed, Nov 6, 2013 at 7:00 AM, Simon Hobson <linux at thehobsons.co.uk> wrote:
>> Rajil Saraswat wrote:
>>> Is there any way to stop power surge through the incoming cable in the future?
>> It's very tricky getting this sort of thing right - and many people do it wrong !
>>
>> Example of getting it wrong. User has a problem with surges in the phone line
>> damaging the modem. So they get a surge protector extension lead with phone
>> sockets - and routes the phone line through it as well as plugging in the modem.
>> The next surge is diverted into the earth wire of the socket strip, so the earth in
>> the socket strip now has a spike on it. This feeds up the mains lead fo the modem
> Wouldn't that be an example of a surge protector manufacturer doing it wrong?
>
> Eric
> _______________________________________________
>
Not really, if you're layering your defenses.
Back when I repaired televisions, a customer had a dead television and a
dead dishwasher from a direct lightning strike on the service pole to
his house.
He happened to be an industrial electrician and had installed an
industrial load center and industrial surge protector onto the mains
coming into his home, plus a good, solid earth ground in the form of a
copper grounding rod driven 8 feet into the ground.
The total carnage was a timer for the dishwasher and new motor, a fuse
for the television, the load center bus bar insulation had carbon trails
resulting in its replacement and the surge protector was literally blown
flat against his basement wall.
Had he also put in branch protectors at the load connection points, he'd
have probably not lost his dishwasher motor and timer.
I really doubt anyone cares about the fuse and MOV I replaced (just to
be sure, if the MOV conducted enough to blow the fuse, replace it lest
it break down in a month).

We don't get strikes that often in my area, the trees tend to protect
the power poles here. We do get near misses, ground current
differentials within 100 feet in some areas in my locality (not so much
at my home, the water table is too high due to clay a few feet down
holding the water).
So, the copper ground on both sides of the house works well. One for the
cable that is no longer in use, the other for electrical power and the
no longer used copper telephone lines (we're on fiber now).
Two because the cable entry was on the opposite side of the house from
the electrical and telephone entry points. I also had the demarc for the
phone moved outside and was only moved inside again (it was originally
hidden in the basement ceiling, behind drywall) when we switched to fiber.

Now, if only I could get the extra cash to get a whole house generator
that runs off of natural gas. Those trees protect the lines from
strikes, but those same trees drop branches onto the high voltage lines
far too frequently, in spite of the local electric company clearing
their right of way.


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